Commit d5e57437 authored Mar 21, 2016 by Ard Biesheuvel Committed by Catalin Marinas Mar 24, 2016

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>

parent f09f1bac

arch/arm64/kernel/head.S

+2 −2

Original line number	Diff line number	Diff line
		@@ -732,7 +732,7 @@ ENTRY(__early_cpu_boot_status)
		*/
		.section ".idmap.text", "ax"
		__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
		ubfx x2, x1, #ID_AA64MMFR0_TGRAN_SHIFT, 4
		cmp x2, #ID_AA64MMFR0_TGRAN_SUPPORTED
		@@ -760,7 +760,7 @@ __enable_mmu:
		* to take into account by discarding the current kernel mapping and
		* creating a new one.
		*/
		msr sctlr_el1, x18 // disable the MMU
		msr sctlr_el1, x22 // disable the MMU
		isb
		bl __create_page_tables // recreate kernel mapping

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