2010-07-27 08:06:32

by Shaohua Li

Subject: [PATCH]x86: make spurious_fault check correct pte bit

pte_present() returns true even present bit isn't set but _PAGE_PROTNONE
(global bit) bit is set. While with CONFIG_DEBUG_PAGEALLOC, free pages have
global bit set but present bit clear. This patch makes we could catch
free pages access with CONFIG_DEBUG_PAGEALLOC enabled.

Signed-off-by: Shaohua Li <[email protected]>

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index f627779..93afd78 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -893,7 +893,7 @@ spurious_fault(unsigned long error_code, unsigned long address)
return spurious_fault_check(error_code, (pte_t *) pmd);

pte = pte_offset_kernel(pmd, address);
- if (!pte_present(*pte))
+ if (!(pte_flags(*pte) & _PAGE_PRESENT))
return 0;

ret = spurious_fault_check(error_code, pte);

2010-08-26 23:13:31

by Shaohua Li

Subject: [tip:x86/mm] x86, mm: Make spurious_fault check explicitly check the PRESENT bit

Commit-ID: 660a293ea9be709b893d371fbc0328fcca33c33a
Gitweb: http://git.kernel.org/tip/660a293ea9be709b893d371fbc0328fcca33c33a
Author: Shaohua Li <[email protected]>
AuthorDate: Tue, 27 Jul 2010 16:06:28 +0800
Committer: H. Peter Anvin <[email protected]>
CommitDate: Thu, 26 Aug 2010 16:00:21 -0700

x86, mm: Make spurious_fault check explicitly check the PRESENT bit

pte_present() returns true even present bit isn't set but _PAGE_PROTNONE
(global bit) bit is set. While with CONFIG_DEBUG_PAGEALLOC, free pages have
global bit set but present bit clear. This patch makes we could catch
free pages access with CONFIG_DEBUG_PAGEALLOC enabled.

[ hpa: added a comment in the code as a warning to janitors ]

Signed-off-by: Shaohua Li <[email protected]>
LKML-Reference: <[email protected]>
Signed-off-by: H. Peter Anvin <[email protected]>
---
arch/x86/mm/fault.c | 8 +++++++-
1 files changed, 7 insertions(+), 1 deletions(-)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 51f7ee7..caec229 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -872,8 +872,14 @@ spurious_fault(unsigned long error_code, unsigned long address)
if (pmd_large(*pmd))
return spurious_fault_check(error_code, (pte_t *) pmd);

+ /*
+ * Note: don't use pte_present() here, since it returns true
+ * if the _PAGE_PROTNONE bit is set. However, this aliases the
+ * _PAGE_GLOBAL bit, which for kernel pages give false positives
+ * when CONFIG_DEBUG_PAGEALLOC is used.
+ */
pte = pte_offset_kernel(pmd, address);
- if (!pte_present(*pte))
+ if (!(pte_flags(*pte) & _PAGE_PRESENT))
return 0;

ret = spurious_fault_check(error_code, pte);