Patch "arm64: Fix THP protection change logic" has been added to the 4.2-stable tree

This is a note to let you know that I've just added the patch titled

arm64: Fix THP protection change logic

to the 4.2-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
arm64-fix-thp-protection-change-logic.patch
and it can be found in the queue-4.2 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Steve Capper <[email protected]>
Date: Thu, 1 Oct 2015 13:06:07 +0100
Subject: arm64: Fix THP protection change logic

From: Steve Capper <[email protected]>

commit 1a541b4e3cd6f5795022514114854b3e1345f24e upstream.

6910fa1 ("arm64: enable PTE type bit in the mask for pte_modify") fixes a problem whereby a large block of PROT_NONE mapped memory is incorrectly mapped as block descriptors when mprotect is called.

Unfortunately, a subtle bug was introduced by this fix to the THP logic.

If one mmaps a large block of memory, then faults it such that it is collapsed into THPs; resulting calls to mprotect on this area of memory will lead to incorrect table descriptors being written instead of block descriptors. This is because pmd_modify calls pte_modify which is now allowed to modify the type of the page table entry.

This patch reverts commit 6910fa16dbe142f6a0fd0fd7c249f9883ff7fc8a, and fixes the problem it was trying to address by adjusting PAGE_NONE to represent a table entry. Thus no change in pte type is required when moving from PROT_NONE to a different protection.

[SteveC: backported 1a541b4e3cd6f5795022514114854b3e1345f24e to 4.1 and
4.2 stable. Just one minor fix to second part to allow patch to apply
cleanly, no logic changed.]

---
 arch/arm64/include/asm/pgtable.h |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

@@ -80,7 +80,7 @@ extern void __pgd_error(const char *file
 #define PAGE_S2			__pgprot(PROT_DEFAULT | PTE_S2_MEMATTR(MT_S2_NORMAL) | PTE_S2_RDONLY)
 #define PAGE_S2_DEVICE		__pgprot(PROT_DEFAULT | PTE_S2_MEMATTR(MT_S2_DEVICE_nGnRE) | PTE_S2_RDONLY | PTE_UXN)
 
-#define PAGE_NONE		__pgprot(((_PAGE_DEFAULT) & ~PTE_TYPE_MASK) | PTE_PROT_NONE | PTE_PXN | PTE_UXN)
+#define PAGE_NONE		__pgprot(((_PAGE_DEFAULT) & ~PTE_VALID) | PTE_PROT_NONE | PTE_PXN | PTE_UXN)
 #define PAGE_SHARED		__pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_UXN | PTE_WRITE)
 #define PAGE_SHARED_EXEC	__pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_WRITE)
 #define PAGE_COPY		__pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_UXN)

@@ -460,7 +460,7 @@ static inline pud_t *pud_offset(pgd_t *p
 static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
 {
 	const pteval_t mask = PTE_USER | PTE_PXN | PTE_UXN | PTE_RDONLY |
-			      PTE_PROT_NONE | PTE_WRITE | PTE_TYPE_MASK;
+			      PTE_PROT_NONE | PTE_VALID | PTE_WRITE;
 	pte_val(pte) = (pte_val(pte) & ~mask) | (pgprot_val(newprot) & mask);
 	return pte;
 }

Patches currently in stable-queue which might be from [email protected] are

queue-4.2/arm64-fix-thp-protection-change-logic.patch