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: email@example.com # v3.15+
Fixes: 72b22bbad1e7 ("MIPS: Don't assume 64-bit FP registers for FP regset")
Signed-off-by: Maciej W. Rozycki <firstname.lastname@example.org>
New in v2.
arch/mips/kernel/ptrace.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
--- linux-sfr-test.orig/arch/mips/kernel/ptrace.c 2017-12-08
+++ linux-sfr-test/arch/mips/kernel/ptrace.c 2017-12-08 16:21:19.498382000
@@ -507,7 +507,15 @@ static int fpr_set_msa(struct task_struc
-/* 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
+ BUG_ON(count % sizeof(elf_fpreg_t));
/* XXX fcr31 */