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Date: Thu, 14 Apr 2016 15:29:14 -0700
From: Kees Cook <keescook@...omium.org>
To: Ingo Molnar <mingo@...nel.org>
Cc: Kees Cook <keescook@...omium.org>,
Yinghai Lu <yinghai@...nel.org>,
Baoquan He <bhe@...hat.com>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Matt Redfearn <matt.redfearn@...tec.com>,
x86@...nel.org,
"H. Peter Anvin" <hpa@...or.com>,
Ingo Molnar <mingo@...hat.com>,
Borislav Petkov <bp@...en8.de>,
Vivek Goyal <vgoyal@...hat.com>,
Andy Lutomirski <luto@...nel.org>,
lasse.collin@...aani.org,
Andrew Morton <akpm@...ux-foundation.org>,
Dave Young <dyoung@...hat.com>,
kernel-hardening@...ts.openwall.com,
LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH v5 21/21] x86, KASLR: Allow randomization below load address
From: Yinghai Lu <yinghai@...nel.org>
Currently the physical randomization's lower boundary is the load
address. For bootloaders that load kernels into very high memory
(e.g. kexec), this means randomization takes place in a very small window
at the top of memory, ignoring the large region of physical memory below
the load address.
Since mem_avoid is already correctly tracking the regions that must be
avoided, this patch changes the minimum address to which ever is less:
512M (to conservatively avoid unknown things in lower memory) or the
load address. Now, for example, if the kernel is loaded at 8G, [512M,
8G) will be added into possible physical memory positions.
Signed-off-by: Yinghai Lu <yinghai@...nel.org>
[kees: rewrote changelog, refactor to use min()]
Signed-off-by: Kees Cook <keescook@...omium.org>
---
arch/x86/boot/compressed/aslr.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/arch/x86/boot/compressed/aslr.c b/arch/x86/boot/compressed/aslr.c
index e83d3bb3808b..864a51863b45 100644
--- a/arch/x86/boot/compressed/aslr.c
+++ b/arch/x86/boot/compressed/aslr.c
@@ -459,7 +459,8 @@ void choose_kernel_location(unsigned char *input,
unsigned long output_size,
unsigned char **virt_offset)
{
- unsigned long random;
+ unsigned long random, min_addr;
+
*virt_offset = (unsigned char *)LOAD_PHYSICAL_ADDR;
#ifdef CONFIG_HIBERNATION
@@ -480,8 +481,11 @@ void choose_kernel_location(unsigned char *input,
mem_avoid_init((unsigned long)input, input_size,
(unsigned long)*output);
+ /* Low end should be the smaller of 512M or initial location. */
+ min_addr = min((unsigned long)*output, 512UL << 20);
+
/* Walk e820 and find a random address. */
- random = find_random_phy_addr((unsigned long)*output, output_size);
+ random = find_random_phy_addr(min_addr, output_size);
if (!random)
debug_putstr("KASLR could not find suitable E820 region...\n");
else {
--
2.6.3
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