Re: [PATCH v26 24/30] x86/cet/shstk: Introduce shadow stack token setup/verify routines

Yu, Yu-cheng
2021-05-18T18:05:38Z

On 5/17/2021 5:14 PM, Eugene Syromiatnikov wrote:
> On Mon, May 17, 2021 at 01:55:01PM -0700, Yu, Yu-cheng wrote:
>> On 5/17/2021 12:45 AM, Borislav Petkov wrote:
>>> On Tue, Apr 27, 2021 at 01:43:09PM -0700, Yu-cheng Yu wrote:
>>>> +static inline int write_user_shstk_32(u32 __user *addr, u32 val)
>>>> +{
>>>> + WARN_ONCE(1, "%s used but not supported.\n", __func__);
>>>> + return -EFAULT;
>>>> +}
>>>> +#endif
>>>
>>> What is that supposed to catch? Any concrete (mis-)use cases?
>>>
>>
>> If 32-bit apps are not supported, there should be no need of 32-bit shadow
>> stack write, otherwise there is a bug.
>
> Speaking of which, I wonder what would happen if a 64-bit process makes
> a 32-bit system call (using int 0x80, for example), and gets a signal.
>

Yes, that's right. Thanks! I should have said, if neither IA32 nor X32
is supported.

Yu-cheng