[PATCH AUTOSEL for 4.9 181/293] arm64: ptrace: Fix incorrect get_user() use in compat_vfp_set()

[Sasha Levin]

From: Dave Martin <Dave.Martin@xxxxxxx>

[ Upstream commit 5fbd5fc49fc39ac8433da62d16682a1d0217ea4f ]

Now that compat_vfp_get() uses the regset API to copy the FPSCR
value out to userspace, compat_vfp_set() looks inconsistent.  In
particular, compat_vfp_set() will fail if called with kbuf != NULL
&& ubuf == NULL (which is valid usage according to the regset API).

This patch fixes compat_vfp_set() to use user_regset_copyin(),
similarly to compat_vfp_get().

This also squashes a sparse warning triggered by the cast that
drops __user when calling get_user().

Signed-off-by: Dave Martin <Dave.Martin@xxxxxxx>
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
---
 arch/arm64/kernel/ptrace.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index cca95e75aaeb..df1addf104f5 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -926,18 +926,20 @@ static int compat_vfp_set(struct task_struct *target,
 {
 	struct user_fpsimd_state *uregs;
 	compat_ulong_t fpscr;
-	int ret;
+	int ret, vregs_end_pos;
 
 	if (pos + count > VFP_STATE_SIZE)
 		return -EIO;
 
 	uregs = &target->thread.fpsimd_state.user_fpsimd;
 
+	vregs_end_pos = VFP_STATE_SIZE - sizeof(compat_ulong_t);
 	ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, uregs, 0,
-				 VFP_STATE_SIZE - sizeof(compat_ulong_t));
+				 vregs_end_pos);
 
 	if (count && !ret) {
-		ret = get_user(fpscr, (compat_ulong_t *)ubuf);
+		ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &fpscr,
+					 vregs_end_pos, VFP_STATE_SIZE);
 		if (!ret) {
 			uregs->fpsr = fpscr & VFP_FPSCR_STAT_MASK;
 			uregs->fpcr = fpscr & VFP_FPSCR_CTRL_MASK;
-- 
2.15.1