Re: [PATCH v19 24/25] x86/cet/shstk: Add arch_prctl functions for shadow stack

On Thu, Feb 04, 2021 at 03:41:59PM -0800, Yu, Yu-cheng wrote:

On 2/4/2021 12:35 PM, Kees Cook wrote:

quoted

On Wed, Feb 03, 2021 at 02:55:46PM -0800, Yu-cheng Yu wrote:

quoted

arch_prctl(ARCH_X86_CET_STATUS, u64 *args)
     Get CET feature status.

     The parameter 'args' is a pointer to a user buffer.  The kernel returns
     the following information:

     *args = shadow stack/IBT status
     *(args + 1) = shadow stack base address
     *(args + 2) = shadow stack size

What happens if this needs to grow in the future? Should the first u64
contain the array size?

Otherwise, looks sensible.

-Kees

The first item is a bitmap, and there are two possible bits.  Should there
be a need, we can then do things about it.  My thought at the moment is, we
may not meet the situation.  Can we keep this for now?

Ah, good point. Yes, since that's a bitmap it ends up describing what
follows. This is fine as-is. Thanks!

Reviewed-by: Kees Cook <redacted>


-- 
Kees Cook