... but make it a config option so that broken environments can disable
it when required.
We really should always have a clean build, and will disable specific
over-eager warnings as required, if we can't fix them. But while I
fairly religiously enforce that in my own tree, it doesn't get enforced
by various build robots that don't necessarily report warnings.
So this just makes '-Werror' a default compiler flag, but allows people
to disable it for their configuration if they have some particular
issues.
Occasionally, new compiler versions end up enabling new warnings, and it
can take a while before we have them fixed (or the warnings disabled if
that is what it takes), so the config option allows for that situation.
Hopefully this will mean that I get fewer pull requests that have new
warnings that were not noticed by various automation we have in place.
Knock wood.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
- Add -s option (strict mode) to merge_config.sh to make it fail when
any symbol is redefined.
- Show a warning if a different compiler is used for building external
modules.
- Infer --target from ARCH for CC=clang to let you cross-compile the
kernel without CROSS_COMPILE.
- Make the integrated assembler default (LLVM_IAS=1) for CC=clang.
- Add <linux/stdarg.h> to the kernel source instead of borrowing
<stdarg.h> from the compiler.
- Add Nick Desaulniers as a Kbuild reviewer.
- Drop stale cc-option tests.
- Fix the combination of CONFIG_TRIM_UNUSED_KSYMS and CONFIG_LTO_CLANG
to handle symbols in inline assembly.
- Show a warning if 'FORCE' is missing for if_changed rules.
- Various cleanups
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Merge tag 'kbuild-v5.15' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild
Pull Kbuild updates from Masahiro Yamada:
- Add -s option (strict mode) to merge_config.sh to make it fail when
any symbol is redefined.
- Show a warning if a different compiler is used for building external
modules.
- Infer --target from ARCH for CC=clang to let you cross-compile the
kernel without CROSS_COMPILE.
- Make the integrated assembler default (LLVM_IAS=1) for CC=clang.
- Add <linux/stdarg.h> to the kernel source instead of borrowing
<stdarg.h> from the compiler.
- Add Nick Desaulniers as a Kbuild reviewer.
- Drop stale cc-option tests.
- Fix the combination of CONFIG_TRIM_UNUSED_KSYMS and CONFIG_LTO_CLANG
to handle symbols in inline assembly.
- Show a warning if 'FORCE' is missing for if_changed rules.
- Various cleanups
* tag 'kbuild-v5.15' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild: (39 commits)
kbuild: redo fake deps at include/ksym/*.h
kbuild: clean up objtool_args slightly
modpost: get the *.mod file path more simply
checkkconfigsymbols.py: Fix the '--ignore' option
kbuild: merge vmlinux_link() between ARCH=um and other architectures
kbuild: do not remove 'linux' link in scripts/link-vmlinux.sh
kbuild: merge vmlinux_link() between the ordinary link and Clang LTO
kbuild: remove stale *.symversions
kbuild: remove unused quiet_cmd_update_lto_symversions
gen_compile_commands: extract compiler command from a series of commands
x86: remove cc-option-yn test for -mtune=
arc: replace cc-option-yn uses with cc-option
s390: replace cc-option-yn uses with cc-option
ia64: move core-y in arch/ia64/Makefile to arch/ia64/Kbuild
sparc: move the install rule to arch/sparc/Makefile
security: remove unneeded subdir-$(CONFIG_...)
kbuild: sh: remove unused install script
kbuild: Fix 'no symbols' warning when CONFIG_TRIM_UNUSD_KSYMS=y
kbuild: Switch to 'f' variants of integrated assembler flag
kbuild: Shuffle blank line to improve comment meaning
...
-Wunused-but-set-variable and -Wunused-const-variable are both disabled
for the same reason but there is a blank line between them and no blank
line between -Wno-unused-const-variable and the block.
Shuffle the new line so that it is clear that the comment applied to
both flags and the next block is separate from them.
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Whenever a warning is disabled, it is helpful for future travelers to
understand why the warning is disabled and why it is acceptable to do
so. Add a comment for -Wno-gnu so that people understand why it is
disabled.
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Turning on -Wformat does not reveal any instances of this warning across
several different builds so remove this line to keep the number of
disabled warnings as slim as possible.
This has been disabled since commit 61163efae0 ("kbuild: LLVMLinux:
Add Kbuild support for building kernel with Clang"), which does not
explain exactly why it was turned off but since it was so long ago in
terms of both the kernel and LLVM so it is possible that some bug got
fixed along the way.
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
cc-option, cc-option-yn, and cc-disable-warning all invoke the compiler
during build time, and can slow down the build when these checks become
stale for our supported compilers, whose minimally supported versions
increases over time. See Documentation/process/changes.rst for the
current supported minimal versions (GCC 4.9+, clang 10.0.1+). Compiler
version support for these flags may be verified on godbolt.org.
The following flags are GCC only and supported since at least GCC 4.9.
Remove cc-option and cc-disable-warning tests.
* -fno-tree-loop-im
* -Wno-maybe-uninitialized
* -fno-reorder-blocks
* -fno-ipa-cp-clone
* -fno-partial-inlining
* -femit-struct-debug-baseonly
* -fno-inline-functions-called-once
* -fconserve-stack
The following flags are supported by all supported versions of GCC and
Clang. Remove their cc-option, cc-option-yn, and cc-disable-warning tests.
* -fno-delete-null-pointer-checks
* -fno-var-tracking
* -Wno-array-bounds
The following configs are made dependent on GCC, since they use GCC
specific flags.
* READABLE_ASM
* DEBUG_SECTION_MISMATCH
-mfentry was not supported by s390-linux-gnu-gcc until gcc-9+, add a
comment.
--param=allow-store-data-races=0 was renamed to -fno-allow-store-data-races
in the GCC 10 release; add a comment.
-Wmaybe-uninitialized (GCC specific) was being added for CONFIG_GCOV,
then again unconditionally; add it only once.
Also, base RETPOLINE_CFLAGS and RETPOLINE_VDSO_CFLAGS on CONFIC_CC_IS_*
then remove cc-option tests for Clang.
Link: https://github.com/ClangBuiltLinux/linux/issues/1436
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
- Fix a kernel crash when a signal is delivered to bad userspace stack
- Fix fall-through warnings in math-emu code
- Increase size of gcc stack frame check
- Switch coding from 'pci_' to 'dma_' API
- Make struct parisc_driver::remove() return void
- Some parisc related Makefile changes
- Minor cleanups, e.g. change to octal permissions, fix macro collisions,
fix PMD_ORDER collision, replace spaces with tabs
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Merge tag 'for-5.15/parisc' of git://git.kernel.org/pub/scm/linux/kernel/git/deller/parisc-linux
Pull parisc architecture updates from Helge Deller:
- Fix a kernel crash when a signal is delivered to bad userspace stack
- Fix fall-through warnings in math-emu code
- Increase size of gcc stack frame check
- Switch coding from 'pci_' to 'dma_' API
- Make struct parisc_driver::remove() return void
- Some parisc related Makefile changes
- Minor cleanups, e.g. change to octal permissions, fix macro
collisions, fix PMD_ORDER collision, replace spaces with tabs
* tag 'for-5.15/parisc' of git://git.kernel.org/pub/scm/linux/kernel/git/deller/parisc-linux:
parisc: math-emu: Fix fall-through warnings
parisc: fix crash with signals and alloca
parisc: Fix compile failure when building 64-bit kernel natively
parisc: ccio-dma.c: Added tab instead of spaces
parisc/parport_gsc: switch from 'pci_' to 'dma_' API
parisc: move core-y in arch/parisc/Makefile to arch/parisc/Kbuild
parisc: switch from 'pci_' to 'dma_' API
parisc: Make struct parisc_driver::remove() return void
parisc: remove unused arch/parisc/boot/install.sh and its phony target
parisc: Rename PMD_ORDER to PMD_TABLE_ORDER
parisc: math-emu: Avoid "fmt" macro collision
parisc: Increase size of gcc stack frame check
parisc: Replace symbolic permissions with octal permissions
- Expand lib/test_stackinit to include more initialization styles
- Improve Kconfig for CLang's auto-var-init feature
- Introduce support for GCC's zero-call-used-regs feature
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Merge tag 'hardening-v5.15-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux
Pull hardening updates from Kees Cook:
- Expand lib/test_stackinit to include more initialization styles
- Improve Kconfig for CLang's auto-var-init feature
- Introduce support for GCC's zero-call-used-regs feature
* tag 'hardening-v5.15-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
lib/test_stackinit: Add assigned initializers
lib/test_stackinit: Allow building stand-alone
lib/test_stackinit: Fix static initializer test
hardening: Clarify Kconfig text for auto-var-init
hardening: Introduce CONFIG_ZERO_CALL_USED_REGS
Commit 23243c1ace ("arch: use cross_compiling to check whether it is
a cross build or not") broke 64-bit parisc builds on 32-bit parisc
systems.
Helge mentioned:
- 64-bit parisc userspace is not supported yet [1]
- hppa gcc does not support "-m64" flag [2]
That means, parisc developers working on a 32-bit parisc machine need
to use hppa64-linux-gnu-gcc (cross compiler) for building the 64-bit
parisc kernel.
After the offending commit, gcc is used in such a case because
both $(SRCARCH) and $(SUBARCH) are 'parisc', hence cross_compiling is
unset.
A correct way is to introduce ARCH=parisc64 because building the 64-bit
parisc kernel on a 32-bit parisc system is not exactly a native build,
but rather a semi-cross build.
