• Andrey Ryabinin's avatar
    x86/kasan: Fix boot with 5-level paging and KASAN · 3fd63c38
    Andrey Ryabinin authored
    commit f3176ec9 upstream.
    
    Since commit d52888aa ("x86/mm: Move LDT remap out of KASLR region on
    5-level paging") kernel doesn't boot with KASAN on 5-level paging machines.
    The bug is actually in early_p4d_offset() and introduced by commit
    12a8cc7f ("x86/kasan: Use the same shadow offset for 4- and 5-level paging")
    
    early_p4d_offset() tries to convert pgd_val(*pgd) value to a physical
    address. This doesn't make sense because pgd_val() already contains the
    physical address.
    
    It did work prior to commit d52888aa because the result of
    "__pa_nodebug(pgd_val(*pgd)) & PTE_PFN_MASK" was the same as "pgd_val(*pgd)
    & PTE_PFN_MASK". __pa_nodebug() just set some high bits which were masked
    out by applying PTE_PFN_MASK.
    
    After the change of the PAGE_OFFSET offset in commit d52888aa
    __pa_nodebug(pgd_val(*pgd)) started to return a value with more high bits
    set and PTE_PFN_MASK wasn't enough to mask out all of them. So it returns a
    wrong not even canonical address and crashes on the attempt to dereference
    it.
    
    Switch back to pgd_val() & PTE_PFN_MASK to cure the issue.
    
    Fixes: 12a8cc7f ("x86/kasan: Use the same shadow offset for 4- and 5-level paging")
    Reported-by: default avatarKirill A. Shutemov <kirill@shutemov.name>
    Signed-off-by: default avatarAndrey Ryabinin <aryabinin@virtuozzo.com>
    Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: "H. Peter Anvin" <hpa@zytor.com>
    Cc: Alexander Potapenko <glider@google.com>
    Cc: Dmitry Vyukov <dvyukov@google.com>
    Cc: kasan-dev@googlegroups.com
    Cc: stable@vger.kernel.org
    Cc: <stable@vger.kernel.org>
    Link: https://lkml.kernel.org/r/20190614143149.2227-1-aryabinin@virtuozzo.comSigned-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    3fd63c38
kasan_init_64.c 10.2 KB