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

From: Dave Hansen
Date: Tue Sep 08 2020 - 13:57:43 EST

On 9/8/20 10:50 AM, Yu, Yu-cheng wrote:
> What about this:
> - Do not add any new syscall or arch_prctl for creating a new shadow stack.
> - Add a new arch_prctl that can turn an anonymous mapping to a shadow
> stack mapping.
> This allows the application to do whatever is necessary.  It can even
> allow GDB or JIT code to create or fix a call stack.

Fine with me. But, it's going to effectively be

arch_prctl(PR_CONVERT_TO_SHS..., addr, len);

when it could just as easily be:

madvise(addr, len, MADV_SHSTK...);

Or a new syscall. The only question in my mind is whether we want to do
something generic that we can use for other similar things in the
future, like:

madvise2(addr, len, flags, MADV2_SHSTK...);

I don't really feel strongly about it, though. Could you please share
your logic on why you want a prctl() as opposed to a whole new syscall?