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Message-Id: <20170814125411.22604-27-ard.biesheuvel@linaro.org>
Date: Mon, 14 Aug 2017 13:54:07 +0100
From: Ard Biesheuvel <ard.biesheuvel@...aro.org>
To: kernel-hardening@...ts.openwall.com
Cc: linux-arm-kernel@...ts.infradead.org,
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 26/30] ARM: decompressor: add KASLR support
Add support to the decompressor to load the kernel at a randomized
offset, and invoke the kernel proper while passing on the information
about the offset at which the kernel was loaded.
This implementation was created with the UEFI stub in mind (which has
a rich execution environment that provides access to the platforms
random number generators), which will assign the kaslr_offset variable
directly. However, to allow other bootloaders to use this facility,
the KASLR offset is exposed via a zImage header field as well.
Cc: Russell King <linux@...linux.org.uk>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
---
arch/arm/boot/compressed/head.S | 8 ++++++
arch/arm/include/asm/zimage.h | 30 ++++++++++++++++++--
2 files changed, 36 insertions(+), 2 deletions(-)
diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
index e451738d8954..7111a2cbef95 100644
--- a/arch/arm/boot/compressed/head.S
+++ b/arch/arm/boot/compressed/head.S
@@ -200,6 +200,10 @@ not_angel:
*/
mov r4, pc
and r4, r4, #0xf8000000
+#ifdef CONFIG_RANDOMIZE_BASE
+ ldr_l r0, kaslr_offset
+ add r4, r4, r0
+#endif
/* Determine final kernel image address. */
add r4, r4, #TEXT_OFFSET
#else
@@ -1353,6 +1357,10 @@ __hyp_reentry_vectors:
__enter_kernel:
mov r0, #0 @ must be 0
+#ifdef CONFIG_RANDOMIZE_BASE
+ ldr_l r3, kaslr_offset
+ add r4, r4, #4 @ skip first instruction
+#endif
ARM( mov pc, r4 ) @ call kernel
M_CLASS( add r4, r4, #1 ) @ enter in Thumb mode for M class
THUMB( bx r4 ) @ entry point is always ARM for A/R classes
diff --git a/arch/arm/include/asm/zimage.h b/arch/arm/include/asm/zimage.h
index ff65cc3bb716..554a48ddcfd8 100644
--- a/arch/arm/include/asm/zimage.h
+++ b/arch/arm/include/asm/zimage.h
@@ -10,10 +10,15 @@
#ifndef __ASM_ZIMAGE_H
#define __ASM_ZIMAGE_H
+#include <asm/pgtable.h>
+
#define ZIMAGE_HEADER_MAGIC 0x016f2818
#define ZIMAGE_OPTIONAL_HEADER_MAGIC 0xe7fedef0
-#if defined(__ASSEMBLY__) && !defined(LINKER_SCRIPT)
+#define ZIMAGE_OPT_HDR_ID_KASLR 0x1
+
+#ifndef LINKER_SCRIPT
+#ifdef __ASSEMBLY__
.macro __ZIMAGE_HEADER
.word _magic_sig @ Magic numbers to help the loader
@@ -31,9 +36,30 @@
* Each header starts with a u16[2] containing id and size of the
* entire header, including the u16[] itself.
*/
+
+#ifdef CONFIG_RANDOMIZE_BASE
+0: .short ZIMAGE_OPT_HDR_ID_KASLR
+ .short __kaslr_hdr_size
+
+ /*
+ * The KASLR header carries the information needed by the bootloader
+ * to choose a randomization offset, and record it in the offset
+ * field below.
+ */
+ENTRY(kaslr_offset)
+ .long 0 @ kaslr offset
+ .long CONFIG_PAGE_OFFSET @ page offset
+ .long VMALLOC_DEFAULT_BASE @ start of vmalloc area
+ .long SECTION_SIZE @ kaslr granularity
+ .set __kaslr_hdr_size, . - 0b
+#endif
+
.long 0xffffffff @ end of optional headers
.popsection
.endm
-#endif
+#else /* __ASSEMBLY__ */
+extern u32 kaslr_offset;
+#endif /* __ASSEMBLY__ */
+#endif /* LINKER_SCRIPT */
#endif
--
2.11.0
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