On Fri, Nov 19, 2021 at 08:46:27AM +0000, LEROY Christophe wrote:
>
>
> Le 18/11/2021 à 21:36, Kees Cook a écrit :
> > 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 <l...@intel.com>
> > Signed-off-by: Kees Cook <keesc...@chromium.org>
>
> Reviewed-by: Christophe Leroy <christophe.le...@csgroup.eu>
>
> However, is it really worth adding that grouping ? Wouldn't it be
> cleaner to handle evr[] and acc separately ? Now that we are using
> unsafe variants of get/put user performance wouldn't be impacted.
I'm fine with whatever is desired here. I reworked an earlier version of
this patch based on mpe's feedback, so I can certain rework it again. :)
>
> I have some doubts about things like:
>
> unsafe_copy_to_user(&frame->mc_vregs, current->thread.evr,
> ELF_NEVRREG * sizeof(u32), failed);
>
> Because as far as I can see, ELF_NEVRREG is 34 but mc_vregs is a table
> of 33 u32 and is at the end of the structure:
>
> struct mcontext {
> elf_gregset_t mc_gregs;
> elf_fpregset_t mc_fregs;
> unsigned long mc_pad[2];
> elf_vrregset_t mc_vregs __attribute__((__aligned__(16)));
> };
>
> typedef elf_vrreg_t elf_vrregset_t[ELF_NVRREG];
>
> # define ELF_NEVRREG 34 /* includes acc (as 2) */
> # define ELF_NVRREG 33 /* includes vscr */
I don't know these internals very well -- do you want me to change this
specifically somehow? With the BUILD_BUG_ON()s added, there's no binary
change here -- I wanted to make sure nothing was different in the
output.
-Kees
>
>
>
> > ---
> > arch/powerpc/include/asm/processor.h | 6 ++++--
> > arch/powerpc/kernel/signal_32.c | 14 +++++++++-----
> > 2 files changed, 13 insertions(+), 7 deletions(-)
> >
> > diff --git a/arch/powerpc/include/asm/processor.h
> > b/arch/powerpc/include/asm/processor.h
> > index e39bd0ff69f3..978a80308466 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 00a9c9cd6d42..5e1664b501e4 100644
> > --- a/arch/powerpc/kernel/signal_32.c
> > +++ b/arch/powerpc/kernel/signal_32.c
> > @@ -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(¤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);
> >
--
Kees Cook
