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[PATCH 2/2] x86/kasan: write protect kasan zero shadow

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After kasan_init() executed, no one is allowed to write to kasan_zero_page,
so write protect it.

Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
---
 arch/x86/mm/kasan_init_64.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/kasan_init_64.c b/arch/x86/mm/kasan_init_64.c
index 303e470..1b1110f 100644
--- a/arch/x86/mm/kasan_init_64.c
+++ b/arch/x86/mm/kasan_init_64.c
@@ -125,10 +125,16 @@ void __init kasan_init(void)
 
 	/*
 	 * kasan_zero_page has been used as early shadow memory, thus it may
-	 * contain some garbage. Now we can clear it, since after the TLB flush
-	 * no one should write to it.
+	 * contain some garbage. Now we can clear and write protect it, since
+	 * after the TLB flush no one should write to it.
 	 */
 	memset(kasan_zero_page, 0, PAGE_SIZE);
+	for (i = 0; i < PTRS_PER_PTE; i++) {
+		pte_t pte = __pte(__pa(kasan_zero_page) | __PAGE_KERNEL_RO);
+		set_pte(&kasan_zero_pte[i], pte);
+	}
+	/* Flush TLBs again to be sure that write protection applied. */
+	__flush_tlb_all();
 
 	init_task.kasan_depth = 0;
 	pr_info("KernelAddressSanitizer initialized\n");
-- 
2.4.10

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[RFC 01/13] x86/paravirt: Turn KASAN off for parvirt.o Andy Lutomirski <luto@kernel.org> - 2016-01-09 00:20 +0100
  Re: [RFC 01/13] x86/paravirt: Turn KASAN off for parvirt.o Borislav Petkov <bp@alien8.de> - 2016-01-10 20:10 +0100
    [PATCH 2/2] x86/kasan: write protect kasan zero shadow Andrey Ryabinin <aryabinin@virtuozzo.com> - 2016-01-11 14:00 +0100
    Re: [RFC 01/13] x86/paravirt: Turn KASAN off for parvirt.o Andrey Ryabinin <aryabinin@virtuozzo.com> - 2016-01-11 14:00 +0100
      [PATCH 1/2] x86/kasan: clear kasan_zero_page after TLB flush Andrey Ryabinin <aryabinin@virtuozzo.com> - 2016-01-11 14:00 +0100

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