• Michael Neuling's avatar
    powerpc: Avoid code patching freed init sections · 51c3c62b
    Michael Neuling authored
    This stops us from doing code patching in init sections after they've
    been freed.
    
    In this chain:
      kvm_guest_init() ->
        kvm_use_magic_page() ->
          fault_in_pages_readable() ->
    	 __get_user() ->
    	   __get_user_nocheck() ->
    	     barrier_nospec();
    
    We have a code patching location at barrier_nospec() and
    kvm_guest_init() is an init function. This whole chain gets inlined,
    so when we free the init section (hence kvm_guest_init()), this code
    goes away and hence should no longer be patched.
    
    We seen this as userspace memory corruption when using a memory
    checker while doing partition migration testing on powervm (this
    starts the code patching post migration via
    /sys/kernel/mobility/migration). In theory, it could also happen when
    using /sys/kernel/debug/powerpc/barrier_nospec.
    
    Cc: stable@vger.kernel.org # 4.13+
    Signed-off-by: default avatarMichael Neuling <mikey@neuling.org>
    Reviewed-by: default avatarNicholas Piggin <npiggin@gmail.com>
    Reviewed-by: default avatarChristophe Leroy <christophe.leroy@c-s.fr>
    Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
    51c3c62b
mem.c 15.3 KB