[1]: https://lore.kernel.org/linux-parisc/5dfd81eb-c8ca-b7f5-e80e-8632767c022d@gmx.de/#t
[2]: https://lore.kernel.org/linux-parisc/89515325-fc21-31da-d238-6f7a9abbf9a0@gmx.de/
Fixes: 23243c1ace ("arch: use cross_compiling to check whether it is a cross build or not")
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reported-by: Meelis Roos <mroos@linux.ee>
Tested-by: Meelis Roos <mroos@linux.ee>
Cc: <stable@vger.kernel.org> # v5.13+
Signed-off-by: Helge Deller <deller@gmx.de>
LLVM_IAS is the user interface to set the -(no-)integrated-as flag,
and it should be used only for that purpose.
LLVM_IAS is checked in some places to determine the assembler type,
but it is not precise.
For example,
$ make CC=gcc LLVM_IAS=1
... will use the GNU assembler (i.e. binutils) since LLVM_IAS=1 is
effective only when $(CC) is clang.
Of course, 'CC=gcc LLVM_IAS=1' is an odd combination, but the build
system can be more robust against such insane input.
Commit ba64beb174 ("kbuild: check the minimum assembler version in
Kconfig") introduced CONFIG_AS_IS_GNU/LLVM, which is more precise
because Kconfig checks the version string from the assembler in use.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
With some of the changes we'd like to make to CROSS_COMPILE, the initial
block of clang flag handling which controls things like the target triple,
whether or not to use the integrated assembler and how to find GAS,
and erroring on unknown warnings is becoming unwieldy. Move it into its
own file under scripts/.
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
It is always safe to use the same compiler for the kernel and external
modules, but in reality, some distributions such as Fedora release a
different version of GCC from the one used for building the kernel.
There was a long discussion about mixing different compilers [1].
I do not repeat it here, but at least, showing a heads up in that
case is better than nothing.
Linus suggested [2]:
And a warning might be more palatable even if different compiler
version work fine together. Just a heads up on "it looks like you
might be mixing compiler versions" is a valid note, and isn't
necessarily wrong. Even when they work well together, maybe you want
to have people at least _aware_ of it.
This commit shows a warning unless the compiler is exactly the same.
warning: the compiler differs from the one used to build the kernel
The kernel was built by: gcc (GCC) 11.1.1 20210531 (Red Hat 11.1.1-3)
You are using: gcc (GCC) 11.2.1 20210728 (Red Hat 11.2.1-1)
Check the difference, and if it is OK with you, please proceed at your
risk.
To avoid the locale issue as in commit bcbcf50f52 ("kbuild: fix
ld-version.sh to not be affected by locale"), pass LC_ALL=C to
"$(CC) --version".
[1] https://lore.kernel.org/linux-hardening/efe6b039a544da8215d5e54aa7c4b6d1986fc2b0.1611607264.git.jpoimboe@redhat.com/
[2] https://lore.kernel.org/lkml/CAHk-=wgjwhDy-y4mQh34L+2aF=n6BjzHdqAW2=8wri5x7O04pA@mail.gmail.com/
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
As explained in commit 3204a7fb98 ("kbuild: prefix $(srctree)/ to some
included Makefiles"), I want to stop using --include-dir some day.
I already fixed up the top Makefile, but some arch Makefiles (mips, um,
x86) still include check-in Makefiles without $(srctree)/.
Fix them up so 'need-sub-make := 1' can go away for this case.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
- Correct the Extended Regular Expressions in tools
- Adjust scripts/checkversion.pl for the current Kbuild
- Unset sub_make_done for 'make install' to make DKMS working again
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Merge tag 'kbuild-fixes-v5.14-2' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild
Pull Kbuild fixes from Masahiro Yamada:
- Correct the Extended Regular Expressions in tools
- Adjust scripts/checkversion.pl for the current Kbuild
- Unset sub_make_done for 'make install' to make DKMS work again
* tag 'kbuild-fixes-v5.14-2' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild:
kbuild: cancel sub_make_done for the install target to fix DKMS
scripts: checkversion: modernize linux/version.h search strings
mips: Fix non-POSIX regexp
x86/tools/relocs: Fix non-POSIX regexp
- Fix NULL pointer dereference caused by an error path
- Give histogram calculation fields a size, otherwise it breaks synthetic
creation based on them.
- Reject strings being used for number calculations.
- Fix recordmcount.pl warning on llvm building RISC-V allmodconfig
- Fix the draw_functrace.py script to handle the new trace output
- Fix warning of smp_processor_id() in preemptible code
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Merge tag 'trace-v5.14-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace
Pull tracing fixes from Steven Rostedt:
"Various tracing fixes:
- Fix NULL pointer dereference caused by an error path
- Give histogram calculation fields a size, otherwise it breaks
synthetic creation based on them.
- Reject strings being used for number calculations.
- Fix recordmcount.pl warning on llvm building RISC-V allmodconfig
- Fix the draw_functrace.py script to handle the new trace output
- Fix warning of smp_processor_id() in preemptible code"
* tag 'trace-v5.14-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
tracing: Quiet smp_processor_id() use in preemptable warning in hwlat
scripts/tracing: fix the bug that can't parse raw_trace_func
scripts/recordmcount.pl: Remove check_objcopy() and $can_use_local
tracing: Reject string operand in the histogram expression
tracing / histogram: Give calculation hist_fields a size
tracing: Fix NULL pointer dereference in start_creating
Since commit bcf637f54f ("kbuild: parse C= and M= before changing the
working directory"), external module builds invoked by DKMS fail because
M= option is not parsed.
I wanted to add 'unset sub_make_done' in install.sh but similar scripts,
arch/*/boot/install.sh, are duplicated, so I set sub_make_done empty in
the top Makefile.
Fixes: bcf637f54f ("kbuild: parse C= and M= before changing the working directory")
Reported-by: John S Gruber <johnsgruber@gmail.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: John S Gruber <johnsgruber@gmail.com>
When building ARCH=riscv allmodconfig with llvm-objcopy, the objcopy
version warning from this script appears:
WARNING: could not find objcopy version or version is less than 2.17.
Local function references are disabled.
The check_objcopy() function in scripts/recordmcount.pl is set up to
parse GNU objcopy's version string, not llvm-objcopy's, which triggers
the warning.
Commit 799c434154 ("kbuild: thin archives make default for all archs")
made binutils 2.20 mandatory and commit ba64beb174 ("kbuild: check the
minimum assembler version in Kconfig") enforces this at configuration
time so just remove check_objcopy() and $can_use_local instead, assuming
--globalize-symbol is always available.
llvm-objcopy has supported --globalize-symbol since LLVM 7.0.0 in 2018
and the minimum version for building the kernel with LLVM is 10.0.1 so
there is no issue introduced:
Link: ee5be798da
Link: https://lkml.kernel.org/r/20210802210307.3202472-1-nathan@kernel.org
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
When CONFIG_ZERO_CALL_USED_REGS is enabled, build the kernel with
"-fzero-call-used-regs=used-gpr" (in GCC 11). This option will zero any
caller-used register contents just before returning from a function,
ensuring that temporary values are not leaked beyond the function
boundary. This means that register contents are less likely to be
available for side channel attacks and information exposures.
Additionally this helps reduce the number of useful ROP gadgets in the
kernel image by about 20%:
$ ROPgadget.py --nosys --nojop --binary vmlinux.stock | tail -n1
Unique gadgets found: 337245
$ ROPgadget.py --nosys --nojop --binary vmlinux.zero-call-regs | tail -n1
Unique gadgets found: 267175
and more notably removes simple "write-what-where" gadgets:
$ ROPgadget.py --ropchain --binary vmlinux.stock | sed -n '/Step 1/,/Step 2/p'
- Step 1 -- Write-what-where gadgets
[+] Gadget found: 0xffffffff8102d76c mov qword ptr [rsi], rdx ; ret
[+] Gadget found: 0xffffffff81000cf5 pop rsi ; ret
[+] Gadget found: 0xffffffff8104d7c8 pop rdx ; ret
[-] Can't find the 'xor rdx, rdx' gadget. Try with another 'mov [reg], reg'
[+] Gadget found: 0xffffffff814c2b4c mov qword ptr [rsi], rdi ; ret
[+] Gadget found: 0xffffffff81000cf5 pop rsi ; ret
[+] Gadget found: 0xffffffff81001e51 pop rdi ; ret
[-] Can't find the 'xor rdi, rdi' gadget. Try with another 'mov [reg], reg'
[+] Gadget found: 0xffffffff81540d61 mov qword ptr [rsi], rdi ; pop rbx ; pop rbp ; ret
[+] Gadget found: 0xffffffff81000cf5 pop rsi ; ret
[+] Gadget found: 0xffffffff81001e51 pop rdi ; ret
[-] Can't find the 'xor rdi, rdi' gadget. Try with another 'mov [reg], reg'
[+] Gadget found: 0xffffffff8105341e mov qword ptr [rsi], rax ; ret
[+] Gadget found: 0xffffffff81000cf5 pop rsi ; ret
[+] Gadget found: 0xffffffff81029a11 pop rax ; ret
[+] Gadget found: 0xffffffff811f1c3b xor rax, rax ; ret
- Step 2 -- Init syscall number gadgets
$ ROPgadget.py --ropchain --binary vmlinux.zero* | sed -n '/Step 1/,/Step 2/p'
- Step 1 -- Write-what-where gadgets
[-] Can't find the 'mov qword ptr [r64], r64' gadget
For an x86_64 parallel build tests, this has a less than 1% performance
impact, and grows the image size less than 1%:
$ size vmlinux.stock vmlinux.zero-call-regs
text data bss dec hex filename
22437676 8559152 14127340 45124168 2b08a48 vmlinux.stock
22453184 8563248 14110956 45127388 2b096dc vmlinux.zero-call-regs
Impact for other architectures may vary. For example, arm64 sees a 5.5%
image size growth, mainly due to needing to always clear x16 and x17:
https://lore.kernel.org/lkml/20210510134503.GA88495@C02TD0UTHF1T.local/
Signed-off-by: Kees Cook <keescook@chromium.org>
- Restore the original behavior of scripts/setlocalversion when
LOCALVERSION is set to empty.
