arm64: compat: Don't pull syscall number from regs in arm_compat_syscall

The syscall number may have been changed by a tracer, so we should pass
the actual number in from the caller instead of pulling it from the
saved r7 value directly.

Cc: <stable@vger.kernel.org>
Cc: Pi-Hsun Shih <pihsun@chromium.org>
Reviewed-by: Dave Martin <Dave.Martin@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/kernel/sys_compat.c

@@ -66,12 +66,11 @@ do_compat_cache_op(unsigned long start, unsigned long end, int flags)
 /*
  * Handle all unrecognised system calls.
  */
-long compat_arm_syscall(struct pt_regs *regs)
+long compat_arm_syscall(struct pt_regs *regs, int scno)
 {
-	unsigned int no = regs->regs[7];
 	void __user *addr;
 
-	switch (no) {
+	switch (scno) {
 	/*
 	 * Flush a region from virtual address 'r0' to virtual address 'r1'
 	 * _exclusive_.  There is no alignment requirement on either address;
@@ -107,7 +106,7 @@ long compat_arm_syscall(struct pt_regs *regs)
 		 * way the calling program can gracefully determine whether
 		 * a feature is supported.
 		 */
-		if (no < __ARM_NR_COMPAT_END)
+		if (scno < __ARM_NR_COMPAT_END)
 			return -ENOSYS;
 		break;
 	}
@@ -116,6 +115,6 @@ long compat_arm_syscall(struct pt_regs *regs)
 		(compat_thumb_mode(regs) ? 2 : 4);
 
 	arm64_notify_die("Oops - bad compat syscall(2)", regs,
-			 SIGILL, ILL_ILLTRP, addr, no);
+			 SIGILL, ILL_ILLTRP, addr, scno);
 	return 0;
 }

arch/arm64/kernel/syscall.c

@@ -13,16 +13,15 @@
 #include <asm/thread_info.h>
 #include <asm/unistd.h>
 
-long compat_arm_syscall(struct pt_regs *regs);
-
+long compat_arm_syscall(struct pt_regs *regs, int scno);
 long sys_ni_syscall(void);
 
-asmlinkage long do_ni_syscall(struct pt_regs *regs)
+static long do_ni_syscall(struct pt_regs *regs, int scno)
 {
 #ifdef CONFIG_COMPAT
 	long ret;
 	if (is_compat_task()) {
-		ret = compat_arm_syscall(regs);
+		ret = compat_arm_syscall(regs, scno);
 		if (ret != -ENOSYS)
 			return ret;
 	}
@@ -47,7 +46,7 @@ static void invoke_syscall(struct pt_regs *regs, unsigned int scno,
 		syscall_fn = syscall_table[array_index_nospec(scno, sc_nr)];
 		ret = __invoke_syscall(regs, syscall_fn);
 	} else {
-		ret = do_ni_syscall(regs);
+		ret = do_ni_syscall(regs, scno);
 	}
 
 	regs->regs[0] = ret;