===================================================================
@@ -507,7 +507,15 @@ static int fpr_set_msa(struct task_struc
return 0;
}
-/* Copy the supplied NT_PRFPREG buffer to the floating-point context. */
+/*
+ * Copy the supplied NT_PRFPREG buffer to the floating-point context.
+ *
+ * We optimize for the case where `count % sizeof(elf_fpreg_t) == 0',
+ * which is supposed to have been guaranteed by the kernel before
+ * calling us, e.g. in `ptrace_regset'. We enforce that requirement,
+ * so that we can safely avoid preinitializing temporaries for
+ * partial register writes.
+ */
static int fpr_set(struct task_struct *target,
const struct user_regset *regset,
unsigned int pos, unsigned int count,
@@ -515,6 +523,8 @@ static int fpr_set(struct task_struct *t
{
int err;
+ BUG_ON(count % sizeof(elf_fpreg_t));
+
/* XXX fcr31 */
init_fp_ctx(target);
Complement commit d614fd58a283 ("mips/ptrace: Preserve previous registers for short regset write") and ensure that no partial register write attempt is made with PTRACE_SETREGSET, as we do not preinitialize any temporaries used to hold incoming register data and consequently random data could be written. It is the responsibility of the caller, such as `ptrace_regset', to arrange for writes to span whole registers only, so here we only assert that it has indeed happened. Cc: # v3.15+ Fixes: 72b22bbad1e7 ("MIPS: Don't assume 64-bit FP registers for FP regset") Signed-off-by: Maciej W. Rozycki <> --- New in v2. --- arch/mips/kernel/ptrace.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) linux-mips-nt-prfpreg-size-bug.diff