[PATCH 4.9 072/130] arm64/ptrace: Preserve previous registers for short regset write - 3

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dave Martin <Dave.Martin@xxxxxxx>

commit a672401c00f82e4e19704aff361d9bad18003714 upstream.

Ensure that if userspace supplies insufficient data to
PTRACE_SETREGSET to fill all the registers, the thread's old
registers are preserved.

Fixes: 5d220ff9420f ("arm64: Better native ptrace support for compat tasks")
Signed-off-by: Dave Martin <Dave.Martin@xxxxxxx>
Acked-by: Will Deacon <Will.Deacon@xxxxxxx>
Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 arch/arm64/kernel/ptrace.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -949,7 +949,7 @@ static int compat_tls_set(struct task_st
 			  const void __user *ubuf)
 {
 	int ret;
-	compat_ulong_t tls;
+	compat_ulong_t tls = target->thread.tp_value;
 
 	ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &tls, 0, -1);
 	if (ret)