arm64/ptrace: Preserve previous registers for short regset write - 2

commit 9dd73f72f218320c6c90da5f834996e7360dc227 upstream.

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

Fixes: 766a85d7bc5d ("arm64: ptrace: add NT_ARM_SYSTEM_CALL regset")
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: Ibc586abfaf04a3466cdb093f1f76962c8071f797

diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index 185dd69e44c120d3dbd35a1f7f535fc533eeccb6..f608b8ca5d2e0fc48e9f1806d04fdf80ccfb93fe 100644 (file)
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -570,7 +570,8 @@ static int system_call_set(struct task_struct *target,
                           unsigned int pos, unsigned int count,
                           const void *kbuf, const void __user *ubuf)
 {
-       int syscallno, ret;
+       int syscallno = task_pt_regs(target)->syscallno;
+       int ret;
 
        ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &syscallno, 0, -1);
        if (ret)