[PATCH 4/5] MIPS: Execute any partial write of the last register with PTRACE_SETREGSET

[Maciej W. Rozycki]

Fix a commit d614fd58a283 ("mips/ptrace: Preserve previous registers for 
short regset write") bug and allow the last register requested with a 
ptrace(2) PTRACE_SETREGSET call to be partially written if supplied this 
way by the caller, like with other register sets.

Cc: stable@xxxxxxxxxxxxxxx # v4.11+
Fixes: d614fd58a283 ("mips/ptrace: Preserve previous registers for short regset write")
Signed-off-by: Maciej W. Rozycki <macro@xxxxxxxx>
---
 arch/mips/kernel/ptrace.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

linux-mips-nt-prfpreg-count.diff
Index: linux-sfr-test/arch/mips/kernel/ptrace.c
===================================================================
--- linux-sfr-test.orig/arch/mips/kernel/ptrace.c	2017-11-21 22:12:00.000000000 +0000
+++ linux-sfr-test/arch/mips/kernel/ptrace.c	2017-11-21 22:13:13.471970000 +0000
@@ -484,7 +484,7 @@ static int fpr_set_msa(struct task_struc
 	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));