- Show Kconfig prompts even for 'make -s'
- Fix the combination of COFNIG_LTO_CLANG=y and CONFIG_MODVERSIONS=y
for older GNU Make versions
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Merge tag 'kbuild-fixes-v5.14' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild
Pull Kbuild fixes from Masahiro Yamada:
- Restore the original behavior of scripts/setlocalversion when
LOCALVERSION is set to empty.
- Show Kconfig prompts even for 'make -s'
- Fix the combination of COFNIG_LTO_CLANG=y and CONFIG_MODVERSIONS=y
for older GNU Make versions
* tag 'kbuild-fixes-v5.14' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild:
Documentation: Fix intiramfs script name
Kbuild: lto: fix module versionings mismatch in GNU make 3.X
kbuild: do not suppress Kconfig prompts for silent build
scripts/setlocalversion: fix a bug when LOCALVERSION is empty
When a new CONFIG option is available, Kbuild shows a prompt to get
the user input.
$ make
[ snip ]
Core Scheduling for SMT (SCHED_CORE) [N/y/?] (NEW)
This is the only interactive place in the build process.
Commit 174a1dcc96 ("kbuild: sink stdout from cmd for silent build")
suppressed Kconfig prompts as well because syncconfig is invoked by
the 'cmd' macro. You cannot notice the fact that Kconfig is waiting
for the user input.
Use 'kecho' to show the equivalent short log without suppressing stdout
from sub-make.
Fixes: 174a1dcc96 ("kbuild: sink stdout from cmd for silent build")
Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
This reverts commit b7eb335e26.
It turns out that the problem with the clang -Wimplicit-fallthrough
warning is not about the kernel source code, but about clang itself, and
that the warning is unusable until clang fixes its broken ways.
In particular, when you enable this warning for clang, you not only get
warnings about implicit fallthroughs. You also get this:
warning: fallthrough annotation in unreachable code [-Wimplicit-fallthrough]
which is completely broken becasue it
(a) doesn't even tell you where the problem is (seriously: no line
numbers, no filename, no nothing).
(b) is fundamentally broken anyway, because there are perfectly valid
reasons to have a fallthrough statement even if it turns out that
it can perhaps not be reached.
In the kernel, an example of that second case is code in the scheduler:
switch (state) {
case cpuset:
if (IS_ENABLED(CONFIG_CPUSETS)) {
cpuset_cpus_allowed_fallback(p);
state = possible;
break;
}
fallthrough;
case possible:
where if CONFIG_CPUSETS is enabled you actually never hit the
fallthrough case at all. But that in no way makes the fallthrough
wrong.
So the warning is completely broken, and enabling it for clang is a very
bad idea.
In the meantime, we can keep the gcc option enabled, and make the gcc
build use
-Wimplicit-fallthrough=5
which means that we will at least continue to require a proper
fallthrough statement, and that gcc won't silently accept the magic
comment versions. Because gcc does this all correctly, and while the odd
"=5" part is kind of obscure, it's documented in [1]:
"-Wimplicit-fallthrough=5 doesn’t recognize any comments as
fallthrough comments, only attributes disable the warning"
so if clang ever fixes its bad behavior we can try enabling it there again.
Link: https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html [1]
Cc: Kees Cook <keescook@chromium.org>
Cc: Gustavo A. R. Silva <gustavoars@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
With the recent fixes for fallthrough warnings, it is now possible to
enable -Wimplicit-fallthrough for Clang.
It's important to mention that since we have adopted the use of the
pseudo-keyword macro fallthrough; we also want to avoid having more
/* fall through */ comments being introduced. Notice that contrary
to GCC, Clang doesn't recognize any comments as implicit fall-through
markings when the -Wimplicit-fallthrough option is enabled. So, in
order to avoid having more comments being introduced, we have to use
the option -Wimplicit-fallthrough=5 for GCC, which similar to Clang,
will cause a warning in case a code comment is intended to be used
as a fall-through marking.
Co-developed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
- Increase the -falign-functions alignment for the debug option.
- Remove ugly libelf checks from the top Makefile.
- Make the silent build (-s) more silent.
- Re-compile the kernel if KBUILD_BUILD_TIMESTAMP is specified.
- Various script cleanups
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Merge tag 'kbuild-v5.14' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild
Pull Kbuild updates from Masahiro Yamada:
- Increase the -falign-functions alignment for the debug option.
- Remove ugly libelf checks from the top Makefile.
- Make the silent build (-s) more silent.
- Re-compile the kernel if KBUILD_BUILD_TIMESTAMP is specified.
- Various script cleanups
* tag 'kbuild-v5.14' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild: (27 commits)
scripts: add generic syscallnr.sh
scripts: check duplicated syscall number in syscall table
sparc: syscalls: use pattern rules to generate syscall headers
parisc: syscalls: use pattern rules to generate syscall headers
nds32: add arch/nds32/boot/.gitignore
kbuild: mkcompile_h: consider timestamp if KBUILD_BUILD_TIMESTAMP is set
kbuild: modpost: Explicitly warn about unprototyped symbols
kbuild: remove trailing slashes from $(KBUILD_EXTMOD)
kconfig.h: explain IS_MODULE(), IS_ENABLED()
kconfig: constify long_opts
scripts/setlocalversion: simplify the short version part
scripts/setlocalversion: factor out 12-chars hash construction
scripts/setlocalversion: add more comments to -dirty flag detection
scripts/setlocalversion: remove workaround for old make-kpkg
scripts/setlocalversion: remove mercurial, svn and git-svn supports
kbuild: clean up ${quiet} checks in shell scripts
kbuild: sink stdout from cmd for silent build
init: use $(call cmd,) for generating include/generated/compile.h
kbuild: merge scripts/mkmakefile to top Makefile
sh: move core-y in arch/sh/Makefile to arch/sh/Kbuild
...
- Optimise SVE switching for CPUs with 128-bit implementations.
- Fix output format from SVE selftest.
- Add support for versions v1.2 and 1.3 of the SMC calling convention.
- Allow Pointer Authentication to be configured independently for
kernel and userspace.
- PMU driver cleanups for managing IRQ affinity and exposing event
attributes via sysfs.
- KASAN optimisations for both hardware tagging (MTE) and out-of-line
software tagging implementations.
- Relax frame record alignment requirements to facilitate 8-byte
alignment with KASAN and Clang.
- Cleanup of page-table definitions and removal of unused memory types.
- Reduction of ARCH_DMA_MINALIGN back to 64 bytes.
- Refactoring of our instruction decoding routines and addition of some
missing encodings.
- Move entry code moved into C and hardened against harmful compiler
instrumentation.
- Update booting requirements for the FEAT_HCX feature, added to v8.7
of the architecture.
- Fix resume from idle when pNMI is being used.
- Additional CPU sanity checks for MTE and preparatory changes for
systems where not all of the CPUs support 32-bit EL0.
- Update our kernel string routines to the latest Cortex Strings
implementation.
- Big cleanup of our cache maintenance routines, which were confusingly
named and inconsistent in their implementations.
- Tweak linker flags so that GDB can understand vmlinux when using RELR
relocations.
- Boot path cleanups to enable early initialisation of per-cpu
operations needed by KCSAN.
- Non-critical fixes and miscellaneous cleanup.
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Merge tag 'arm64-upstream' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux
Pull arm64 updates from Will Deacon:
"There's a reasonable amount here and the juicy details are all below.
It's worth noting that the MTE/KASAN changes strayed outside of our
usual directories due to core mm changes and some associated changes
to some other architectures; Andrew asked for us to carry these [1]
rather that take them via the -mm tree.
Summary:
- Optimise SVE switching for CPUs with 128-bit implementations.
- Fix output format from SVE selftest.
- Add support for versions v1.2 and 1.3 of the SMC calling
convention.
- Allow Pointer Authentication to be configured independently for
kernel and userspace.
- PMU driver cleanups for managing IRQ affinity and exposing event
attributes via sysfs.
- KASAN optimisations for both hardware tagging (MTE) and out-of-line
software tagging implementations.
- Relax frame record alignment requirements to facilitate 8-byte
alignment with KASAN and Clang.
- Cleanup of page-table definitions and removal of unused memory
types.
- Reduction of ARCH_DMA_MINALIGN back to 64 bytes.
- Refactoring of our instruction decoding routines and addition of
some missing encodings.
- Move entry code moved into C and hardened against harmful compiler
instrumentation.
- Update booting requirements for the FEAT_HCX feature, added to v8.7
of the architecture.
- Fix resume from idle when pNMI is being used.
- Additional CPU sanity checks for MTE and preparatory changes for
systems where not all of the CPUs support 32-bit EL0.
- Update our kernel string routines to the latest Cortex Strings
implementation.
- Big cleanup of our cache maintenance routines, which were
confusingly named and inconsistent in their implementations.
- Tweak linker flags so that GDB can understand vmlinux when using
RELR relocations.
- Boot path cleanups to enable early initialisation of per-cpu
operations needed by KCSAN.
