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    Subject[PATCH 1/6] x86: check PMD in spurious_fault handler
    From: Steven Rostedt <srostedt@redhat.com>

    Impact: fix to prevent hard lockup on bad PMD permissions

    If the PMD does not have the correct permissions for a page access,
    but the PTE does, the spurious fault handler will mistake the fault
    as a lazy TLB transaction. This will result in an infinite loop of:

    fault -> spurious_fault check (pass) -> return to code -> fault

    This patch adds a check and a warn on if the PTE passes the permissions
    but the PMD does not.

    Signed-off-by: Steven Rostedt <srostedt@redhat.com>
    ---
    arch/x86/mm/fault.c | 13 ++++++++++++-
    1 files changed, 12 insertions(+), 1 deletions(-)

    diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
    index c76ef1d..7b579a6 100644
    --- a/arch/x86/mm/fault.c
    +++ b/arch/x86/mm/fault.c
    @@ -455,6 +455,7 @@ static int spurious_fault(unsigned long address,
    pud_t *pud;
    pmd_t *pmd;
    pte_t *pte;
    + int ret;

    /* Reserved-bit violation or user access to kernel space? */
    if (error_code & (PF_USER | PF_RSVD))
    @@ -482,7 +483,17 @@ static int spurious_fault(unsigned long address,
    if (!pte_present(*pte))
    return 0;

    - return spurious_fault_check(error_code, pte);
    + ret = spurious_fault_check(error_code, pte);
    + if (!ret)
    + return 0;
    +
    + /*
    + * Make sure we have permissions in PMD
    + * If not, then there's a bug in the page tables.
    + */
    + ret = spurious_fault_check(error_code, (pte_t *) pmd);
    + WARN_ON(!ret);
    + return ret;
    }

    /*
    --
    1.5.6.5
    --


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