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| author | Kees Cook <keescook@chromium.org> | 2014-02-25 16:59:17 -0800 |
|---|---|---|
| committer | H. Peter Anvin <hpa@linux.intel.com> | 2014-02-25 17:07:26 -0800 |
| commit | e2b32e6785138d92d2a40e0d0473575c8c7310a2 (patch) | |
| tree | 1522d169745c58697194f3656bb437363bdfcd78 /arch/x86/kernel/module.c | |
| parent | cfbf8d4857c26a8a307fb7cd258074c9dcd8c691 (diff) | |
| download | linux-e2b32e6785138d92d2a40e0d0473575c8c7310a2.tar.gz | |
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 <ahonig@google.com> Link: http://lkml.kernel.org/r/20140226005916.GA27083@www.outflux.net Signed-off-by: Kees Cook <keescook@chromium.org> Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Diffstat (limited to 'arch/x86/kernel/module.c')
| -rw-r--r-- | arch/x86/kernel/module.c | 43 |
1 files changed, 40 insertions, 3 deletions
diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c index 18be189368bb..49483137371f 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 |