Commit-ID: e2b32e6785138d92d2a40e0d0473575c8c7310a2 Gitweb: http://git.kernel.org/tip/e2b32e6785138d92d2a40e0d0473575c8c7310a2 Author: Kees Cook <keesc...@chromium.org> AuthorDate: Tue, 25 Feb 2014 16:59:17 -0800 Committer: H. Peter Anvin <h...@linux.intel.com> CommitDate: Tue, 25 Feb 2014 17:07:26 -0800
x86, kaslr: randomize module base load address Randomize the load address of modules in the kernel to make kASLR effective for modules. Modules can only be loaded within a particular range of virtual address space. This patch adds 10 bits of entropy to the load address by adding 1-1024 * PAGE_SIZE to the beginning range where modules are loaded. The single base offset was chosen because randomizing each module load ends up wasting/fragmenting memory too much. Prior approaches to minimizing fragmentation while doing randomization tend to result in worse entropy than just doing a single base address offset. Example kASLR boot without this change, with a single module loaded: ---[ Modules ]--- 0xffffffffc0000000-0xffffffffc0001000 4K ro GLB x pte 0xffffffffc0001000-0xffffffffc0002000 4K ro GLB NX pte 0xffffffffc0002000-0xffffffffc0004000 8K RW GLB NX pte 0xffffffffc0004000-0xffffffffc0200000 2032K pte 0xffffffffc0200000-0xffffffffff000000 1006M pmd ---[ End Modules ]--- Example kASLR boot after this change, same module loaded: ---[ Modules ]--- 0xffffffffc0000000-0xffffffffc0200000 2M pmd 0xffffffffc0200000-0xffffffffc03bf000 1788K pte 0xffffffffc03bf000-0xffffffffc03c0000 4K ro GLB x pte 0xffffffffc03c0000-0xffffffffc03c1000 4K ro GLB NX pte 0xffffffffc03c1000-0xffffffffc03c3000 8K RW GLB NX pte 0xffffffffc03c3000-0xffffffffc0400000 244K pte 0xffffffffc0400000-0xffffffffff000000 1004M pmd ---[ End Modules ]--- Signed-off-by: Andy Honig <aho...@google.com> Link: http://lkml.kernel.org/r/20140226005916.ga27...@www.outflux.net Signed-off-by: Kees Cook <keesc...@chromium.org> Signed-off-by: H. Peter Anvin <h...@linux.intel.com> --- Documentation/kernel-parameters.txt | 4 ++-- arch/x86/kernel/module.c | 43 ++++++++++++++++++++++++++++++++++--- 2 files changed, 42 insertions(+), 5 deletions(-) diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 7116fda..580a60c 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -2053,8 +2053,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted. IOAPICs that may be present in the system. nokaslr [X86] - Disable kernel base offset ASLR (Address Space - Layout Randomization) if built into the kernel. + Disable kernel and module base offset ASLR (Address + Space Layout Randomization) if built into the kernel. noautogroup Disable scheduler automatic task group creation. diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c index 18be189..4948313 100644 --- a/arch/x86/kernel/module.c +++ b/arch/x86/kernel/module.c @@ -28,6 +28,7 @@ #include <linux/mm.h> #include <linux/gfp.h> #include <linux/jump_label.h> +#include <linux/random.h> #include <asm/page.h> #include <asm/pgtable.h> @@ -43,13 +44,49 @@ do { \ } while (0) #endif +#ifdef CONFIG_RANDOMIZE_BASE +static unsigned long module_load_offset; +static int randomize_modules = 1; + +static int __init parse_nokaslr(char *p) +{ + randomize_modules = 0; + return 0; +} +early_param("nokaslr", parse_nokaslr); + +static unsigned long int get_module_load_offset(void) +{ + if (randomize_modules) { + mutex_lock(&module_mutex); + /* + * Calculate the module_load_offset the first time this + * code is called. Once calculated it stays the same until + * reboot. + */ + if (module_load_offset == 0) + module_load_offset = + (get_random_int() % 1024 + 1) * PAGE_SIZE; + mutex_unlock(&module_mutex); + } + return module_load_offset; +} +#else +static unsigned long int get_module_load_offset(void) +{ + return 0; +} +#endif + void *module_alloc(unsigned long size) { if (PAGE_ALIGN(size) > MODULES_LEN) return NULL; - return __vmalloc_node_range(size, 1, MODULES_VADDR, MODULES_END, - GFP_KERNEL | __GFP_HIGHMEM, PAGE_KERNEL_EXEC, - NUMA_NO_NODE, __builtin_return_address(0)); + return __vmalloc_node_range(size, 1, + MODULES_VADDR + get_module_load_offset(), + MODULES_END, GFP_KERNEL | __GFP_HIGHMEM, + PAGE_KERNEL_EXEC, NUMA_NO_NODE, + __builtin_return_address(0)); } #ifdef CONFIG_X86_32 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
