Re: [PATCH v4 23/39] mm: Don't allow write GUPs to shadow stack memory

[Kees Cook]

On Fri, Dec 02, 2022 at 04:35:50PM -0800, Rick Edgecombe wrote:
> The x86 Control-flow Enforcement Technology (CET) feature includes a new
> type of memory called shadow stack. This shadow stack memory has some
> unusual properties, which requires some core mm changes to function
> properly.
> 
> Shadow stack memory is writable only in very specific, controlled ways.
> However, since it is writable, the kernel treats it as such. As a result
> there remain many ways for userspace to trigger the kernel to write to
> shadow stack's via get_user_pages(, FOLL_WRITE) operations. To make this a
> little less exposed, block writable GUPs for shadow stack VMAs.
> 
> Still allow FOLL_FORCE to write through shadow stack protections, as it
> does for read-only protections.
> 
> Tested-by: Pengfei Xu <pengfei.xu@xxxxxxxxx>
> Tested-by: John Allen <john.allen@xxxxxxx>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

-- 
Kees Cook