| Message ID | 20210818060533.3569517-58-keescook@chromium.org |
|---|---|
| State | New |
| Headers | show |
| Series | Introduce strict memcpy() bounds checking | expand |
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 >
Kees Cook <keescook@chromium.org> writes: > On Fri, Aug 20, 2021 at 05:49:35PM +1000, Michael Ellerman wrote: >> 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)); >> >> Not sure if you are happy doing that as part of this patch. I can always >> do it later if not. > > Sounds good to me; I did that in a few other cases in the series where > the relationships between things seemed tenuous. :) I'll add this (as > !=) in v3. Thanks. cheers
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); current->thread.used_spe = true; } else if (current->thread.used_spe) - memset(current->thread.evr, 0, ELF_NEVRREG * sizeof(u32)); + memset(¤t->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);
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(-)