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arm64: kasan: ensure that the KASAN zero page is mapped read-only

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When switching from the early KASAN shadow region, which maps the
entire shadow space read-write, to the permanent KASAN shadow region,
which uses a zero page to shadow regions that are not subject to
instrumentation, the lowest level table kasan_zero_pte[] may be
reused unmodified, which means that the mappings of the zero page
that it contains will still be read-write.

So update it explicitly to map the zero page read only when we
activate the permanent mapping.

Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
Ard Biesheuvel 2016-01-11 14:50:21 +01:00 committed by Will Deacon
parent 75feee3d9d
commit 7b1af97957
1 changed files with 9 additions and 0 deletions
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9
arch/arm64/mm/kasan_init.c
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@ -120,6 +120,7 @@ static void __init cpu_set_ttbr1(unsigned long ttbr1)
void __init kasan_init(void)
{
struct memblock_region *reg;
int i;
/*
* We are going to perform proper setup of shadow memory.
@ -155,6 +156,14 @@ void __init kasan_init(void)
pfn_to_nid(virt_to_pfn(start)));
}
/*
* 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(&kasan_zero_pte[i],
pfn_pte(virt_to_pfn(kasan_zero_page), PAGE_KERNEL_RO));
memset(kasan_zero_page, 0, PAGE_SIZE);
cpu_set_ttbr1(__pa(swapper_pg_dir));
flush_tlb_all();