arm64/ptrace: Preserve previous registers for short regset write - 3

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@arm.com>
Acked-by: Will Deacon <Will.Deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[sw0312.kim: backport linux-4.9.y stable commit for better compat ptrace]
Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>
Change-Id: Iecc750ebece962708c77457c790b1ecdac69dee9

diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index f608b8ca5d2e0fc48e9f1806d04fdf80ccfb93fe..3eb848865d93cc4935dc4ce13429e78b3071ab57 100644 (file)
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -843,7 +843,7 @@ static int compat_tls_set(struct task_struct *target,
                          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)