[PATCH 4.4 30/42] arm64/ptrace: Preserve previous registers for short regset write

[Greg Kroah-Hartman]

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

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

From: Dave Martin <dave.mar...@arm.com>

commit 9a17b876b573441bfb3387ad55d98bf7184daf9d upstream.

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

Fixes: 478fcb2cdb23 ("arm64: Debugging support")
Signed-off-by: Dave Martin <dave.mar...@arm.com>
Acked-by: Will Deacon <will.dea...@arm.com>
Signed-off-by: Catalin Marinas <catalin.mari...@arm.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 arch/arm64/kernel/ptrace.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -495,7 +495,7 @@ static int gpr_set(struct task_struct *t
                   const void *kbuf, const void __user *ubuf)
 {
        int ret;
-       struct user_pt_regs newregs;
+       struct user_pt_regs newregs = task_pt_regs(target)->user_regs;
 
        ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &newregs, 0, -1);
        if (ret)
@@ -525,7 +525,8 @@ static int fpr_set(struct task_struct *t
                   const void *kbuf, const void __user *ubuf)
 {
        int ret;
-       struct user_fpsimd_state newstate;
+       struct user_fpsimd_state newstate =
+               target->thread.fpsimd_state.user_fpsimd;
 
        ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &newstate, 0, -1);
        if (ret)
@@ -549,7 +550,7 @@ static int tls_set(struct task_struct *t
                   const void *kbuf, const void __user *ubuf)
 {
        int ret;
-       unsigned long tls;
+       unsigned long tls = target->thread.tp_value;
 
        ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &tls, 0, -1);
        if (ret)