Re: [PATCH v2 22/39] mm: Don't allow write GUPs to shadow stack memory

From: Andy Lutomirski
Date: Mon Oct 03 2022 - 18:49:36 EST

On 10/3/22 11:39, Kees Cook wrote:
On Thu, Sep 29, 2022 at 03:29:19PM -0700, Rick Edgecombe wrote:
Still allow FOLL_FORCE to write through shadow stack protections, as it
does for read-only protections.

As I asked in the cover letter: why do we need to add this for shstk? It
was a mistake for general memory. :P

For debuggers, which use FOLL_FORCE, quite intentionally, to modify text. And once a debugger has ptrace write access to a target, shadow stacks provide exactly no protection -- ptrace can modify text and all registers.

But /proc/.../mem may be a different story, and I'd be okay with having FOLL_PROC_MEM for legacy compatibility via /proc/.../mem and not allowing that to access shadow stacks. This does seem like it may not be very useful, though.