From e2b32e6785138d92d2a40e0d0473575c8c7310a2 Mon Sep 17 00:00:00 2001
From: Kees Cook <keescook@chromium.org>
Date: Tue, 25 Feb 2014 16:59:17 -0800
Subject: [PATCH 1/2] 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>
---
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 7116fda7077f..580a60cabd9b 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 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
From 9dd721c6dbfc310f94306902611f86dda87a45fa Mon Sep 17 00:00:00 2001
From: Kees Cook <keescook@chromium.org>
Date: Mon, 10 Mar 2014 13:42:48 -0700
Subject: [PATCH 2/2] x86, kaslr: fix module lock ordering problem
There was a potential lock ordering problem with the module kASLR patch
("x86, kaslr: randomize module base load address"). This patch removes
the usage of the module_mutex and creates a new mutex to protect the
module base address offset value.
Chain exists of:
text_mutex --> kprobe_insn_slots.mutex --> module_mutex
[ 0.515561] Possible unsafe locking scenario:
[ 0.515561]
[ 0.515561] CPU0 CPU1
[ 0.515561] ---- ----
[ 0.515561] lock(module_mutex);
[ 0.515561] lock(kprobe_insn_slots.mutex);
[ 0.515561] lock(module_mutex);
[ 0.515561] lock(text_mutex);
[ 0.515561]
[ 0.515561] *** DEADLOCK ***
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Andy Honig <ahonig@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
---
arch/x86/kernel/module.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c
index 49483137371f..e69f9882bf95 100644
--- a/arch/x86/kernel/module.c
+++ b/arch/x86/kernel/module.c
@@ -48,6 +48,9 @@ do { \
static unsigned long module_load_offset;
static int randomize_modules = 1;
+/* Mutex protects the module_load_offset. */
+static DEFINE_MUTEX(module_kaslr_mutex);
+
static int __init parse_nokaslr(char *p)
{
randomize_modules = 0;
@@ -58,7 +61,7 @@ early_param("nokaslr", parse_nokaslr);
static unsigned long int get_module_load_offset(void)
{
if (randomize_modules) {
- mutex_lock(&module_mutex);
+ mutex_lock(&module_kaslr_mutex);
/*
* Calculate the module_load_offset the first time this
* code is called. Once calculated it stays the same until
@@ -67,7 +70,7 @@ static unsigned long int get_module_load_offset(void)
if (module_load_offset == 0)
module_load_offset =
(get_random_int() % 1024 + 1) * PAGE_SIZE;
- mutex_unlock(&module_mutex);
+ mutex_unlock(&module_kaslr_mutex);
}
return module_load_offset;
}