[PATCH v7 13/23] aarch64: Enable GCS in dynamic linked exe

[Adhemerval Zanella Netto]

On 08/01/25 10:52, Yury Khrustalev wrote:
> On Tue, Jan 07, 2025 at 01:50:41PM -0300, Adhemerval Zanella Netto wrote:
>>
>>> +	/* Enable GCS before user code runs.  Note that IFUNC resolvers and
>>> +	   LD_AUDIT hooks may run before, but should not create threads.  */
>>> +#define PR_SET_SHADOW_STACK_STATUS  75
>>> +#define PR_SHADOW_STACK_ENABLE      (1UL << 0)
>>> +	mov	x0, PR_SET_SHADOW_STACK_STATUS
>>> +	mov	x1, PR_SHADOW_STACK_ENABLE
>>> +	mov	x2, 0
>>> +	mov	x3, 0
>>> +	mov	x4, 0
>>> +	mov	x8, #SYS_ify(prctl)
>>> +	svc	0x0
>>
>> Should it handle errors, for the case prctl is filtered or blocked?
> 
> There is no need to handle errors here. If this syscall doesn't succeed, it
> would be the same as if we didn't make it at all: GCS will remain disabled.
> 
> Having a check for error here would be an unnecessary overhead.

But this is aaik not how other security hardening work, like BTI where 
_dl_bti_check will _dl_fatal_printf if bti can not be enabled.  Without a 
check, GCS is taking as a hint, not as enforcement