Patch "arm64: mm: fix thinko in non-global page table attribute check" has been added to the 4.14-stable tree

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

arm64: mm: fix thinko in non-global page table attribute check

to the 4.14-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-mm-fix-thinko-in-non-global-page-table-attribute-check.patch
and it can be found in the queue-4.14 subdirectory.

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

From: Ard Biesheuvel <[email protected]>
Date: Fri, 23 Feb 2018 18:04:48 +0000
Subject: arm64: mm: fix thinko in non-global page table attribute check

From: Ard Biesheuvel <[email protected]>

commit 753e8abc36b2c966caea075db0c845563c8a19bf upstream.

The routine pgattr_change_is_safe() was extended in commit 4e6020565596 ("arm64: mm: Permit transitioning from Global to Non-Global without BBM") to permit changing the nG attribute from not set to set, but did so in a way that inadvertently disallows such changes if other permitted attribute changes take place at the same time. So update the code to take this into account.

---
 arch/arm64/mm/mmu.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

@@ -107,7 +107,7 @@ static bool pgattr_change_is_safe(u64 ol
 	 * The following mapping attributes may be updated in live
 	 * kernel mappings without the need for break-before-make.
 	 */
-	static const pteval_t mask = PTE_PXN | PTE_RDONLY | PTE_WRITE;
+	static const pteval_t mask = PTE_PXN | PTE_RDONLY | PTE_WRITE | PTE_NG;
 
 	/* creating or taking down mappings is always safe */
 	if (old == 0 || new == 0)

@@ -117,9 +117,9 @@ static bool pgattr_change_is_safe(u64 ol
 	if ((old | new) & PTE_CONT)
 		return false;
 
-	/* Transitioning from Global to Non-Global is safe */
-	if (((old ^ new) == PTE_NG) && (new & PTE_NG))
-		return true;
+	/* Transitioning from Non-Global to Global is unsafe */
+	if (old & ~new & PTE_NG)
+		return false;
 
 	return ((old ^ new) & ~mask) == 0;
 }

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

queue-4.14/arm64-mm-fix-thinko-in-non-global-page-table-attribute-check.patch