An intrinsic for an old instruction, as described in the Intel SDM.
Reviewers: craig.topper, rnk
Reviewed By: craig.topper, rnk
Differential Revision: https://reviews.llvm.org/D47142
llvm-svn: 333256
in gcc by https://gcc.gnu.org/ml/gcc-cvs/2018-04/msg00534.html.
The -mibt feature flag is being removed, and the -fcf-protection
option now also defines a CET macro and causes errors when used
on non-X86 targets, while X86 targets no longer check for -mibt
and -mshstk to determine if -fcf-protection is supported. -mshstk
is now used only to determine availability of shadow stack intrinsics.
Comes with an LLVM patch (D46882).
Patch by mike.dvoretsky
Differential Revision: https://reviews.llvm.org/D46881
llvm-svn: 332704
The WBNOINVD instruction writes back all modified
cache lines in the processor’s internal cache to main memory
but does not invalidate (flush) the internal caches.
Reviewers: craig.topper, zvi, ashlykov
Reviewed By: craig.topper
Differential Revision: https://reviews.llvm.org/D43817
llvm-svn: 329848
Found via codespell -q 3 -I ../clang-whitelist.txt
Where whitelist consists of:
archtype
cas
classs
checkk
compres
definit
frome
iff
inteval
ith
lod
methode
nd
optin
ot
pres
statics
te
thru
Patch by luzpaz! (This is a subset of D44188 that applies cleanly with a few
files that have dubious fixes reverted.)
Differential revision: https://reviews.llvm.org/D44188
llvm-svn: 329399
Cannon Lake does not support CLWB, therefore it
does not include all features listed under SKX.
Patch by Gabor Buella
Differential Revision: https://reviews.llvm.org/D43459
llvm-svn: 325655
Summary:
Make clang accept `-msahf` (and `-mno-sahf`) flags to activate the
`+sahf` feature for the backend, for bug 36028 (Incorrect use of
pushf/popf enables/disables interrupts on amd64 kernels). This was
originally submitted in bug 36037 by Jonathan Looney
<jonlooney@gmail.com>.
As described there, GCC also uses `-msahf` for this feature, and the
backend already recognizes the `+sahf` feature. All that is needed is to
teach clang to pass this on to the backend.
The mapping of feature support onto CPUs may not be complete; rather, it
was chosen to match LLVM's idea of which CPUs support this feature (see
lib/Target/X86/X86.td).
I also updated the affected test case (CodeGen/attr-target-x86.c) to
match the emitted output.
Reviewers: craig.topper, coby, efriedma, rsmith
Reviewed By: craig.topper
Subscribers: emaste, cfe-commits
Differential Revision: https://reviews.llvm.org/D43394
llvm-svn: 325446
Summary:
First, we need to explain the core of the vulnerability. Note that this
is a very incomplete description, please see the Project Zero blog post
for details:
https://googleprojectzero.blogspot.com/2018/01/reading-privileged-memory-with-side.html
The basis for branch target injection is to direct speculative execution
of the processor to some "gadget" of executable code by poisoning the
prediction of indirect branches with the address of that gadget. The
gadget in turn contains an operation that provides a side channel for
reading data. Most commonly, this will look like a load of secret data
followed by a branch on the loaded value and then a load of some
predictable cache line. The attacker then uses timing of the processors
cache to determine which direction the branch took *in the speculative
execution*, and in turn what one bit of the loaded value was. Due to the
nature of these timing side channels and the branch predictor on Intel
processors, this allows an attacker to leak data only accessible to
a privileged domain (like the kernel) back into an unprivileged domain.
The goal is simple: avoid generating code which contains an indirect
branch that could have its prediction poisoned by an attacker. In many
cases, the compiler can simply use directed conditional branches and
a small search tree. LLVM already has support for lowering switches in
this way and the first step of this patch is to disable jump-table
lowering of switches and introduce a pass to rewrite explicit indirectbr
sequences into a switch over integers.
However, there is no fully general alternative to indirect calls. We
introduce a new construct we call a "retpoline" to implement indirect
calls in a non-speculatable way. It can be thought of loosely as
a trampoline for indirect calls which uses the RET instruction on x86.
Further, we arrange for a specific call->ret sequence which ensures the
processor predicts the return to go to a controlled, known location. The
retpoline then "smashes" the return address pushed onto the stack by the
call with the desired target of the original indirect call. The result
is a predicted return to the next instruction after a call (which can be
used to trap speculative execution within an infinite loop) and an
actual indirect branch to an arbitrary address.
On 64-bit x86 ABIs, this is especially easily done in the compiler by
using a guaranteed scratch register to pass the target into this device.
For 32-bit ABIs there isn't a guaranteed scratch register and so several
different retpoline variants are introduced to use a scratch register if
one is available in the calling convention and to otherwise use direct
stack push/pop sequences to pass the target address.
