• Nadav Amit's avatar
    x86/mm: Use WRITE_ONCE() when setting PTEs · 9bc4f28a
    Nadav Amit authored
    When page-table entries are set, the compiler might optimize their
    assignment by using multiple instructions to set the PTE. This might
    turn into a security hazard if the user somehow manages to use the
    interim PTE. L1TF does not make our lives easier, making even an interim
    non-present PTE a security hazard.
    
    Using WRITE_ONCE() to set PTEs and friends should prevent this potential
    security hazard.
    
    I skimmed the differences in the binary with and without this patch. The
    differences are (obviously) greater when CONFIG_PARAVIRT=n as more
    code optimizations are possible. For better and worse, the impact on the
    binary with this patch is pretty small. Skimming the code did not cause
    anything to jump out as a security hazard, but it seems that at least
    move_soft_dirty_pte() caused set_pte_at() to use multiple writes.
    Signed-off-by: default avatarNadav Amit <namit@vmware.com>
    Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
    Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
    Cc: Dave Hansen <dave.hansen@linux.intel.com>
    Cc: Andi Kleen <ak@linux.intel.com>
    Cc: Josh Poimboeuf <jpoimboe@redhat.com>
    Cc: Michal Hocko <mhocko@suse.com>
    Cc: Vlastimil Babka <vbabka@suse.cz>
    Cc: Sean Christopherson <sean.j.christopherson@intel.com>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: stable@vger.kernel.org
    Link: https://lkml.kernel.org/r/20180902181451.80520-1-namit@vmware.com
    9bc4f28a
pgtable_64.h 7.26 KB