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    Subject[tip:x86/mm] x86/mm/64: In vmalloc_fault(), use CR3 instead of current->active_mm
    Commit-ID:  46aea3873401836abb7f01200e7946e7d518b359
    Gitweb: http://git.kernel.org/tip/46aea3873401836abb7f01200e7946e7d518b359
    Author: Andy Lutomirski <luto@kernel.org>
    AuthorDate: Thu, 14 Jul 2016 13:22:54 -0700
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitDate: Fri, 15 Jul 2016 10:26:27 +0200

    x86/mm/64: In vmalloc_fault(), use CR3 instead of current->active_mm

    If we get a vmalloc fault while current->active_mm->pgd doesn't
    match CR3, we'll crash without this change. I've seen this failure
    mode on heavily instrumented kernels with virtually mapped stacks.

    Signed-off-by: Andy Lutomirski <luto@kernel.org>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Brian Gerst <brgerst@gmail.com>
    Cc: Denys Vlasenko <dvlasenk@redhat.com>
    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Josh Poimboeuf <jpoimboe@redhat.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Link: http://lkml.kernel.org/r/4650d7674185f165ed8fdf9ac4c5c35c5c179ba8.1468527351.git.luto@kernel.org
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    arch/x86/mm/fault.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
    index 7d1fa7c..ca44e2e 100644
    --- a/arch/x86/mm/fault.c
    +++ b/arch/x86/mm/fault.c
    @@ -439,7 +439,7 @@ static noinline int vmalloc_fault(unsigned long address)
    * happen within a race in page table update. In the later
    * case just flush:
    */
    - pgd = pgd_offset(current->active_mm, address);
    + pgd = (pgd_t *)__va(read_cr3()) + pgd_index(address);
    pgd_ref = pgd_offset_k(address);
    if (pgd_none(*pgd_ref))
    return -1;
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