[PATCH v2 57/63] powerpc/signal32: Use struct_group() to zero spe regs

Kees Cook
2021-08-18T06:24:34Z

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();
| ^~~~~~~~~~~~~~~~~~~~~~~~

Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Sudeep Holla <sudeep.holla@arm.com>
Cc: linuxppc-dev@lists.ozlabs.org
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
---
arch/powerpc/include/asm/processor.h | 6 ++++--
arch/powerpc/kernel/signal_32.c | 6 +++---
2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h
index f348e564f7dd..05dc567cb9a8 100644
--- a/arch/powerpc/include/asm/processor.h
+++ b/arch/powerpc/include/asm/processor.h
@@ -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 */
diff --git a/arch/powerpc/kernel/signal_32.c b/arch/powerpc/kernel/signal_32.c
index 0608581967f0..77b86caf5c51 100644
--- a/arch/powerpc/kernel/signal_32.c
+++ b/arch/powerpc/kernel/signal_32.c
@@ -532,11 +532,11 @@ static long restore_user_regs(struct pt_regs *regs,
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);
--
2.30.2