- Non-critical fixes and miscellaneous cleanup"
* tag 'arm64-upstream' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux: (150 commits)
arm64: tlb: fix the TTL value of tlb_get_level
arm64: Restrict undef hook for cpufeature registers
arm64/mm: Rename ARM64_SWAPPER_USES_SECTION_MAPS
arm64: insn: avoid circular include dependency
arm64: smp: Bump debugging information print down to KERN_DEBUG
drivers/perf: fix the missed ida_simple_remove() in ddr_perf_probe()
perf/arm-cmn: Fix invalid pointer when access dtc object sharing the same IRQ number
arm64: suspend: Use cpuidle context helpers in cpu_suspend()
PSCI: Use cpuidle context helpers in psci_cpu_suspend_enter()
arm64: Convert cpu_do_idle() to using cpuidle context helpers
arm64: Add cpuidle context save/restore helpers
arm64: head: fix code comments in set_cpu_boot_mode_flag
arm64: mm: drop unused __pa(__idmap_text_start)
arm64: mm: fix the count comments in compute_indices
arm64/mm: Fix ttbr0 values stored in struct thread_info for software-pan
arm64: mm: Pass original fault address to handle_mm_fault()
arm64/mm: Drop SECTION_[SHIFT|SIZE|MASK]
arm64/mm: Use CONT_PMD_SHIFT for ARM64_MEMSTART_SHIFT
arm64/mm: Drop SWAPPER_INIT_MAP_SIZE
arm64: Conditionally configure PTR_AUTH key of the kernel.
...
M= (or KBUILD_EXTMOD) generally expects a directory path without any
trailing slashes, like M=a/b/c.
If you add a trailing slash, like M=a/b/c/, you will get ugly build
logs (two slashes in a series), but it still works fine as long as it
is consistent between 'make modules' and 'make modules_install'.
The following commands correctly build and install the modules.
$ make M=a/b/c/ modules
$ sudo make M=a/b/c/ modules_install
Since commit ccae4cfa7b ("kbuild: refactor scripts/Makefile.modinst"),
a problem happens if you add a trailing slash only for modules_install.
$ make M=a/b/c modules
$ sudo make M=a/b/c/ modules_install
No module is installed in this case, Johannes Berg reported. [1]
Trim any trailing slashes from $(KBUILD_EXTMOD).
I used the 'dirname' command to remove all the trailing slashes in
case someone adds more slashes like M=a/b/c/////. The Make's built-in
function, $(dir ...) cannot take care of such a case.
[1]: https://lore.kernel.org/lkml/10cc8522b27a051e6a9c3e158a4c4b6414fd04a0.camel@sipsolutions.net/
Fixes: ccae4cfa7b ("kbuild: refactor scripts/Makefile.modinst")
Reported-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
- The "-warn-stack-size" option under LTO has moved in Clang 13 (Tor Vic)
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Merge tag 'clang-features-v5.13-rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux
Pull clang LTO fix from Kees Cook:
"It seems Clang has been scrubbing through the missing LTO IR flags for
Clang 13, and the last of these 'only with LTO' flags is fixed now.
I've asked that they please consider making these changes in a less
'break all the Clang kernel builds' kind of way in the future. :P
Summary:
- The '-warn-stack-size' option under LTO has moved in Clang 13 (Tor
Vic)"
* tag 'clang-features-v5.13-rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
Makefile: lto: Pass -warn-stack-size only on LLD < 13.0.0
Since LLVM commit fc018eb, the '-warn-stack-size' flag has been dropped
[1], leading to the following error message when building with Clang-13
and LLD-13:
ld.lld: error: -plugin-opt=-: ld.lld: Unknown command line argument
'-warn-stack-size=2048'. Try: 'ld.lld --help'
ld.lld: Did you mean '--asan-stack=2048'?
In the same way as with commit 2398ce8015 ("x86, lto: Pass
-stack-alignment only on LLD < 13.0.0") , make '-warn-stack-size'
conditional on LLD < 13.0.0.
[1] https://reviews.llvm.org/D103928
Fixes: 24845dcb17 ("Makefile: LTO: have linker check -Wframe-larger-than")
Cc: stable@vger.kernel.org
Link: https://github.com/ClangBuiltLinux/linux/issues/1377
Signed-off-by: Tor Vic <torvic9@mailbox.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/7631bab7-a8ab-f884-ab54-f4198976125c@mailbox.org
GDB produces the following warning when debugging kernels built with
CONFIG_RELR:
BFD: /android0/linux-next/vmlinux: unknown type [0x13] section `.relr.dyn'
when loading a kernel built with CONFIG_RELR into GDB. It can also
prevent debugging symbols using such relocations.
Peter sugguests:
[That flag] means that lld will use dynamic tags and section type
numbers in the OS-specific range rather than the generic range. The
kernel itself doesn't care about these numbers; it determines the
location of the RELR section using symbols defined by a linker script.
Link: https://github.com/ClangBuiltLinux/linux/issues/1057
Suggested-by: Peter Collingbourne <pcc@google.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/r/20210522012626.2811297-1-ndesaulniers@google.com
Signed-off-by: Will Deacon <will@kernel.org>
scripts/mkmakefile is simple enough to be merged in the Makefile.
Use $(call cmd,...) to show the log instead of doing it in the
shell script.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
arch/$(SRCARCH)/Kbuild is useful for Makefile cleanups because you can
use the obj-y syntax.
Add an empty file if it is missing in arch/$(SRCARCH)/.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
-Wframe-larger-than= requires stack frame information, which the
frontend cannot provide. This diagnostic is emitted late during
compilation once stack frame size is available.
When building with LTO, the frontend simply lowers C to LLVM IR and does
not have stack frame information, so it cannot emit this diagnostic.
When the linker drives LTO, it restarts optimizations and lowers LLVM IR
to object code. At that point, it has stack frame information but
doesn't know to check for a specific max stack frame size.
I consider this a bug in LLVM that we need to fix. There are some
details we're working out related to LTO such as which value to use when
there are multiple different values specified per TU, or how to
propagate these to compiler synthesized routines properly, if at all.
Until it's fixed, ensure we don't miss these. At that point we can wrap
this in a compiler version guard or revert this based on the minimum
support version of Clang.
The error message is not generated during link:
LTO vmlinux.o
ld.lld: warning: stack size limit exceeded (8224) in foobarbaz
Cc: Sami Tolvanen <samitolvanen@google.com>
Reported-by: Candle Sun <candlesea@gmail.com>
Suggested-by: Fangrui Song <maskray@google.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210312010942.1546679-1-ndesaulniers@google.com
I do not see a good reason why only the libelf development package must
be so carefully checked.
Kbuild generally does not check host tools or libraries.
For example, x86_64 defconfig fails to build with no libssl development
package installed.
scripts/extract-cert.c:21:10: fatal error: openssl/bio.h: No such file or directory
21 | #include <openssl/bio.h>
| ^~~~~~~~~~~~~~~
To solve the build error, you need to install libssl-dev or openssl-devel
package, depending on your distribution.
'apt-file search', 'dnf provides', etc. is your frined to find a proper
package to install.
This commit removes all the libelf checks from the top Makefile.
If libelf is missing, objtool will fail to build in a similar pattern:
.../linux/tools/objtool/include/objtool/elf.h:10:10: fatal error: gelf.h: No such file or directory
10 | #include <gelf.h>
You need to install libelf-dev, libelf-devel, or elfutils-libelf-devel
to proceed.
Another remarkable change is, CONFIG_STACK_VALIDATION (without
CONFIG_UNWINDER_ORC) previously continued to build with a warning,
but now it will treat missing libelf as an error.
This is just a one-time installation, so it should not hurt to break
a build and make a user install the package.
BTW, the traditional way to handle such checks is autotool, but according
to [1], I do not expect the kernel build would have similar scripting
like './configure' does.
[1]: https://lore.kernel.org/lkml/CA+55aFzr2HTZVOuzpHYDwmtRJLsVzE-yqg2DHpHi_9ePsYp5ug@mail.gmail.com/
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
The tools/ directory only exists in the kernel source tree, not in
external modules.
Do not expose the meaningless targets to external modules.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Commit 09c60546f0 ("./Makefile: add debug option to enable
function aligned on 32 bytes") was introduced to help debugging
strange kernel performance changes caused by code alignment
change.
Recently we found 2 similar cases [1][2] caused by code-alignment
changes, which can only be identified by forcing 64 bytes aligned
for all functions.
Originally, 32 bytes was used mainly for not wasting too much
text space, but this option is only for debug anyway where text
space is not a big concern. So extend the alignment to 64 bytes
to cover more similar cases.