This "retpoline" mitigation is fully described in the following blog
post: https://support.google.com/faqs/answer/7625886
We also support a target feature that disables emission of the retpoline
thunk by the compiler to allow for custom thunks if users want them.
These are particularly useful in environments like kernels that
routinely do hot-patching on boot and want to hot-patch their thunk to
different code sequences. They can write this custom thunk and use
`-mretpoline-external-thunk` *in addition* to `-mretpoline`. In this
case, on x86-64 thu thunk names must be:
```
__llvm_external_retpoline_r11
```
or on 32-bit:
```
__llvm_external_retpoline_eax
__llvm_external_retpoline_ecx
__llvm_external_retpoline_edx
__llvm_external_retpoline_push
```
And the target of the retpoline is passed in the named register, or in
the case of the `push` suffix on the top of the stack via a `pushl`
instruction.
There is one other important source of indirect branches in x86 ELF
binaries: the PLT. These patches also include support for LLD to
generate PLT entries that perform a retpoline-style indirection.
The only other indirect branches remaining that we are aware of are from
precompiled runtimes (such as crt0.o and similar). The ones we have
found are not really attackable, and so we have not focused on them
here, but eventually these runtimes should also be replicated for
retpoline-ed configurations for completeness.
For kernels or other freestanding or fully static executables, the
compiler switch `-mretpoline` is sufficient to fully mitigate this
particular attack. For dynamic executables, you must compile *all*
libraries with `-mretpoline` and additionally link the dynamic
executable and all shared libraries with LLD and pass `-z retpolineplt`
(or use similar functionality from some other linker). We strongly
recommend also using `-z now` as non-lazy binding allows the
retpoline-mitigated PLT to be substantially smaller.
When manually apply similar transformations to `-mretpoline` to the
Linux kernel we observed very small performance hits to applications
running typical workloads, and relatively minor hits (approximately 2%)
even for extremely syscall-heavy applications. This is largely due to
the small number of indirect branches that occur in performance
sensitive paths of the kernel.
When using these patches on statically linked applications, especially
C++ applications, you should expect to see a much more dramatic
performance hit. For microbenchmarks that are switch, indirect-, or
virtual-call heavy we have seen overheads ranging from 10% to 50%.
However, real-world workloads exhibit substantially lower performance
impact. Notably, techniques such as PGO and ThinLTO dramatically reduce
the impact of hot indirect calls (by speculatively promoting them to
direct calls) and allow optimized search trees to be used to lower
switches. If you need to deploy these techniques in C++ applications, we
*strongly* recommend that you ensure all hot call targets are statically
linked (avoiding PLT indirection) and use both PGO and ThinLTO. Well
tuned servers using all of these techniques saw 5% - 10% overhead from
the use of retpoline.
We will add detailed documentation covering these components in
subsequent patches, but wanted to make the core functionality available
as soon as possible. Happy for more code review, but we'd really like to
get these patches landed and backported ASAP for obvious reasons. We're
planning to backport this to both 6.0 and 5.0 release streams and get
a 5.0 release with just this cherry picked ASAP for distros and vendors.
This patch is the work of a number of people over the past month: Eric, Reid,
Rui, and myself. I'm mailing it out as a single commit due to the time
sensitive nature of landing this and the need to backport it. Huge thanks to
everyone who helped out here, and everyone at Intel who helped out in
discussions about how to craft this. Also, credit goes to Paul Turner (at
Google, but not an LLVM contributor) for much of the underlying retpoline
design.
Reviewers: echristo, rnk, ruiu, craig.topper, DavidKreitzer
Subscribers: sanjoy, emaste, mcrosier, mgorny, mehdi_amini, hiraditya, llvm-commits
Differential Revision: https://reviews.llvm.org/D41723
llvm-svn: 323155
Similarly, make -mno-fma and -mno-f16c imply -mno-avx512f.
Withou this "-mno-sse -mavx512f" ends up with avx512f being enabled in the frontend but disabled in the backend.
llvm-svn: 322245
Cf-protection is a target independent flag that instructs the back-end to instrument control flow mechanisms like: Branch, Return, etc.
For example in X86 this flag will be used to instrument Indirect Branch Tracking instructions.
Differential Revision: https://reviews.llvm.org/D40478
Change-Id: I5126e766c0e6b84118cae0ee8a20fe78cc373dea
llvm-svn: 322063
GCC's attribute 'target', in addition to being an optimization hint,
also allows function multiversioning. We currently have the former
implemented, this is the latter's implementation.
This works by enabling functions with the same name/signature to coexist,
so that they can all be emitted. Multiversion state is stored in the
FunctionDecl itself, and SemaDecl manages the definitions.
Note that it ends up having to permit redefinition of functions so
that they can all be emitted. Additionally, all versions of the function
must be emitted, so this also manages that.
