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arm64: kaslr: use callee saved register to preserve SCTLR across C call 

The KASLR code incorrectly expects the contents of x18 to be preserved
across a call into C code, and uses it to stash the contents of SCTLR_EL1
before enabling the MMU. If the MMU needs to be disabled again to create
the randomized kernel mapping, x18 is written back to SCTLR_EL1, which is
likely to crash the system if x18 has been clobbered by kasan_early_init()
or kaslr_early_init(). So use x22 instead, which is not in use so far in
head.S

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Ard Biesheuvel 2016-03-21 18:35:11 +01:00 committed by Catalin Marinas
parent f09f1bacfe
commit d5e5743797
1 changed files with 2 additions and 2 deletions
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4
arch/arm64/kernel/head.S
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@ -732,7 +732,7 @@ ENTRY(__early_cpu_boot_status)
*/ */
.section ".idmap.text", "ax" .section ".idmap.text", "ax"
__enable_mmu: __enable_mmu:
mrs x18, sctlr_el1 // preserve old SCTLR_EL1 value mrs x22, sctlr_el1 // preserve old SCTLR_EL1 value
mrs x1, ID_AA64MMFR0_EL1 mrs x1, ID_AA64MMFR0_EL1
ubfx x2, x1, #ID_AA64MMFR0_TGRAN_SHIFT, 4 ubfx x2, x1, #ID_AA64MMFR0_TGRAN_SHIFT, 4
cmp x2, #ID_AA64MMFR0_TGRAN_SUPPORTED cmp x2, #ID_AA64MMFR0_TGRAN_SUPPORTED
@ -760,7 +760,7 @@ __enable_mmu:
* to take into account by discarding the current kernel mapping and * to take into account by discarding the current kernel mapping and
* creating a new one. * creating a new one.
*/ */
msr sctlr_el1, x18 // disable the MMU msr sctlr_el1, x22 // disable the MMU
isb isb
bl __create_page_tables // recreate kernel mapping bl __create_page_tables // recreate kernel mapping