[1].https://lore.kernel.org/lkml/20210427090013.GG32408@xsang-OptiPlex-9020/
[2].https://lore.kernel.org/lkml/20210420030837.GB31773@xsang-OptiPlex-9020/
Signed-off-by: Feng Tang <feng.tang@intel.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
- Convert sh and sparc to use generic shell scripts to generate the
syscall headers
- refactor .gitignore files
- Update kernel/config_data.gz only when the content of the .config is
really changed, which avoids the unneeded re-link of vmlinux
- move "remove stale files" workarounds to scripts/remove-stale-files
- suppress unused-but-set-variable warnings by default for Clang as well
- fix locale setting LANG=C to LC_ALL=C
- improve 'make distclean'
- always keep intermediate objects from scripts/link-vmlinux.sh
- move IF_ENABLED out of <linux/kconfig.h> to make it self-contained
- misc cleanups
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Merge tag 'kbuild-v5.13-2' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild
Pull more Kbuild updates from Masahiro Yamada:
- Convert sh and sparc to use generic shell scripts to generate the
syscall headers
- refactor .gitignore files
- Update kernel/config_data.gz only when the content of the .config
is really changed, which avoids the unneeded re-link of vmlinux
- move "remove stale files" workarounds to scripts/remove-stale-files
- suppress unused-but-set-variable warnings by default for Clang
as well
- fix locale setting LANG=C to LC_ALL=C
- improve 'make distclean'
- always keep intermediate objects from scripts/link-vmlinux.sh
- move IF_ENABLED out of <linux/kconfig.h> to make it self-contained
- misc cleanups
* tag 'kbuild-v5.13-2' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild: (25 commits)
linux/kconfig.h: replace IF_ENABLED() with PTR_IF() in <linux/kernel.h>
kbuild: Don't remove link-vmlinux temporary files on exit/signal
kbuild: remove the unneeded comments for external module builds
kbuild: make distclean remove tag files in sub-directories
kbuild: make distclean work against $(objtree) instead of $(srctree)
kbuild: refactor modname-multi by using suffix-search
kbuild: refactor fdtoverlay rule
kbuild: parameterize the .o part of suffix-search
arch: use cross_compiling to check whether it is a cross build or not
kbuild: remove ARCH=sh64 support from top Makefile
.gitignore: prefix local generated files with a slash
kbuild: replace LANG=C with LC_ALL=C
Makefile: Move -Wno-unused-but-set-variable out of GCC only block
kbuild: add a script to remove stale generated files
kbuild: update config_data.gz only when the content of .config is changed
.gitignore: ignore only top-level modules.builtin
.gitignore: move tags and TAGS close to other tag files
kernel/.gitgnore: remove stale timeconst.h and hz.bc
usr/include: refactor .gitignore
genksyms: fix stale comment
...
The supported targets for external modules are listed in the help target
a few lines below. Let's not have duplicated information in two places.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
'make tags' and friends create tag files in the top directory, but
people may manually create tag files in sub-directories.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
This reverts the old commit [1], which seems questionable to me.
It claimed 'make distclean' could not remove editor backup files,
but I believe KBUILD_OUTPUT or O= was set.
When O= is given, Kbuild should always work against $(objtree).
If O= is not given, $(objtree) and $(srctree) are the same, therefore
$(srctree) is cleaned up.
[1]: https://git.kernel.org/pub/scm/linux/kernel/git/history/history.git/commit/?id=dd47df980c02eb33833b2690b033c34fba2fa80d
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Commit 37744feebc ("sh: remove sh5 support") removed the SUPERH64
support entirely.
Remove the left-over code from the top Makefile.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
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Merge tag 'integrity-v5.13' of git://git.kernel.org/pub/scm/linux/kernel/git/zohar/linux-integrity
Pull IMA updates from Mimi Zohar:
"In addition to loading the kernel module signing key onto the builtin
keyring, load it onto the IMA keyring as well.
Also six trivial changes and bug fixes"
* tag 'integrity-v5.13' of git://git.kernel.org/pub/scm/linux/kernel/git/zohar/linux-integrity:
ima: ensure IMA_APPRAISE_MODSIG has necessary dependencies
ima: Fix fall-through warnings for Clang
integrity: Add declarations to init_once void arguments.
ima: Fix function name error in comment.
ima: enable loading of build time generated key on .ima keyring
ima: enable signing of modules with build time generated key
keys: cleanup build time module signing keys
ima: Fix the error code for restoring the PCR value
ima: without an IMA policy loaded, return quickly
Currently, -Wunused-but-set-variable is only supported by GCC so it is
disabled unconditionally in a GCC only block (it is enabled with W=1).
clang currently has its implementation for this warning in review so
preemptively move this statement out of the GCC only block and wrap it
with cc-disable-warning so that both compilers function the same.
Cc: stable@vger.kernel.org
Link: https://reviews.llvm.org/D100581
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
We maintain .gitignore and Makefiles so build artifacts are properly
ignored by Git, and cleaned up by 'make clean'. However, the code is
always changing; generated files are often moved to another directory,
or removed when they become unnecessary. Such garbage files tend to be
left over in the source tree because people usually git-pull without
cleaning the tree.
This is not only the noise for 'git status', but also a build issue
in some cases.
One solution is to remove a stale file like commit 223c24a7db ("kbuild:
Automatically remove stale <linux/version.h> file") did. Such workaround
should be removed after a while, but we forget about that if we scatter
the workaround code in random places.
So, this commit adds a new script to collect cleanings of stale files.
As a start point, move the code in arch/arm/boot/compressed/Makefile
into this script.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
- Change 'option defconfig' to the environment variable
KCONFIG_DEFCONFIG_LIST
- Refactor tinyconfig without using allnoconfig_y
- Remove 'option allnoconfig_y' syntax
- Change 'option modules' to 'modules'
- Do not use /boot/config-* etc. as base config for cross-compilation
- Fix a search bug in nconf
- Various code cleanups
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Merge tag 'kconfig-v5.13' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild
Pull Kconfig updates from Masahiro Yamada:
- Change 'option defconfig' to the environment variable
KCONFIG_DEFCONFIG_LIST
- Refactor tinyconfig without using allnoconfig_y
- Remove 'option allnoconfig_y' syntax
- Change 'option modules' to 'modules'
- Do not use /boot/config-* etc. as base config for cross-compilation
- Fix a search bug in nconf
- Various code cleanups
* tag 'kconfig-v5.13' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild: (34 commits)
kconfig: refactor .gitignore
kconfig: highlight xconfig 'comment' lines with '***'
kconfig: highlight gconfig 'comment' lines with '***'
kconfig: gconf: remove unused code
kconfig: remove unused PACKAGE definition
kconfig: nconf: stop endless search loops
kconfig: split menu.c out of parser.y
kconfig: nconf: refactor in print_in_middle()
kconfig: nconf: remove meaningless wattrset() call from show_menu()
kconfig: nconf: change set_config_filename() to void function
kconfig: nconf: refactor attributes setup code
kconfig: nconf: remove unneeded default for menu prompt
kconfig: nconf: get rid of (void) casts from wattrset() calls
kconfig: nconf: fix NORMAL attributes
kconfig: mconf,nconf: remove unneeded '\0' termination after snprintf()
kconfig: use /boot/config-* etc. as DEFCONFIG_LIST only for native build
kconfig: change sym_change_count to a boolean flag
kconfig: nconf: fix core dump when searching in empty menu
kconfig: lxdialog: A spello fix and a punctuation added
kconfig: streamline_config.pl: Couple of typo fixes
...
- Evaluate $(call cc-option,...) etc. only for build targets
- Add CONFIG_VMLINUX_MAP to generate .map file when linking vmlinux
- Remove unnecessary --gcc-toolchains Clang flag because the --prefix
flag finds the toolchains
- Do not pass Clang's --prefix flag when using the integrated as
- Check the assembler version in Kconfig time
- Add new CONFIG options, AS_VERSION, AS_IS_GNU, AS_IS_LLVM to clean up
some dependencies in Kconfig
- Fix invalid Module.symvers creation when building only modules without
vmlinux
- Fix false-positive modpost warnings when CONFIG_TRIM_UNUSED_KSYMS is
set, but there is no module to build
- Refactor module installation Makefile
- Support zstd for module compression
- Convert alpha and ia64 to use generic shell scripts to generate the
syscall headers
- Add a new elfnote to indicate if the kernel was built with LTO, which
will be used by pahole
- Flatten the directory structure under include/config/ so CONFIG options
and filenames match
- Change the deb source package name from linux-$(KERNELRELEASE) to
linux-upstream
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Merge tag 'kbuild-v5.13' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild
Pull Kbuild updates from Masahiro Yamada:
- Evaluate $(call cc-option,...) etc. only for build targets
- Add CONFIG_VMLINUX_MAP to generate .map file when linking vmlinux
- Remove unnecessary --gcc-toolchains Clang flag because the --prefix
flag finds the toolchains
- Do not pass Clang's --prefix flag when using the integrated as
- Check the assembler version in Kconfig time
- Add new CONFIG options, AS_VERSION, AS_IS_GNU, AS_IS_LLVM to clean up
some dependencies in Kconfig
- Fix invalid Module.symvers creation when building only modules
without vmlinux
- Fix false-positive modpost warnings when CONFIG_TRIM_UNUSED_KSYMS is
set, but there is no module to build
- Refactor module installation Makefile
- Support zstd for module compression
- Convert alpha and ia64 to use generic shell scripts to generate the
syscall headers
- Add a new elfnote to indicate if the kernel was built with LTO, which
will be used by pahole
- Flatten the directory structure under include/config/ so CONFIG
options and filenames match
- Change the deb source package name from linux-$(KERNELRELEASE) to
linux-upstream
* tag 'kbuild-v5.13' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild: (42 commits)
kbuild: Add $(KBUILD_HOSTLDFLAGS) to 'has_libelf' test
kbuild: deb-pkg: change the source package name to linux-upstream
tools: do not include scripts/Kbuild.include
kbuild: redo fake deps at include/config/*.h
kbuild: remove TMPO from try-run
MAINTAINERS: add pattern for dummy-tools
kbuild: add an elfnote for whether vmlinux is built with lto
ia64: syscalls: switch to generic syscallhdr.sh
ia64: syscalls: switch to generic syscalltbl.sh
alpha: syscalls: switch to generic syscallhdr.sh
alpha: syscalls: switch to generic syscalltbl.sh
sysctl: use min() helper for namecmp()
kbuild: add support for zstd compressed modules
kbuild: remove CONFIG_MODULE_COMPRESS
kbuild: merge scripts/Makefile.modsign to scripts/Makefile.modinst
kbuild: move module strip/compression code into scripts/Makefile.modinst
kbuild: refactor scripts/Makefile.modinst
kbuild: rename extmod-prefix to extmod_prefix
kbuild: check module name conflict for external modules as well
kbuild: show the target directory for depmod log
...
