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: stable@vger.kernel.org # v3.15+ Fixes: 72b22bbad1e7 ("MIPS: Don't assume 64-bit FP registers for FP regset") Signed-off-by: Maciej W. Rozycki macro@mips.com ---
New in v2.
--- arch/mips/kernel/ptrace.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-)
linux-mips-nt-prfpreg-size-bug.diff Index: linux-sfr-test/arch/mips/kernel/ptrace.c =================================================================== --- linux-sfr-test.orig/arch/mips/kernel/ptrace.c 2017-12-08 16:21:09.783307000 +0000 +++ linux-sfr-test/arch/mips/kernel/ptrace.c 2017-12-08 16:21:19.498382000 +0000 @@ -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);