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Date: Mon, 4 Sep 2017 14:47:42 -0400 (EDT)
From: Nicolas Pitre <nicolas.pitre@...aro.org>
To: Ard Biesheuvel <ard.biesheuvel@...aro.org>
cc: linux-arm-kernel@...ts.infradead.org, kernel-hardening@...ts.openwall.com,
Arnd Bergmann <arnd@...db.de>, Russell King <linux@...linux.org.uk>,
Kees Cook <keescook@...omium.org>, Thomas Garnier <thgarnie@...gle.com>,
Marc Zyngier <marc.zyngier@....com>, Mark Rutland <mark.rutland@....com>,
Tony Lindgren <tony@...mide.com>, Matt Fleming <matt@...eblueprint.co.uk>,
Dave Martin <dave.martin@....com>
Subject: Re: [PATCH v2 25/29] ARM: decompressor: explicitly map decompressor
binary cacheable
On Sun, 3 Sep 2017, Ard Biesheuvel wrote:
> When randomizing the kernel load address, there may be a large
> distance in memory between the decompressor binary and its payload
> and the destination area in memory. Ensure that the decompressor
> itself is mapped cacheable in this case, by tweaking the existing
> routine that takes care of this for XIP decompressors.
>
> Cc: Russell King <linux@...linux.org.uk>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Acked-by: Nicolas Pitre <nico@...aro.org>
> ---
> arch/arm/boot/compressed/head.S | 16 ++++++++++------
> 1 file changed, 10 insertions(+), 6 deletions(-)
>
> diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
> index 5884e8151376..583cc6899d98 100644
> --- a/arch/arm/boot/compressed/head.S
> +++ b/arch/arm/boot/compressed/head.S
> @@ -706,20 +706,24 @@ __setup_mmu: sub r3, r4, #16384 @ Page directory size
> teq r0, r2
> bne 1b
> /*
> - * If ever we are running from Flash, then we surely want the cache
> - * to be enabled also for our execution instance... We map 2MB of it
> - * so there is no map overlap problem for up to 1 MB compressed kernel.
> - * If the execution is in RAM then we would only be duplicating the above.
> + * Make sure our entire executable image (including payload) is mapped
> + * cacheable, in case it is located outside the region we covered above.
> + * (This may be the case if running from flash or with randomization enabled)
> + * If the regions happen to overlap, we just duplicate some of the above.
> */
> orr r1, r6, #0x04 @ ensure B is set for this
> orr r1, r1, #3 << 10
> mov r2, pc
> + adr_l r9, _end
> mov r2, r2, lsr #20
> + mov r9, r9, lsr #20
> orr r1, r1, r2, lsl #20
> add r0, r3, r2, lsl #2
> - str r1, [r0], #4
> + add r9, r3, r9, lsl #2
> +0: str r1, [r0], #4
> add r1, r1, #1048576
> - str r1, [r0]
> + cmp r0, r9
> + bls 0b
> mov pc, lr
> ENDPROC(__setup_mmu)
>
> --
> 2.11.0
>
>
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