powerpc/signal32: Use struct_group() to zero spe regs

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 <lkp@intel.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211118203604.1288379-1-keescook@chromium.org

diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h
index e39bd0f..978a803 100644 (file)
--- 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 3e053e2..d84c434 100644 (file)
--- 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(&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);