From: Steven Rostedt <srostedt@redhat.com>
Date: Thu, 19 Feb 2009 16:46:36 +0000 (-0500)
Subject: x86: check PMD in spurious_fault handler
X-Git-Tag: v2.6.30-rc1~211^2~43^5~15^2
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=3c3e5694add02e665bbbd0fecfbbdcc0b903097a;p=karo-tx-linux.git

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 c76ef1d701c9..278d645d108a 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_ONCE(!ret, "PMD has incorrect permission bits\n");
+	return ret;
 }
 
 /*