- Clean up list_sort prototypes (Sami Tolvanen)
- Introduce CONFIG_CFI_CLANG for arm64 (Sami Tolvanen)
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Merge tag 'cfi-v5.13-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux
Pull CFI on arm64 support from Kees Cook:
"This builds on last cycle's LTO work, and allows the arm64 kernels to
be built with Clang's Control Flow Integrity feature. This feature has
happily lived in Android kernels for almost 3 years[1], so I'm excited
to have it ready for upstream.
The wide diffstat is mainly due to the treewide fixing of mismatched
list_sort prototypes. Other things in core kernel are to address
various CFI corner cases. The largest code portion is the CFI runtime
implementation itself (which will be shared by all architectures
implementing support for CFI). The arm64 pieces are Acked by arm64
maintainers rather than coming through the arm64 tree since carrying
this tree over there was going to be awkward.
CFI support for x86 is still under development, but is pretty close.
There are a handful of corner cases on x86 that need some improvements
to Clang and objtool, but otherwise works well.
Summary:
- Clean up list_sort prototypes (Sami Tolvanen)
- Introduce CONFIG_CFI_CLANG for arm64 (Sami Tolvanen)"
* tag 'cfi-v5.13-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
arm64: allow CONFIG_CFI_CLANG to be selected
KVM: arm64: Disable CFI for nVHE
arm64: ftrace: use function_nocfi for ftrace_call
arm64: add __nocfi to __apply_alternatives
arm64: add __nocfi to functions that jump to a physical address
arm64: use function_nocfi with __pa_symbol
arm64: implement function_nocfi
psci: use function_nocfi for cpu_resume
lkdtm: use function_nocfi
treewide: Change list_sort to use const pointers
bpf: disable CFI in dispatcher functions
kallsyms: strip ThinLTO hashes from static functions
kthread: use WARN_ON_FUNCTION_MISMATCH
workqueue: use WARN_ON_FUNCTION_MISMATCH
module: ensure __cfi_check alignment
mm: add generic function_nocfi macro
cfi: add __cficanonical
add support for Clang CFI
Provide support for randomized stack offsets per syscall to make
stack-based attacks harder which rely on the deterministic stack layout.
The feature is based on the original idea of PaX's RANDSTACK feature, but
uses a significantly different implementation.
The offset does not affect the pt_regs location on the task stack as this
was agreed on to be of dubious value. The offset is applied before the
actual syscall is invoked.
The offset is stored per cpu and the randomization happens at the end of
the syscall which is less predictable than on syscall entry.
The mechanism to apply the offset is via alloca(), i.e. abusing the
dispised VLAs. This comes with the drawback that stack-clash-protection
has to be disabled for the affected compilation units and there is also
a negative interaction with stack-protector.
Those downsides are traded with the advantage that this approach does not
require any intrusive changes to the low level assembly entry code, does
not affect the unwinder and the correct stack alignment is handled
automatically by the compiler.
The feature is guarded with a static branch which avoids the overhead when
disabled.
Currently this is supported for X86 and ARM64.
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Merge tag 'x86-entry-2021-04-26' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull entry code update from Thomas Gleixner:
"Provide support for randomized stack offsets per syscall to make
stack-based attacks harder which rely on the deterministic stack
layout.
The feature is based on the original idea of PaX's RANDSTACK feature,
but uses a significantly different implementation.
The offset does not affect the pt_regs location on the task stack as
this was agreed on to be of dubious value. The offset is applied
before the actual syscall is invoked.
The offset is stored per cpu and the randomization happens at the end
of the syscall which is less predictable than on syscall entry.
The mechanism to apply the offset is via alloca(), i.e. abusing the
dispised VLAs. This comes with the drawback that
stack-clash-protection has to be disabled for the affected compilation
units and there is also a negative interaction with stack-protector.
Those downsides are traded with the advantage that this approach does
not require any intrusive changes to the low level assembly entry
code, does not affect the unwinder and the correct stack alignment is
handled automatically by the compiler.
The feature is guarded with a static branch which avoids the overhead
when disabled.
Currently this is supported for X86 and ARM64"
* tag 'x86-entry-2021-04-26' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
arm64: entry: Enable random_kstack_offset support
lkdtm: Add REPORT_STACK for checking stack offsets
x86/entry: Enable random_kstack_offset support
stack: Optionally randomize kernel stack offset each syscall
init_on_alloc: Optimize static branches
jump_label: Provide CONFIG-driven build state defaults
Normally, invocations of $(HOSTCC) include $(KBUILD_HOSTLDFLAGS), which
in turn includes $(HOSTLDFLAGS), which allows users to pass in their own
flags when linking. However, the 'has_libelf' test does not, meaning
that if a user requests a specific linker via HOSTLDFLAGS=-fuse-ld=...,
it is not respected and the build might error.
For example, if a user building with clang wants to use all of the LLVM
tools without any GNU tools, they might remove all of the GNU tools from
their system or PATH then build with
$ make HOSTLDFLAGS=-fuse-ld=lld LLVM=1 LLVM_IAS=1
which says use all of the LLVM tools, the integrated assembler, and
ld.lld for linking host executables. Without this change, the build will
error because $(HOSTCC) uses its default linker, rather than the one
requested via -fuse-ld=..., which is GNU ld in clang's case in a default
configuration.
error: Cannot generate ORC metadata for CONFIG_UNWINDER_ORC=y, please
install libelf-dev, libelf-devel or elfutils-libelf-devel
make[1]: *** [Makefile:1260: prepare-objtool] Error 1
Add $(KBUILD_HOSTLDFLAGS) to the 'has_libelf' test so that the linker
choice is respected.
Link: https://github.com/ClangBuiltLinux/linux/issues/479
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
scripts/Makefile.modsign is a subset of scripts/Makefile.modinst,
and duplicates the code. Let's merge them.
By the way, you do not need to run 'make modules_sign' explicitly
because modules are signed as a part of 'make modules_install' when
CONFIG_MODULE_SIG_ALL=y. If CONFIG_MODULE_SIG_ALL=n, mod_sign_cmd is
set to 'true', so 'make modules_sign' is not functional.
In my understanding, the reason of still keeping this is to handle
corner cases like commit 64178cb62c ("builddeb: fix stripped module
signatures if CONFIG_DEBUG_INFO and CONFIG_MODULE_SIG_ALL are set").
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Both mod_strip_cmd and mod_compress_cmd are only used in
scripts/Makefile.modinst, hence there is no good reason to define them
in the top Makefile. Move the relevant code to scripts/Makefile.modinst.
Also, show separate log messages for each of install, strip, sign, and
compress.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
scripts/Makefile.modinst is ugly and weird in multiple ways; it
specifies real files $(modules) as phony, makes directory manipulation
needlessly too complicated.
Clean up the Makefile code, and show the full path of installed modules
in the log.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
This seems to be useful in sub-make as well. As a preparation of
exporting it, rename extmod-prefix to extmod_prefix because exported
variables cannot contain hyphens.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
If there are multiple modules with the same name in the same external
module tree, there is ambiguity about which one will be loaded, and
very likely something odd is happening.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
If you attempt to build or install modules ('make modules(_install)'
with CONFIG_MODULES disabled, you will get a clear error message, but
nothing for external module builds.
Factor out the modules and modules_install rules into the common part,
so you will get the same error message when you try to build external
modules with CONFIG_MODULES=n.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
The external module build shows the following warning if Module.symvers
is missing in the kernel tree.
WARNING: Symbol version dump "Module.symvers" is missing.
Modules may not have dependencies or modversions.
I think this is an important heads-up because the resulting modules may
not work as expected. This happens when you did not build the entire
kernel tree, for example, you might have prepared the minimal setups
for external modules by 'make defconfig && make modules_preapre'.
A problem is that 'make modules' creates Module.symvers even without
vmlinux. In this case, that warning is suppressed since Module.symvers
already exists in spite of its incomplete content.
The incomplete (i.e. invalid) Module.symvers should not be created.
This commit changes the second pass of modpost to dump symbols into
modules-only.symvers. The final Module.symvers is created by
concatenating vmlinux.symvers and modules-only.symvers if both exist.
Module.symvers is supposed to collect symbols from both vmlinux and
modules. It might be a bit confusing, and I am not quite sure if it
is an official interface, but presumably it is difficult to rename it
because some tools (e.g. kmod) parse it.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Documentation/process/changes.rst defines the minimum assembler version
(binutils version), but we have never checked it in the build time.
Kbuild never invokes 'as' directly because all assembly files in the
kernel tree are *.S, hence must be preprocessed. I do not expect
raw assembly source files (*.s) would be added to the kernel tree.
Therefore, we always use $(CC) as the assembler driver, and commit
aa824e0c96 ("kbuild: remove AS variable") removed 'AS'. However,
we are still interested in the version of the assembler acting behind.
As usual, the --version option prints the version string.
$ as --version | head -n 1
GNU assembler (GNU Binutils for Ubuntu) 2.35.1
But, we do not have $(AS). So, we can add the -Wa prefix so that
$(CC) passes --version down to the backing assembler.
$ gcc -Wa,--version | head -n 1
gcc: fatal error: no input files
compilation terminated.
OK, we need to input something to satisfy gcc.
$ gcc -Wa,--version -c -x assembler /dev/null -o /dev/null | head -n 1
GNU assembler (GNU Binutils for Ubuntu) 2.35.1
The combination of Clang and GNU assembler works in the same way:
$ clang -no-integrated-as -Wa,--version -c -x assembler /dev/null -o /dev/null | head -n 1
GNU assembler (GNU Binutils for Ubuntu) 2.35.1
Clang with the integrated assembler fails like this:
$ clang -integrated-as -Wa,--version -c -x assembler /dev/null -o /dev/null | head -n 1
clang: error: unsupported argument '--version' to option 'Wa,'
For the last case, checking the error message is fragile. If the
proposal for -Wa,--version support [1] is accepted, this may not be
even an error in the future.
