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Date: Sun,  3 Sep 2017 13:07:53 +0100
From: Ard Biesheuvel <ard.biesheuvel@...aro.org>
To: linux-arm-kernel@...ts.infradead.org,
	kernel-hardening@...ts.openwall.com
Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Arnd Bergmann <arnd@...db.de>,
	Nicolas Pitre <nico@...aro.org>,
	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: [PATCH v2 25/29] ARM: decompressor: explicitly map decompressor binary cacheable

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>
---
 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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