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Date: Thu, 5 May 2016 15:13:56 -0700
From: Kees Cook <keescook@...omium.org>
To: Ingo Molnar <mingo@...nel.org>
Cc: Kees Cook <keescook@...omium.org>,
Yinghai Lu <yinghai@...nel.org>,
Ingo Molnar <mingo@...hat.com>,
Baoquan He <bhe@...hat.com>,
"H. Peter Anvin" <hpa@...or.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 v6 11/11] 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/kaslr.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
index 8cf705826bdc..ace41822d16f 100644
--- a/arch/x86/boot/compressed/kaslr.c
+++ b/arch/x86/boot/compressed/kaslr.c
@@ -464,7 +464,7 @@ void choose_random_location(unsigned char *input_ptr,
*/
unsigned long input = (unsigned long)input_ptr;
unsigned long output = (unsigned long)*output_ptr;
- unsigned long random_addr;
+ unsigned long random_addr, min_addr;
/* By default, keep output position unchanged. */
*virt_addr = *output_ptr;
@@ -486,8 +486,11 @@ void choose_random_location(unsigned char *input_ptr,
/* Record the various known unsafe memory ranges. */
mem_avoid_init(input, input_size, output);
+ /* Low end should be the smaller of 512M or initial location. */
+ min_addr = min(output, 512UL << 20);
+
/* Walk e820 and find a random address. */
- random_addr = find_random_phys_addr(output, output_size);
+ random_addr = find_random_phys_addr(min_addr, output_size);
if (!random_addr) {
warn("KASLR disabled: could not find suitable E820 region!");
} else {
--
2.6.3
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