Re: [PATCH v3 2/3] proc: query LSMs for introspective mem access (if PROC_MEM_FORCE_ALWAYS)

[sashiko-bot@kernel.org]

> 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.
> 
> Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
> Acked-by: David Hildenbrand (Arm) <david@kernel.org>
> Signed-off-by: Jann Horn <jannh@google.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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