One easy way is to check if -integrated-as is present in the passed
arguments. We did not pass -integrated-as to CLANG_FLAGS before, but
we can make it explicit.
Nathan pointed out -integrated-as is the default for all of the
architectures/targets that the kernel cares about, but it goes
along with "explicit is better than implicit" policy. [2]
With all this in my mind, I implemented scripts/as-version.sh to
check the assembler version in Kconfig time.
$ scripts/as-version.sh gcc
GNU 23501
$ scripts/as-version.sh clang -no-integrated-as
GNU 23501
$ scripts/as-version.sh clang -integrated-as
LLVM 0
[1]: https://github.com/ClangBuiltLinux/linux/issues/1320
[2]: https://lore.kernel.org/linux-kbuild/20210307044253.v3h47ucq6ng25iay@archlinux-ax161/
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
For simple text replacement, it is better to use a built-in function
instead of sed if possible. You can save one process forking.
I do not mean to replace all sed invocations because GNU Make itself
does not support regular expression (unless you use guile).
I just replaced simple ones.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
When building with LLVM_IAS=1, there is no point to specifying
'--prefix=' because that flag is only used to find GNU cross tools,
which will not be used indirectly when using the integrated assembler.
All of the tools are invoked directly from PATH or a full path specified
via the command line, which does not depend on the value of '--prefix='.
Sharing commands to reproduce issues becomes a little bit easier without
a '--prefix=' value because that '--prefix=' value is specific to a
user's machine due to it being an absolute path.
Some further notes from Fangrui Song:
clang can spawn GNU as (if -f?no-integrated-as is specified) and GNU
objcopy (-f?no-integrated-as and -gsplit-dwarf and -g[123]).
objcopy is only used for GNU as assembled object files.
With integrated assembler, the object file streamer creates .o and
.dwo simultaneously.
With GNU as, two objcopy commands are needed to extract .debug*.dwo to
.dwo files && another command to remove .debug*.dwo sections.
A small consequence of this change (to keep things simple) is that
'--prefix=' will always be specified now, even with a native build, when
it was not before. This should not be an issue due to the way that the
Makefile searches for the prefix (based on elfedit's location). This
ends up improving the experience for host builds because PATH is better
respected and matches GCC's behavior more closely. See the below thread
for more details:
https://lore.kernel.org/r/20210205213651.GA16907@Ryzen-5-4500U.localdomain/
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
This flag was originally added to allow clang to find the GNU cross
tools in commit 785f11aa59 ("kbuild: Add better clang cross build
support"). This flag was not enough to find the tools at times so
'--prefix' was added to the list in commit ef8c4ed9db ("kbuild: allow
to use GCC toolchain not in Clang search path") and improved upon in
commit ca9b31f6bb ("Makefile: Fix GCC_TOOLCHAIN_DIR prefix for Clang
cross compilation"). Now that '--prefix' specifies a full path and
prefix, '--gcc-toolchain' serves no purpose because the kernel builds
with '-nostdinc' and '-nostdlib'.
This has been verified with self compiled LLVM 10.0.1 and LLVM 13.0.0 as
well as a distribution version of LLVM 11.1.0 without binutils in the
LLVM toolchain locations.
Link: https://reviews.llvm.org/D97902
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Fangrui Song <maskray@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
The patch adding CONFIG_VMLINUX_MAP revealed a small defect in the
build system: link-vmlinux.sh takes decisions based on CONFIG_*
options, but changing one of those does not always lead to vmlinux
being linked again.
For most of the CONFIG_* knobs referenced previously, this has
probably been hidden by those knobs also affecting some object file,
hence indirectly also vmlinux.
But CONFIG_VMLINUX_MAP is only handled inside link-vmlinux.sh, and
changing CONFIG_VMLINUX_MAP=n to CONFIG_VMLINUX_MAP=y does not cause
the build system to re-link (and hence have vmlinux.map
emitted). Since that map file is mostly a debugging aid, this is
merely a nuisance which is easily worked around by just deleting
vmlinux and building again.
But one could imagine other (possibly future) CONFIG options that
actually do affect the vmlinux binary but which are not captured
through some object file dependency.
To fix this, make link-vmlinux.sh emit a .vmlinux.d file in the same
format as the dependency files generated by gcc, and apply the fixdep
logic to that. I've tested that this correctly works with both in-tree
and out-of-tree builds.
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Since commit 7ecaf069da ("kbuild: move headers_check rule to
usr/include/Makefile"), 'make headers_check' is no-op.
This stub target is remaining here in case some scripts still invoke it.
In order to prompt people to remove stale code, show a noisy warning
message if used. The stub will be really removed after the Linux 5.15
release.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Since commit f2f02ebd8f ("kbuild: improve cc-option to clean up all
temporary files"), running 'make kernelversion' in a read-only source
tree emits a bunch of warnings:
mkdir: cannot create directory '.tmp_12345': Permission denied
No-build targets such as kernelversion, clean, help, etc. do not
need to evaluate $(call cc-option,) or friends. Skip Makefile.compiler
so $(call cc-option,) becomes no-op.
This not only fixes the warnings, but also runs non-build targets much
faster.
Basically, all installation targets should also be non-build targets.
Unfortunately, vdso_install requires the compiler because it builds
vdso before installation. This is a problem that must be fixed by a
separate patch.
Reported-by: Israel Tsadok <itsadok@gmail.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
scripts/Kbuild.include is included everywhere, but macros such as
cc-option are needed by build targets only.
For example, when 'make clean' traverses the tree, it does not need
to evaluate $(call cc-option,).
Split cc-option, ld-option, etc. to scripts/Makefile.compiler, which
is only included from the top Makefile and scripts/Makefile.build.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
When the .config file is missing, 'make config', 'make menuconfig', etc.
uses a file listed in DEFCONFIG_LIST, if found, as base configuration.
Ususally, /boot/config-$(uname -r) exists, and is used as default.
However, when you are cross-compiling the kernel, it does not make
sense to use /boot/config-* on the build host. It should default to
arch/$(SRCARCH)/configs/$(KBUILD_DEFCONFIG).
UML previously did not use DEFCONFIG_LIST at all, but it should be
able to use arch/um/configs/$(KBUILD_DEFCONFIG) as a base config file.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
This is a partial revert of commit 2a86f66121 ("kbuild: use
KBUILD_DEFCONFIG as the fallback for DEFCONFIG_LIST").
Now that the reference to $(DEFCONFIG_LIST) was removed from
init/Kconfig, the default KBUILD_DEFCONFIG can go back home.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
The "mrproper" target is still looking for build time generated keys in
the kernel root directory instead of certs directory. Fix the path and
remove the names of the files which are no longer generated.
Fixes: cfc411e7ff ("Move certificate handling to its own directory")
Signed-off-by: Nayna Jain <nayna@linux.ibm.com>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
This change adds support for Clang’s forward-edge Control Flow
Integrity (CFI) checking. With CONFIG_CFI_CLANG, the compiler
injects a runtime check before each indirect function call to ensure
the target is a valid function with the correct static type. This
restricts possible call targets and makes it more difficult for
an attacker to exploit bugs that allow the modification of stored
function pointers. For more details, see:
https://clang.llvm.org/docs/ControlFlowIntegrity.html
Clang requires CONFIG_LTO_CLANG to be enabled with CFI to gain
visibility to possible call targets. Kernel modules are supported
with Clang’s cross-DSO CFI mode, which allows checking between
independently compiled components.
With CFI enabled, the compiler injects a __cfi_check() function into
the kernel and each module for validating local call targets. For
cross-module calls that cannot be validated locally, the compiler
calls the global __cfi_slowpath_diag() function, which determines
the target module and calls the correct __cfi_check() function. This
patch includes a slowpath implementation that uses __module_address()
to resolve call targets, and with CONFIG_CFI_CLANG_SHADOW enabled, a
shadow map that speeds up module look-ups by ~3x.
Clang implements indirect call checking using jump tables and
offers two methods of generating them. With canonical jump tables,
the compiler renames each address-taken function to <function>.cfi
and points the original symbol to a jump table entry, which passes
__cfi_check() validation. This isn’t compatible with stand-alone
assembly code, which the compiler doesn’t instrument, and would
result in indirect calls to assembly code to fail. Therefore, we
default to using non-canonical jump tables instead, where the compiler
generates a local jump table entry <function>.cfi_jt for each
address-taken function, and replaces all references to the function
with the address of the jump table entry.
Note that because non-canonical jump table addresses are local
to each component, they break cross-module function address
equality. Specifically, the address of a global function will be
different in each module, as it's replaced with the address of a local
jump table entry. If this address is passed to a different module,
it won’t match the address of the same function taken there. This
may break code that relies on comparing addresses passed from other
components.
CFI checking can be disabled in a function with the __nocfi attribute.
Additionally, CFI can be disabled for an entire compilation unit by
filtering out CC_FLAGS_CFI.
By default, CFI failures result in a kernel panic to stop a potential
exploit. CONFIG_CFI_PERMISSIVE enables a permissive mode, where the
kernel prints out a rate-limited warning instead, and allows execution
to continue. This option is helpful for locating type mismatches, but
should only be enabled during development.
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210408182843.1754385-2-samitolvanen@google.com
This provides the ability for architectures to enable kernel stack base
address offset randomization. This feature is controlled by the boot
param "randomize_kstack_offset=on/off", with its default value set by
CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT.
