MIPS: Consistently handle buffer counter with PTRACE_SETREGSET

commit 80b3ffce0196ea50068885d085ff981e4b8396f4 upstream.

Update commit d614fd58a283 ("mips/ptrace: Preserve previous registers
for short regset write") bug and consistently consume all data supplied
to `fpr_set_msa' with the ptrace(2) PTRACE_SETREGSET request, such that
a zero data buffer counter is returned where insufficient data has been
given to fill a whole number of FP general registers.

In reality this is not going to happen, as the caller is supposed to
only supply data covering a whole number of registers and it is verified
in `ptrace_regset' and again asserted in `fpr_set', however structuring
code such that the presence of trailing partial FP general register data
causes `fpr_set_msa' to return with a non-zero data buffer counter makes
it appear that this trailing data will be used if there are subsequent
writes made to FP registers, which is going to be the case with the FCSR
once the missing write to that register has been fixed.

Fixes: d614fd58a283 ("mips/ptrace: Preserve previous registers for short regset write")
Signed-off-by: Maciej W. Rozycki <macro@mips.com>
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
Patchwork: https://patchwork.linux-mips.org/patch/17927/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/mips/kernel/ptrace.c b/arch/mips/kernel/ptrace.c
index 7aefd81966812f81b93e990a27da2fa0e205e602..3c5e0446b28dd545d0377ae36fc3ea15a98fb47d 100644 (file)
--- a/arch/mips/kernel/ptrace.c
+++ b/arch/mips/kernel/ptrace.c
@@ -495,7 +495,7 @@ static int fpr_set_msa(struct task_struct *target,
        int err;
 
        BUILD_BUG_ON(sizeof(fpr_val) != sizeof(elf_fpreg_t));
-       for (i = 0; i < NUM_FPU_REGS && *count >= sizeof(elf_fpreg_t); i++) {
+       for (i = 0; i < NUM_FPU_REGS && *count > 0; i++) {
                err = user_regset_copyin(pos, count, kbuf, ubuf,
                                         &fpr_val, i * sizeof(elf_fpreg_t),
                                         (i + 1) * sizeof(elf_fpreg_t));