Commit 753e8abc authored Feb 23, 2018 by Ard Biesheuvel Committed by Catalin Marinas Feb 26, 2018

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



The routine pgattr_change_is_safe() was extended in commit 4e602056
("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.

Fixes: 4e602056 ("arm64: mm: Permit transitioning from Global to ...")
Cc: <stable@vger.kernel.org> # 4.14.x-
Acked-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

parent 4a3928c6

arch/arm64/mm/mmu.c

+4 −4

Original line number	Diff line number	Diff line
		@@ -108,7 +108,7 @@ static bool pgattr_change_is_safe(u64 old, u64 new)
		* 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)
		@@ -118,9 +118,9 @@ static bool pgattr_change_is_safe(u64 old, u64 new)
		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;
		}

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