x86: check PMD in spurious_fault handler
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.
[ Updated: Ingo Molnar suggested using WARN_ONCE with some text ]
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index c76ef1d..278d645 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -455,6 +455,7 @@
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 @@
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_ONCE(!ret, "PMD has incorrect permission bits\n");
+ return ret;
}
/*