Commit-ID: e066cc47776a89bbdaf4184c0e75f7d389f9ab48 Gitweb: http://git.kernel.org/tip/e066cc47776a89bbdaf4184c0e75f7d389f9ab48 Author: Yinghai Lu <[email protected]> AuthorDate: Wed, 25 May 2016 15:45:34 -0700 Committer: Ingo Molnar <[email protected]> CommitDate: Sun, 26 Jun 2016 12:32:05 +0200
x86/KASLR: Allow randomization below the load address Currently the kernel image physical address 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 to the list of possible physical memory positions. Signed-off-by: Yinghai Lu <[email protected]> [ Rewrote the changelog, refactored the code to use min(). ] Signed-off-by: Kees Cook <[email protected]> Cc: Andrew Morton <[email protected]> Cc: Andrey Ryabinin <[email protected]> Cc: Andy Lutomirski <[email protected]> Cc: Baoquan He <[email protected]> Cc: Borislav Petkov <[email protected]> Cc: Brian Gerst <[email protected]> Cc: Denys Vlasenko <[email protected]> Cc: Dmitry Vyukov <[email protected]> Cc: H. Peter Anvin <[email protected]> Cc: H.J. Lu <[email protected]> Cc: Josh Poimboeuf <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Thomas Gleixner <[email protected]> Link: http://lkml.kernel.org/r/[email protected] [ Edited the changelog some more, plus the code comment as well. ] Signed-off-by: Ingo Molnar <[email protected]> --- arch/x86/boot/compressed/kaslr.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c index 36e2811..749c9e0 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; @@ -510,8 +510,15 @@ void choose_random_location(unsigned long input, /* Record the various known unsafe memory ranges. */ mem_avoid_init(input, input_size, *output); + /* + * Low end of the randomization range should be the + * smaller of 512M or the initial kernel image + * 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 {
