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.

Signed-off-by: Maciej W. Rozycki macro@mips.com Fixes: 72b22bbad1e7 ("MIPS: Don't assume 64-bit FP registers for FP regset") Cc: James Hogan james.hogan@mips.com Cc: Paul Burton Paul.Burton@mips.com Cc: Alex Smith alex@alex-smith.me.uk Cc: Dave Martin Dave.Martin@arm.com Cc: linux-mips@linux-mips.org Cc: linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org # v3.15+ Patchwork: https://patchwork.linux-mips.org/patch/17926/ Signed-off-by: Ralf Baechle ralf@linux-mips.org --- Hi,

This is a (mechanically regenerated) version of commit dc24d0edf33c for 3.18-stable and before. No functional changes. Please apply.

Maciej

--- arch/mips/kernel/ptrace.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-)

linux-mips-nt-prfpreg-size-bug.diff Index: linux-stable-el/arch/mips/kernel/ptrace.c =================================================================== --- linux-stable-el.orig/arch/mips/kernel/ptrace.c 2018-01-10 20:13:31.900045000 +0000 +++ linux-stable-el/arch/mips/kernel/ptrace.c 2018-01-10 20:13:33.337064000 +0000 @@ -497,7 +497,15 @@ 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, @@ -505,6 +513,8 @@ static int fpr_set(struct task_struct *t { int err;

+ BUG_ON(count % sizeof(elf_fpreg_t)); + /* XXX fcr31 */

if (sizeof(target->thread.fpu.fpr[0]) == sizeof(elf_fpreg_t))