Re: [PATCH v11 25/25] x86/cet/shstk: Add arch_prctl functions for shadow stack

Florian Weimer
2020-08-26T16:52:38Z

* Dave Martin:

> On Tue, Aug 25, 2020 at 04:34:27PM -0700, Yu, Yu-cheng wrote:
>> On 8/25/2020 4:20 PM, Dave Hansen wrote:
>> >On 8/25/20 2:04 PM, Yu, Yu-cheng wrote:
>> >>>>I think this is more arch-specific.  Even if it becomes a new syscall,
>> >>>>we still need to pass the same parameters.
>> >>>
>> >>>Right, but without the copying in and out of memory.
>> >>>
>> >>Linux-api is already on the Cc list.  Do we need to add more people to
>> >>get some agreements for the syscall?
>> >What kind of agreement are you looking for? I'd suggest just coding it
>> >up and posting the patches. Adding syscalls really is really pretty
>> >straightforward and isn't much code at all.
>> >
>>
>> Sure, I will do that.
>
> Alternatively, would a regular prctl() work here?

Is this something appliation code has to call, or just the dynamic
loader?

prctl in glibc is a variadic function, so if there's a mismatch between
the kernel/userspace syscall convention and the userspace calling
convention (for variadic functions) for specific types, it can't be made
to work in a generic way.

The loader can use inline assembly for system calls and does not have
this issue, but applications would be implcated by it.

Thanks,
Florian