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x86/head/64: Disable stack protection for head$(BITS).o 

On 64-bit, the startup_64_setup_env() function added in

  866b556efa ("x86/head/64: Install startup GDT")

has stack protection enabled because of set_bringup_idt_handler().
This happens when CONFIG_STACKPROTECTOR_STRONG is enabled. It
also currently needs CONFIG_AMD_MEM_ENCRYPT enabled because then
set_bringup_idt_handler() is not an empty stub but that might change in
the future, when the other vendor adds their similar technology.

At this point, %gs is not yet initialized, and this doesn't cause a
crash only because the #PF handler from the decompressor stub is still
installed and handles the page fault.

Disable stack protection for the whole file, and do it on 32-bit as
well to avoid surprises.

 [ bp: Extend commit message with the exact explanation how it happens. ]

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Joerg Roedel <jroedel@suse.de>
Link: https://lkml.kernel.org/r/20201008191623.2881677-6-nivedita@alum.mit.edu
This commit is contained in:
Arvind Sankar 2020-10-08 15:16:23 -04:00 committed by Borislav Petkov
parent e5ceb9a024
commit 103a4908ad
1 changed files with 2 additions and 0 deletions
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2
arch/x86/kernel/Makefile
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@ -47,6 +47,8 @@ endif
# non-deterministic coverage. # non-deterministic coverage.
KCOV_INSTRUMENT := n KCOV_INSTRUMENT := n
CFLAGS_head$(BITS).o += -fno-stack-protector
CFLAGS_irq.o := -I $(srctree)/$(src)/../include/asm/trace CFLAGS_irq.o := -I $(srctree)/$(src)/../include/asm/trace
obj-y := process_$(BITS).o signal.o obj-y := process_$(BITS).o signal.o