On 24 August 2016 at 19:02, Mark Rutland <mark.rutland@xxxxxxx> wrote:
> When CONFIG_RANDOMIZE_BASE is selected, we modify the page tables to remap the
> kernel at a newly-chosen VA range. We do this with the MMU disabled, but do not
> invalidate TLBs prior to re-enabling the MMU with the new tables. Thus the old
> mappings entries may still live in TLBs, and we risk violating
> Break-Before-Make requirements, leading to TLB conflicts and/or other issues.
>
> We invalidate TLBs when we uninsall the idmap in early setup code, but prior to
> this we are subject to issues relating to the Break-Before-Make violation.
>
> Avoid these issues by invalidating the TLBs before the new mappings can be
> used by the hardware.
>
> Fixes: f80fb3a3d50843a4 ("arm64: add support for kernel ASLR")
> Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Will Deacon <will.deacon@xxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
Ah yes, brown paper bag time for me.
Acked-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> ---
> arch/arm64/kernel/head.S | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
> index b77f583..3e7b050 100644
> --- a/arch/arm64/kernel/head.S
> +++ b/arch/arm64/kernel/head.S
> @@ -757,6 +757,9 @@ ENTRY(__enable_mmu)
> isb
> bl __create_page_tables // recreate kernel mapping
>
> + tlbi vmalle1 // Remove any stale TLB entries
> + dsb nsh
> +
> msr sctlr_el1, x19 // re-enable the MMU
> isb
> ic iallu // flush instructions fetched
> --
> 2.7.4
>
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