Messages in this thread Patch in this message | | | From | Kees Cook <> | Subject | [PATCH v8 4/4] x86/KASLR: Allow randomization below load address | Date | Tue, 10 May 2016 10:19:15 -0700 |
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From: Yinghai Lu <yinghai@kernel.org>
Currently the physical randomization's lower boundary is the original kernel 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 whatever 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@kernel.org> [kees: rewrote changelog, refactor to use min()] Signed-off-by: Kees Cook <keescook@chromium.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 d0a823df183b..304c5c369aff 100644 --- a/arch/x86/boot/compressed/kaslr.c +++ b/arch/x86/boot/compressed/kaslr.c @@ -492,7 +492,7 @@ void choose_random_location(unsigned long input, unsigned long output_size, unsigned long *virt_addr) { - unsigned long random_addr; + unsigned long random_addr, min_addr; /* By default, keep output position unchanged. */ *virt_addr = *output; @@ -517,8 +517,11 @@ void choose_random_location(unsigned long input, /* 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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