Messages in this thread | | | Date | Mon, 3 Oct 2022 15:49:18 -0700 | Subject | Re: [PATCH v2 22/39] mm: Don't allow write GUPs to shadow stack memory | From | Andy Lutomirski <> |
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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.
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