proc: query LSMs for introspective mem access (if PROC_MEM_FORCE_ALWAYS)

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>
Link: https://patch.msgid.link/20260907-selinux-pokemem-v3-2-0bafbaeafe50@google.com
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

0 files changed, 0 insertions, 0 deletions