Re: [PATCH v2 2/3] proc: query LSMs for introspective mem access (if PROC_MEM_FORCE_ALWAYS)

["David Hildenbrand (Arm)" <david@kernel.org>]

On 8/25/26 20:39, Jann Horn wrote:
> If the system is running with PROC_MEM_FORCE_ALWAYS, LSMs currently have no
> good opportunity to block a process from overwriting read-only code in its
> own address space through FOLL_FORCE writes via /proc/self/mem.
> The security_ptrace_access_check() LSM hook is bypassed when a process
> opens /proc/self/mem because this is considered "introspection".
> 
> This causes a hole in SELinux EXECMEM enforcement, which tries to ensure
> that a process cannot create executable anonymous pages.
> 
> PROC_MEM_FORCE_PTRACE prevents that and ensures that such FOLL_FORCE
> accesses are only possible when the LSM allows ptrace() attachment; but it
> is unclear how quickly PROC_MEM_FORCE_PTRACE can be deployed in
> environments running lots of third-party code, such as Android.
> 
> So, introduce a new LSM hook that can forbid FOLL_FORCE specifically for
> such "introspective" accesses.
> 
> Signed-off-by: Jann Horn <jannh@google.com>
> ---

Acked-by: David Hildenbrand (Arm) <david@kernel.org>

-- 
Cheers,

David