[PATCH 1/6] x86: check PMD in spurious_fault handler

[Steven Rostedt <rostedt@goodmis.org>]

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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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