From: Yinghai Lu <ying...@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 <ying...@kernel.org>
[kees: rewrote changelog, refactor to use min()]
Signed-off-by: Kees Cook <keesc...@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 def1da9e7863..d972a026d44c 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;
@@ -514,8 +514,11 @@ 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
