The patch below does not apply to the 3.18-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From dc24d0edf33c3e15099688b6bbdf7bdc24bf6e91 Mon Sep 17 00:00:00 2001

From: "Maciej W. Rozycki" macro@mips.com Date: Mon, 11 Dec 2017 22:52:15 +0000 Subject: [PATCH] MIPS: Guard against any partial write attempt with PTRACE_SETREGSET

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

diff --git a/arch/mips/kernel/ptrace.c b/arch/mips/kernel/ptrace.c index 62e8ffd9370a..7fcadaaf330f 100644 --- a/arch/mips/kernel/ptrace.c +++ b/arch/mips/kernel/ptrace.c @@ -516,7 +516,15 @@ static int fpr_set_msa(struct task_struct *target, 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, @@ -524,6 +532,8 @@ static int fpr_set(struct task_struct *target, { int err;

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

init_fp_ctx(target);