This feature is based on the original idea from the last public release
of PaX's RANDKSTACK feature: https://pax.grsecurity.net/docs/randkstack.txt
All the credit for the original idea goes to the PaX team. Note that
the design and implementation of this upstream randomize_kstack_offset
feature differs greatly from the RANDKSTACK feature (see below).
Reasoning for the feature:
This feature aims to make harder the various stack-based attacks that
rely on deterministic stack structure. We have had many such attacks in
past (just to name few):
https://jon.oberheide.org/files/infiltrate12-thestackisback.pdfhttps://jon.oberheide.org/files/stackjacking-infiltrate11.pdfhttps://googleprojectzero.blogspot.com/2016/06/exploiting-recursion-in-linux-kernel_20.html
As Linux kernel stack protections have been constantly improving
(vmap-based stack allocation with guard pages, removal of thread_info,
STACKLEAK), attackers have had to find new ways for their exploits
to work. They have done so, continuing to rely on the kernel's stack
determinism, in situations where VMAP_STACK and THREAD_INFO_IN_TASK_STRUCT
were not relevant. For example, the following recent attacks would have
been hampered if the stack offset was non-deterministic between syscalls:
https://repositorio-aberto.up.pt/bitstream/10216/125357/2/374717.pdf
(page 70: targeting the pt_regs copy with linear stack overflow)
https://a13xp0p0v.github.io/2020/02/15/CVE-2019-18683.html
(leaked stack address from one syscall as a target during next syscall)
The main idea is that since the stack offset is randomized on each system
call, it is harder for an attack to reliably land in any particular place
on the thread stack, even with address exposures, as the stack base will
change on the next syscall. Also, since randomization is performed after
placing pt_regs, the ptrace-based approach[1] to discover the randomized
offset during a long-running syscall should not be possible.
Design description:
During most of the kernel's execution, it runs on the "thread stack",
which is pretty deterministic in its structure: it is fixed in size,
and on every entry from userspace to kernel on a syscall the thread
stack starts construction from an address fetched from the per-cpu
cpu_current_top_of_stack variable. The first element to be pushed to the
thread stack is the pt_regs struct that stores all required CPU registers
and syscall parameters. Finally the specific syscall function is called,
with the stack being used as the kernel executes the resulting request.
The goal of randomize_kstack_offset feature is to add a random offset
after the pt_regs has been pushed to the stack and before the rest of the
thread stack is used during the syscall processing, and to change it every
time a process issues a syscall. The source of randomness is currently
architecture-defined (but x86 is using the low byte of rdtsc()). Future
improvements for different entropy sources is possible, but out of scope
for this patch. Further more, to add more unpredictability, new offsets
are chosen at the end of syscalls (the timing of which should be less
easy to measure from userspace than at syscall entry time), and stored
in a per-CPU variable, so that the life of the value does not stay
explicitly tied to a single task.
As suggested by Andy Lutomirski, the offset is added using alloca()
and an empty asm() statement with an output constraint, since it avoids
changes to assembly syscall entry code, to the unwinder, and provides
correct stack alignment as defined by the compiler.
In order to make this available by default with zero performance impact
for those that don't want it, it is boot-time selectable with static
branches. This way, if the overhead is not wanted, it can just be
left turned off with no performance impact.
The generated assembly for x86_64 with GCC looks like this:
...
ffffffff81003977: 65 8b 05 02 ea 00 7f mov %gs:0x7f00ea02(%rip),%eax
# 12380 <kstack_offset>
ffffffff8100397e: 25 ff 03 00 00 and $0x3ff,%eax
ffffffff81003983: 48 83 c0 0f add $0xf,%rax
ffffffff81003987: 25 f8 07 00 00 and $0x7f8,%eax
ffffffff8100398c: 48 29 c4 sub %rax,%rsp
ffffffff8100398f: 48 8d 44 24 0f lea 0xf(%rsp),%rax
ffffffff81003994: 48 83 e0 f0 and $0xfffffffffffffff0,%rax
...
As a result of the above stack alignment, this patch introduces about
5 bits of randomness after pt_regs is spilled to the thread stack on
x86_64, and 6 bits on x86_32 (since its has 1 fewer bit required for
stack alignment). The amount of entropy could be adjusted based on how
much of the stack space we wish to trade for security.
My measure of syscall performance overhead (on x86_64):
lmbench: /usr/lib/lmbench/bin/x86_64-linux-gnu/lat_syscall -N 10000 null
randomize_kstack_offset=y Simple syscall: 0.7082 microseconds
randomize_kstack_offset=n Simple syscall: 0.7016 microseconds
So, roughly 0.9% overhead growth for a no-op syscall, which is very
manageable. And for people that don't want this, it's off by default.
There are two gotchas with using the alloca() trick. First,
compilers that have Stack Clash protection (-fstack-clash-protection)
enabled by default (e.g. Ubuntu[3]) add pagesize stack probes to
any dynamic stack allocations. While the randomization offset is
always less than a page, the resulting assembly would still contain
(unreachable!) probing routines, bloating the resulting assembly. To
avoid this, -fno-stack-clash-protection is unconditionally added to
the kernel Makefile since this is the only dynamic stack allocation in
the kernel (now that VLAs have been removed) and it is provably safe
from Stack Clash style attacks.
The second gotcha with alloca() is a negative interaction with
-fstack-protector*, in that it sees the alloca() as an array allocation,
which triggers the unconditional addition of the stack canary function
pre/post-amble which slows down syscalls regardless of the static
branch. In order to avoid adding this unneeded check and its associated
performance impact, architectures need to carefully remove uses of
-fstack-protector-strong (or -fstack-protector) in the compilation units
that use the add_random_kstack() macro and to audit the resulting stack
mitigation coverage (to make sure no desired coverage disappears). No
change is visible for this on x86 because the stack protector is already
unconditionally disabled for the compilation unit, but the change is
required on arm64. There is, unfortunately, no attribute that can be
used to disable stack protector for specific functions.
Comparison to PaX RANDKSTACK feature:
The RANDKSTACK feature randomizes the location of the stack start
(cpu_current_top_of_stack), i.e. including the location of pt_regs
structure itself on the stack. Initially this patch followed the same
approach, but during the recent discussions[2], it has been determined
to be of a little value since, if ptrace functionality is available for
an attacker, they can use PTRACE_PEEKUSR/PTRACE_POKEUSR to read/write
different offsets in the pt_regs struct, observe the cache behavior of
the pt_regs accesses, and figure out the random stack offset. Another
difference is that the random offset is stored in a per-cpu variable,
rather than having it be per-thread. As a result, these implementations
differ a fair bit in their implementation details and results, though
obviously the intent is similar.
[1] https://lore.kernel.org/kernel-hardening/2236FBA76BA1254E88B949DDB74E612BA4BC57C1@IRSMSX102.ger.corp.intel.com/
[2] https://lore.kernel.org/kernel-hardening/20190329081358.30497-1-elena.reshetova@intel.com/
[3] https://lists.ubuntu.com/archives/ubuntu-devel/2019-June/040741.html
Co-developed-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20210401232347.2791257-4-keescook@chromium.org
VPATH is used in Kbuild to make pattern rules search for prerequisites
in both $(objtree) and $(srctree). Some of *.c, *.S files are not real
sources, but generated by tools such as flex, bison, perl.
In contrast, I doubt the benefit of --include-dir=$(abs_srctree) because
it is always clear which Makefiles are real sources, and which are not.
So, my hope is to add $(srctree)/ prefix to all check-in Makefiles,
then remove --include-dir=$(abs_srctree) flag in the future.
I am touching only some Kbuild core parts for now. Treewide fixes will
be needed to achieve this goal.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Linus reported a build error due to the GCC plugin incompatibility
when the compiler is upgraded. [1]
GCC plugins are tied to a particular GCC version. So, they must be
rebuilt when the compiler is upgraded.
This seems to be a long-standing flaw since the initial support of
GCC plugins.
Extend commit 8b59cd81dc ("kbuild: ensure full rebuild when the
compiler is updated"), so that GCC plugins are covered by the
compiler upgrade detection.
[1]: https://lore.kernel.org/lkml/CAHk-=wieoN5ttOy7SnsGwZv+Fni3R6m-Ut=oxih6bbZ28G+4dw@mail.gmail.com/
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
'make image_name' needs include/config/auto.conf to show the correct
output because KBUILD_IMAGE depends on CONFIG options, but should not
attempt to resync the configuration.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Commit 78d3bb4483 ("kbuild: Fix <linux/version.h> for empty SUBLEVEL
or PATCHLEVEL") fixed the build error for empty SUBLEVEL or PATCHLEVEL
by prepending a zero.
Commit 9b82f13e7e ("kbuild: clamp SUBLEVEL to 255") re-introduced
this issue.
This time, we cannot take the same approach because we have C code:
#define LINUX_VERSION_PATCHLEVEL $(PATCHLEVEL)
#define LINUX_VERSION_SUBLEVEL $(SUBLEVEL)
Replace empty SUBLEVEL/PATCHLEVEL with a zero.
Fixes: 9b82f13e7e ("kbuild: clamp SUBLEVEL to 255")
Reported-by: Christian Zigotzky <chzigotzky@xenosoft.de>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-and-tested-by: Sasha Levin <sashal@kernel.org>
'make -s' should be really silent. However, 'make -s V=1' prints noisy
log messages from some shell scripts.
Of course, such a combination is odd, but the build system needs to do
the right thing even if a user gives strange input.
If -s is given, KBUILD_VERBOSE should be forced to 0.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Linus Torvalds