Re: [PATCH v2 3/3] audit: Use syscall_get_return_value to get syscall return code in audit_syscall_exit

[He Zhe]

On 5/11/21 6:38 AM, Paul Moore wrote:
> On Fri, Apr 23, 2021 at 6:36 AM He Zhe <zhe.he@xxxxxxxxxxxxx> wrote:
>> regs_return_value for some architectures like arm64 simply retrieve
>> register value from pt_regs without sign extension in 32-bit compatible
>> case and cause audit to have false syscall return code. For example,
>> 32-bit -13 would be treated as 4294967283 below.
>>
>> type=SYSCALL msg=audit(1611110715.887:582): arch=40000028 syscall=322
>> success=yes exit=4294967283
>>
>> We just added proper sign extension in syscall_get_return_value which
>> should be used instead.
>>
>> Signed-off-by: He Zhe <zhe.he@xxxxxxxxxxxxx>
>> ---
>> v1 to v2: No change
>>
>>  include/linux/audit.h | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
> Perhaps I missed it but did you address the compile error that was
> found by the kernel test robot?

I sent a patch adding syscall_get_return_value for alpha to fix this bot warning.
https://lore.kernel.org/lkml/20210426091629.45020-1-zhe.he@xxxxxxxxxxxxx/
which can be found in this mail thread.

>
> Regardless, one comment inline below ...
>
>> diff --git a/include/linux/audit.h b/include/linux/audit.h
>> index 82b7c1116a85..135adbe22c19 100644
>> --- a/include/linux/audit.h
>> +++ b/include/linux/audit.h
>> @@ -334,7 +334,7 @@ static inline void audit_syscall_exit(void *pt_regs)
>>  {
>>         if (unlikely(audit_context())) {
>>                 int success = is_syscall_success(pt_regs);
> Since we are shifting to use syscall_get_return_value() below, would
> it also make sense to shift to using syscall_get_error() here instead
> of is_syscall_success()?

In [PATCH v2 1/3], is_syscall_success calls syscall_get_return_value to take
care of the sign extension issue. Keeping using is_syscall_success is to not
potentially changing other architectures' behavior.

Thanks,
Zhe

>
>> -               long return_code = regs_return_value(pt_regs);
>> +               long return_code = syscall_get_return_value(current, pt_regs);
>>
>>                 __audit_syscall_exit(success, return_code);
>>         }