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x86, kaslr: randomize module base load address

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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>
This commit is contained in:
Kees Cook
2014-02-25 16:59:17 -08:00
committed by H. Peter Anvin
parent cfbf8d4857
commit e2b32e6785
2 changed files with 42 additions and 5 deletions
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43
arch/x86/kernel/module.c
View File

@@ -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