Note that this includes some additional rules that GCC does not, since
defining something as a MultiVersion function after a usage has been made illegal.
The only 'history rewriting' that happens is if a function is emitted before
it has been converted to a multiversion'ed function, at which point its name
needs to be changed.
Function templates and virtual functions are NOT yet supported (not supported
in GCC either).
Additionally, constructors/destructors are disallowed, but the former is
planned.
llvm-svn: 322028
I based that commit on what was in Intel's public documentation here https://software.intel.com/sites/default/files/managed/c5/15/architecture-instruction-set-extensions-programming-reference.pdf
Which specifically said CLWB wasn't until Icelake.
But I've since cross checked with SDE and it thinks these features exist on CNL and ICL. So now I don't know what to believe.
I've added test coverage of the current behavior as part of the revert so at least now have proof of what we're doing.
llvm-svn: 321547
We have cannonlake and icelake inheriting from skylake server in a switch using fallthroughs. But they aren't perfect supersets of skylake server.
llvm-svn: 321504
added vbmi2 feature recognition
added intrinsics support for vbmi2 instructions
_mm[128,256,512]_mask[z]_compress_epi[16,32]
_mm[128,256,512]_mask_compressstoreu_epi[16,32]
_mm[128,256,512]_mask[z]_expand_epi[16,32]
_mm[128,256,512]_mask[z]_expandloadu_epi[16,32]
_mm[128,256,512]_mask[z]_sh[l,r]di_epi[16,32,64]
_mm[128,256,512]_mask_sh[l,r]dv_epi[16,32,64]
matching a similar work on the backend (D40206)
Differential Revision: https://reviews.llvm.org/D41557
llvm-svn: 321487
added vpclmulqdq feature recognition
added intrinsics support for vpclmulqdq instructions
_mm256_clmulepi64_epi128
_mm512_clmulepi64_epi128
matching a similar work on the backend (D40101)
Differential Revision: https://reviews.llvm.org/D41573
llvm-svn: 321480
added vaes feature recognition
added intrinsics support for vaes instructions, matching a similar work on the backend (D40078)
_mm256_aesenc_epi128
_mm512_aesenc_epi128
_mm256_aesenclast_epi128
_mm512_aesenclast_epi128
_mm256_aesdec_epi128
_mm512_aesdec_epi128
_mm256_aesdeclast_epi128
_mm512_aesdeclast_epi128
llvm-svn: 321474
https://bugs.llvm.org/show_bug.cgi?id=35721 reports that x86intrin.h
is issuing a few warnings. This is because attribute target is using
isValidFeatureName for its source. It was also discovered that two of
these were missing from hasFeature.
Additionally, shstk is and ibu are reordered alphabetically, as came
up during code review.
llvm-svn: 321324
Shadow stack solution introduces a new stack for return addresses only.
The stack has a Shadow Stack Pointer (SSP) that points to the last address to which we expect to return.
If we return to a different address an exception is triggered.
This patch includes shadow stack intrinsics as well as the corresponding CET header.
It includes CET clang flags for shadow stack and Indirect Branch Tracking.
For more information, please see the following:
https://software.intel.com/sites/default/files/managed/4d/2a/control-flow-enforcement-technology-preview.pdf
Differential Revision: https://reviews.llvm.org/D40224
Change-Id: I79ad0925a028bbc94c8ecad75f6daa2f214171f1
llvm-svn: 318995
A first step toward removing the repetition of
features/CPU info in the x86 target info, this
patch pulls all the processor information out into
its own .def file.
Differential Revision: https://reviews.llvm.org/D40093
llvm-svn: 318343
LLVM exposes a file in the backend (X86TargetParser.def) that
contains information about the correct list of CpuIs values.
This patch removes 2 of the copied and pasted versions of this
list from clang and instead includes the data from the .def file.
Differential Revision: https://reviews.llvm.org/D40054
llvm-svn: 318234
Craig noticed that CodeGen wasn't properly ignoring the
values sent to the target attribute. This patch ignores
them.
This patch also sets the 'default' for this checking to
'supported', since only X86 has implemented the support
for checking valid CPU names and Feature Names.
One test was changed to i686, since it uses a lakemont,
which would otherwise be prohibited in x86_64.
Differential Revision: https://reviews.llvm.org/D39357
llvm-svn: 316783
These are not valid values for this, and are pretty
non-sensical, since LLVM doesn't understand them.
Differential Revision: https://reviews.llvm.org/D39378
llvm-svn: 316781
I think the only reason they are different is because we don't set tune_i686 for -march=i686 to match GCC. But GCC 4.9.0 seems to have changed this behavior and they do set it now. So I think they can aliases now.
Differential Revision: https://reviews.llvm.org/D39349
llvm-svn: 316712
As indicated by Table 1-1 in Intel Architecture Instruction Set Extensions and Future Features Programming Reference from October 2017.
llvm-svn: 316593
Gabor Buella