powerpc/signal32: Perform access_ok() inside restore_user_regs()

In preparation of using user_access_begin/end in restore_user_regs(),
move the access_ok() inside the function.

It makes no difference as the behaviour on a failed access_ok() is
the same as on failed restore_user_regs().
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/c106eb2f37c3040f1fd38b40e50c670feb7cb835.1616151715.git.christophe.leroy@csgroup.eu

arch/powerpc/kernel/signal_32.c

@@ -492,6 +492,8 @@ static long restore_user_regs(struct pt_regs *regs,
 	int i;
 #endif
 
+	if (!access_ok(sr, sizeof(*sr)))
+		return 1;
 	/*
 	 * restore general registers but not including MSR or SOFTE. Also
 	 * take care of keeping r2 (TLS) intact if not a signal
@@ -963,13 +965,10 @@ static int do_setcontext(struct ucontext __user *ucp, struct pt_regs *regs, int
 		if (__get_user(cmcp, &ucp->uc_regs))
 			return -EFAULT;
 		mcp = (struct mcontext __user *)(u64)cmcp;
-		/* no need to check access_ok(mcp), since mcp < 4GB */
 	}
 #else
 	if (__get_user(mcp, &ucp->uc_regs))
 		return -EFAULT;
-	if (!access_ok(mcp, sizeof(*mcp)))
-		return -EFAULT;
 #endif
 	set_current_blocked(&set);
 	if (restore_user_regs(regs, mcp, sig))
@@ -1362,8 +1361,7 @@ SYSCALL_DEFINE0(sigreturn)
 	} else {
 		sr = (struct mcontext __user *)from_user_ptr(sigctx.regs);
 		addr = sr;
-		if (!access_ok(sr, sizeof(*sr))
-		    || restore_user_regs(regs, sr, 1))
+		if (restore_user_regs(regs, sr, 1))
 			goto badframe;
 	}