Messages in this thread | | | Subject | Re: [PATCH v2 57/63] powerpc/signal32: Use struct_group() to zero spe regs | From | Christophe Leroy <> | Date | Fri, 20 Aug 2021 09:53:41 +0200 |
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Le 20/08/2021 à 09:49, Michael Ellerman a écrit : > Kees Cook <keescook@chromium.org> writes: >> 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(¤t->thread.spe, &sr->mc_vregs, >> + sizeof(current->thread.spe), failed); > > This makes me nervous, because the ABI is that we copy ELF_NEVRREG * > sizeof(u32) bytes, not whatever sizeof(current->thread.spe) happens to > be. > > ie. if we use sizeof an inadvertent change to the fields in > thread_struct could change how many bytes we copy out to userspace, > which would be an ABI break. > > And that's not that hard to do, because it's not at all obvious that the > size and layout of fields in thread_struct affects the user ABI. > > At the same time we don't want to copy the right number of bytes but > the wrong content, so from that point of view using sizeof is good :) > > The way we handle it in ptrace is to have BUILD_BUG_ON()s to verify that > things match up, so maybe we should do that here too. > > ie. add: > > BUILD_BUG_ON(sizeof(current->thread.spe) == ELF_NEVRREG * sizeof(u32));
You mean != I guess ?
> > > Not sure if you are happy doing that as part of this patch. I can always > do it later if not. > > cheers >
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