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authorArd Biesheuvel <ard.biesheuvel@linaro.org>2016-01-26 16:12:01 +0300
committerCatalin Marinas <catalin.marinas@arm.com>2016-02-24 17:57:27 +0300
commitf80fb3a3d50843a401dac4b566b3b131da8077a2 (patch)
tree1861584ef7bbae384b12bfc70dc5974328995506 /arch/arm64/mm/kasan_init.c
parent1e48ef7fcc374051730381a2a05da77eb4eafdb0 (diff)
downloadlinux-f80fb3a3d50843a401dac4b566b3b131da8077a2.tar.xz
arm64: add support for kernel ASLR
This adds support for KASLR is implemented, based on entropy provided by the bootloader in the /chosen/kaslr-seed DT property. Depending on the size of the address space (VA_BITS) and the page size, the entropy in the virtual displacement is up to 13 bits (16k/2 levels) and up to 25 bits (all 4 levels), with the sidenote that displacements that result in the kernel image straddling a 1GB/32MB/512MB alignment boundary (for 4KB/16KB/64KB granule kernels, respectively) are not allowed, and will be rounded up to an acceptable value. If CONFIG_RANDOMIZE_MODULE_REGION_FULL is enabled, the module region is randomized independently from the core kernel. This makes it less likely that the location of core kernel data structures can be determined by an adversary, but causes all function calls from modules into the core kernel to be resolved via entries in the module PLTs. If CONFIG_RANDOMIZE_MODULE_REGION_FULL is not enabled, the module region is randomized by choosing a page aligned 128 MB region inside the interval [_etext - 128 MB, _stext + 128 MB). This gives between 10 and 14 bits of entropy (depending on page size), independently of the kernel randomization, but still guarantees that modules are within the range of relative branch and jump instructions (with the caveat that, since the module region is shared with other uses of the vmalloc area, modules may need to be loaded further away if the module region is exhausted) Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Diffstat (limited to 'arch/arm64/mm/kasan_init.c')
-rw-r--r--arch/arm64/mm/kasan_init.c17
1 files changed, 14 insertions, 3 deletions
diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
index 7f10cc91fa8a..56e19d150c21 100644
--- a/arch/arm64/mm/kasan_init.c
+++ b/arch/arm64/mm/kasan_init.c
@@ -129,12 +129,16 @@ static void __init clear_pgds(unsigned long start,
void __init kasan_init(void)
{
u64 kimg_shadow_start, kimg_shadow_end;
+ u64 mod_shadow_start, mod_shadow_end;
struct memblock_region *reg;
int i;
kimg_shadow_start = (u64)kasan_mem_to_shadow(_text);
kimg_shadow_end = (u64)kasan_mem_to_shadow(_end);
+ mod_shadow_start = (u64)kasan_mem_to_shadow((void *)MODULES_VADDR);
+ mod_shadow_end = (u64)kasan_mem_to_shadow((void *)MODULES_END);
+
/*
* We are going to perform proper setup of shadow memory.
* At first we should unmap early shadow (clear_pgds() call bellow).
@@ -158,13 +162,20 @@ void __init kasan_init(void)
* with PMD table mappings at the edges of the shadow region for the
* kernel image.
*/
- if (ARM64_SWAPPER_USES_SECTION_MAPS)
+ if (ARM64_SWAPPER_USES_SECTION_MAPS) {
+ kimg_shadow_start = round_down(kimg_shadow_start,
+ SWAPPER_BLOCK_SIZE);
kimg_shadow_end = round_up(kimg_shadow_end, SWAPPER_BLOCK_SIZE);
+ }
kasan_populate_zero_shadow((void *)KASAN_SHADOW_START,
- kasan_mem_to_shadow((void *)MODULES_VADDR));
+ (void *)mod_shadow_start);
kasan_populate_zero_shadow((void *)kimg_shadow_end,
- kasan_mem_to_shadow((void *)PAGE_OFFSET));
+ kasan_mem_to_shadow((void *)PAGE_OFFSET));
+
+ if (kimg_shadow_start > mod_shadow_end)
+ kasan_populate_zero_shadow((void *)mod_shadow_end,
+ (void *)kimg_shadow_start);
for_each_memblock(memory, reg) {
void *start = (void *)__phys_to_virt(reg->base);