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 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 */
> ---
> 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);
>
