linux-kernel - [PATCH 1/2] arm64: Get existing page protections in split

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Date:	Tue,  3 Nov 2015 13:48:34 -0800
From:	Laura Abbott <labbott@...oraproject.org>
To:	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>
Cc:	Laura Abbott <labbott@...oraproject.org>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Kees Cook <keescook@...omium.org>,
	Xishi Qiu <qiuxishi@...wei.com>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Mark Rutland <mark.rutland@....com>
Subject: [PATCH 1/2] arm64: Get existing page protections in split_pmd


Rather than always putting the least restrictived permissions
(PAGE_KERNEL_EXEC) when spliting a pmd into pages, use
the existing permissions from the pmd for the page.

Signed-off-by: Laura Abbott <labbott@...oraproject.org>
---
 arch/arm64/mm/mmu.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 9211b85..ff41efa 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -75,14 +75,13 @@ static void __init *early_alloc(unsigned long sz)
 static void split_pmd(pmd_t *pmd, pte_t *pte)
 {
 	unsigned long pfn = pmd_pfn(*pmd);
+	unsigned long addr = pfn << PAGE_SHIFT;
+	pgprot_t prot = __pgprot(pmd_val(*pmd) ^ addr) | PTE_TYPE_PAGE;
+
 	int i = 0;
 
 	do {
-		/*
-		 * Need to have the least restrictive permissions available
-		 * permissions will be fixed up later
-		 */
-		set_pte(pte, pfn_pte(pfn, PAGE_KERNEL_EXEC));
+		set_pte(pte, pfn_pte(pfn, prot));
 		pfn++;
 	} while (pte++, i++, i < PTRS_PER_PTE);
 }
-- 
2.4.3

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