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SubjectRe: [PATCH] arm64: audit: fix return value high 32bit truncation problem
On Thu, Jul 22, 2021 at 02:07:07PM +0800, Yuchen Wei wrote:
> From: weiyuchen <weiyuchen3@huawei.com>
>
> 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 <weiyuchen3@huawei.com>
> ---
> 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);

Hmm, I'm worried this might break other users who don't expect to see
non-zero bits for the upper 32-bits of a compat task.

Mark -- I remember you looking into this relatively recently. Where did you
get to with it?

Will

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