linux-kernel - [PATCH 10/11] Change mapping of kasan_zero

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Date:   Wed, 11 Oct 2017 16:22:26 +0800
From:   Abbott Liu <liuwenliang@...wei.com>
To:     <linux@...linux.org.uk>, <aryabinin@...tuozzo.com>,
        <liuwenliang@...wei.com>, <afzal.mohd.ma@...il.com>,
        <f.fainelli@...il.com>, <labbott@...hat.com>,
        <kirill.shutemov@...ux.intel.com>, <mhocko@...e.com>,
        <cdall@...aro.org>, <marc.zyngier@....com>,
        <catalin.marinas@....com>, <akpm@...ux-foundation.org>,
        <mawilcox@...rosoft.com>, <tglx@...utronix.de>,
        <thgarnie@...gle.com>, <keescook@...omium.org>, <arnd@...db.de>,
        <vladimir.murzin@....com>, <tixy@...aro.org>,
        <ard.biesheuvel@...aro.org>, <robin.murphy@....com>,
        <mingo@...nel.org>, <grygorii.strashko@...aro.org>
CC:     <glider@...gle.com>, <dvyukov@...gle.com>, <opendmb@...il.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <kasan-dev@...glegroups.com>,
        <linux-mm@...ck.org>, <jiazhenghua@...wei.com>,
        <dylix.dailei@...wei.com>, <zengweilin@...wei.com>,
        <heshaoliang@...wei.com>
Subject: [PATCH 10/11] Change mapping of kasan_zero_page int readonly

 Because the kasan_zero_page(which is used as the shadow
 region for some memory that KASan doesn't need to track.) won't be writen
 after kasan_init, so change the mapping of kasan_zero_page into readonly.

Cc: Andrey Ryabinin <a.ryabinin@...sung.com>
---
 arch/arm/mm/kasan_init.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/arm/mm/kasan_init.c b/arch/arm/mm/kasan_init.c
index 7cfdc39..c11826a 100644
--- a/arch/arm/mm/kasan_init.c
+++ b/arch/arm/mm/kasan_init.c
@@ -200,6 +200,7 @@ void __init kasan_init(void)
 {
 	struct memblock_region *reg;
 	u64 orig_ttbr0;
+	int i;
 
 	orig_ttbr0 = cpu_get_ttbr(0);
 
@@ -243,6 +244,17 @@ void __init kasan_init(void)
 	create_mapping((unsigned long)kasan_mem_to_shadow((void *)MODULES_VADDR),
 		(unsigned long)kasan_mem_to_shadow((void *)(PKMAP_BASE+PMD_SIZE)),
 		NUMA_NO_NODE);
+
+	/*
+	 * KAsan may reuse the contents of kasan_zero_pte directly, so we
+	 * should make sure that it maps the zero page read-only.
+	 */
+	for (i = 0; i < PTRS_PER_PTE; i++)
+                set_pte_at(&init_mm, KASAN_SHADOW_START + i*PAGE_SIZE,
+                        &kasan_zero_pte[i], pfn_pte(
+                                virt_to_pfn(kasan_zero_page),
+                                __pgprot(_L_PTE_DEFAULT | L_PTE_DIRTY | L_PTE_XN | L_PTE_RDONLY)));
+	memset(kasan_zero_page, 0, PAGE_SIZE);
 	cpu_set_ttbr0(orig_ttbr0);
 	flush_cache_all();
 	local_flush_bp_all();
-- 
2.9.0