From mboxrd@z Thu Jan 1 00:00:00 1970 Reply-To: kernel-hardening@lists.openwall.com From: Kees Cook Date: Tue, 10 May 2016 10:19:15 -0700 Message-Id: <1462900755-20005-5-git-send-email-keescook@chromium.org> In-Reply-To: <1462900755-20005-1-git-send-email-keescook@chromium.org> References: <1462900755-20005-1-git-send-email-keescook@chromium.org> Subject: [kernel-hardening] [PATCH v8 4/4] x86/KASLR: Allow randomization below load address To: Ingo Molnar Cc: Kees Cook , Yinghai Lu , Borislav Petkov , Baoquan He , Ingo Molnar , "H. Peter Anvin" , Borislav Petkov , Vivek Goyal , Andy Lutomirski , lasse.collin@tukaani.org, Andrew Morton , Dave Young , kernel-hardening@lists.openwall.com, LKML List-ID: From: Yinghai Lu 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 [kees: rewrote changelog, refactor to use min()] Signed-off-by: Kees Cook --- 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