Re: [PATCH v6 20/41] x86/mm: Teach pte_mkwrite() about stack memory

[Kees Cook]

On Sat, Feb 18, 2023 at 01:14:12PM -0800, Rick Edgecombe wrote:
> If a VMA has the VM_SHADOW_STACK flag, it is shadow stack memory. So
> when it is made writable with pte_mkwrite(), it should create shadow
> stack memory, not conventionally writable memory. Now that pte_mkwrite()
> takes a VMA, and places where shadow stack memory might be created pass
> one, pte_mkwrite() can know when it should do this.
> 
> So make pte_mkwrite() create shadow stack memory when the VMA has the
> VM_SHADOW_STACK flag. Do the same thing for pmd_mkwrite().
> 
> This requires referencing VM_SHADOW_STACK in these functions, which are
> currently defined in pgtable.h, however mm.h (where VM_SHADOW_STACK is
> located) can't be pulled in without causing problems for files that
> reference pgtable.h. So also move pte/pmd_mkwrite() into pgtable.c, where
> they can safely reference VM_SHADOW_STACK.
> 
> Tested-by: Pengfei Xu <pengfei.xu@xxxxxxxxx>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>

Is there any realistic performance impact from making these not inline
now?

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

-- 
Kees Cook