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powerpc/signal32: Use struct_group() to zero spe regs

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In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memset(), avoid intentionally writing across
neighboring fields.

Add a struct_group() for the spe registers so that memset() can correctly reason
about the size:

   In function 'fortify_memset_chk',
       inlined from 'restore_user_regs.part.0' at arch/powerpc/kernel/signal_32.c:539:3:
   >> include/linux/fortify-string.h:195:4: error: call to '__write_overflow_field' declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror=attribute-warning]
     195 |    __write_overflow_field();
         |    ^~~~~~~~~~~~~~~~~~~~~~~~

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211118203604.1288379-1-keescook@chromium.org
This commit is contained in:
Kees Cook 2021-11-18 12:36:04 -08:00 committed by Michael Ellerman
parent af11dee436
commit 62ea67e319
2 changed files with 13 additions and 7 deletions
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6
arch/powerpc/include/asm/processor.h
View file

@ -191,8 +191,10 @@ struct thread_struct {
int used_vsr; /* set if process has used VSX */
#endif /* CONFIG_VSX */
#ifdef CONFIG_SPE
unsigned long evr[32]; /* upper 32-bits of SPE regs */
u64 acc; /* Accumulator */
struct_group(spe,
unsigned long evr[32]; /* upper 32-bits of SPE regs */
u64 acc; /* Accumulator */
);
unsigned long spefscr; /* SPE & eFP status */
unsigned long spefscr_last; /* SPEFSCR value on last prctl
call or trap return */

14
arch/powerpc/kernel/signal_32.c
View file

@ -527,16 +527,20 @@ static long restore_user_regs(struct pt_regs *regs,
regs_set_return_msr(regs, regs->msr & ~(MSR_FP | MSR_FE0 | MSR_FE1));
#ifdef CONFIG_SPE
/* force the process to reload the spe registers from
current->thread when it next does spe instructions */
/*
* Force the process to reload the spe registers from
* current->thread when it next does spe instructions.
* Since this is user ABI, we must enforce the sizing.
*/
BUILD_BUG_ON(sizeof(current->thread.spe) != ELF_NEVRREG * sizeof(u32));
regs_set_return_msr(regs, regs->msr & ~MSR_SPE);
if (msr & MSR_SPE) {
/* restore spe registers from the stack */
unsafe_copy_from_user(current->thread.evr, &sr->mc_vregs,
ELF_NEVRREG * sizeof(u32), failed);
unsafe_copy_from_user(&current->thread.spe, &sr->mc_vregs,
sizeof(current->thread.spe), failed);
current->thread.used_spe = true;
} else if (current->thread.used_spe)
memset(current->thread.evr, 0, ELF_NEVRREG * sizeof(u32));
memset(&current->thread.spe, 0, sizeof(current->thread.spe));
/* Always get SPEFSCR back */
unsafe_get_user(current->thread.spefscr, (u32 __user *)&sr->mc_vregs + ELF_NEVRREG, failed);