Re: [PATCH] arm64: audit: fix return value high 32bit truncation problem

From: weiyuchen <redacted>

Add error code judgment in invoke_syscall() to prevent kernel
components such as audit and tracepoint from obtaining incorrect
return values. For example:

type=SYSCALL msg=audit(342.780:69): arch=40000028 syscall=235
success=yes exit=4294967235

The syscall return value is -61, but due to the following process in
invoke_syscall():

	if (is_compat_task())
		ret = lower_32_bits(ret);
	regs->regs[0] = ret;

The return value audit or tracepoint get from regs[0] is 4294967235,
which is an incorrect return value.

Signed-off-by: weiyuchen <redacted>
---
 arch/arm64/kernel/syscall.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c
index 263d6c1a525f..f9f042d9a088 100644
--- a/arch/arm64/kernel/syscall.c
+++ b/arch/arm64/kernel/syscall.c

@@ -54,7 +54,7 @@ static void invoke_syscall(struct pt_regs *regs, unsigned int scno,
 		ret = do_ni_syscall(regs, scno);
 	}
 
-	if (is_compat_task())
+	if (is_compat_task() && !IS_ERR_VALUE(ret))
 		ret = lower_32_bits(ret);