[PATCH] x86/mm/ASLR: Propagate ASLR status to kernel proper

Borislav Petkov
2015-04-01T11:01:31Z

From: Borislav Petkov <bp@suse.de>

Commit

e2b32e678513 ("x86, kaslr: randomize module base load address")

made module base address randomization unconditional and didn't regard
disabled KASLR due to CONFIG_HIBERNATION and command line option
"nokaslr". For more info see (now reverted) commit:

f47233c2d34f ("x86/mm/ASLR: Propagate base load address calculation")

In order to propagate ASLR status to kernel proper, we need a single bit
in boot_params.hdr.loadflags and we've chosen bit 1 thus leaving the
top-down allocated bits for bits supposed to be used by the bootloader.

Originally-by: Jiri Kosina <jkosina@suse.cz>
Suggested-by: "H. Peter Anvin" <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
---
Documentation/x86/boot.txt | 6 ++++++
arch/x86/boot/compressed/aslr.c | 5 ++++-
arch/x86/boot/compressed/misc.c | 5 ++++-
arch/x86/boot/compressed/misc.h | 6 ++++--
arch/x86/include/asm/setup.h | 5 +++++
arch/x86/include/uapi/asm/bootparam.h | 1 +
arch/x86/kernel/module.c | 11 ++---------
arch/x86/kernel/setup.c | 12 ++++++++----
8 files changed, 34 insertions(+), 17 deletions(-)

diff --git a/Documentation/x86/boot.txt b/Documentation/x86/boot.txt
index a75e3adaa39d..0e1756e680c1 100644
--- a/Documentation/x86/boot.txt
+++ b/Documentation/x86/boot.txt
@@ -406,6 +406,12 @@ Protocol: 2.00+
- If 0, the protected-mode code is loaded at 0x10000.
- If 1, the protected-mode code is loaded at 0x100000.

+ Bit 1 (read): ALSR_FLAG
+ - Used internally by the compressed kernel to communicate
+ ASLR status to kernel proper.
+ If 1, ASLR enabled.
+ If 0, ASLR disabled.
+
Bit 5 (write): QUIET_FLAG
- If 0, print early messages.
- If 1, suppress early messages.
diff --git a/arch/x86/boot/compressed/aslr.c b/arch/x86/boot/compressed/aslr.c
index bb1376381985..370e47d763b0 100644
--- a/arch/x86/boot/compressed/aslr.c
+++ b/arch/x86/boot/compressed/aslr.c
@@ -295,7 +295,8 @@ static unsigned long find_random_addr(unsigned long minimum,
return slots_fetch_random();
}

-unsigned char *choose_kernel_location(unsigned char *input,
+unsigned char *choose_kernel_location(struct boot_params *boot_params,
+ unsigned char *input,
unsigned long input_size,
unsigned char *output,
unsigned long output_size)
@@ -315,6 +316,8 @@ unsigned char *choose_kernel_location(unsigned char *input,
}
#endif

+ boot_params->hdr.loadflags |= ASLR_FLAG;
+
/* Record the various known unsafe memory ranges. */
mem_avoid_init((unsigned long)input, input_size,
(unsigned long)output, output_size);
diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index a950864a64da..ca83518e405e 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -377,6 +377,9 @@ asmlinkage __visible void *decompress_kernel(void *rmode, memptr heap,

real_mode = rmode;

+ /* Clear it for solely in-kernel use */
+ real_mode->hdr.loadflags &= ~ASLR_FLAG;
+
sanitize_boot_params(real_mode);

if (real_mode->screen_info.orig_video_mode == 7) {
@@ -401,7 +404,7 @@ asmlinkage __visible void *decompress_kernel(void *rmode, memptr heap,
* the entire decompressed kernel plus relocation table, or the
* entire decompressed kernel plus .bss and .brk sections.
*/
- output = choose_kernel_location(input_data, input_len, output,
+ output = choose_kernel_location(real_mode, input_data, input_len, output,
output_len > run_size ? output_len
: run_size);

diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
index 04477d68403f..89dd0d78013a 100644
--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -57,7 +57,8 @@ int cmdline_find_option_bool(const char *option);

#if CONFIG_RANDOMIZE_BASE
/* aslr.c */
-unsigned char *choose_kernel_location(unsigned char *input,
+unsigned char *choose_kernel_location(struct boot_params *boot_params,
+ unsigned char *input,
unsigned long input_size,
unsigned char *output,
unsigned long output_size);
@@ -65,7 +66,8 @@ unsigned char *choose_kernel_location(unsigned char *input,
bool has_cpuflag(int flag);
#else
static inline
-unsigned char *choose_kernel_location(unsigned char *input,
+unsigned char *choose_kernel_location(struct boot_params *boot_params,
+ unsigned char *input,
unsigned long input_size,
unsigned char *output,
unsigned long output_size)
diff --git a/arch/x86/include/asm/setup.h b/arch/x86/include/asm/setup.h
index ff4e7b236e21..87097428a44d 100644
--- a/arch/x86/include/asm/setup.h
+++ b/arch/x86/include/asm/setup.h
@@ -66,6 +66,11 @@ static inline void x86_ce4100_early_setup(void) { }
*/
extern struct boot_params boot_params;

+static inline bool kaslr_enabled(void)
+{
+ return !!(boot_params.hdr.loadflags & ASLR_FLAG);
+}
+
/*
* Do NOT EVER look at the BIOS memory size location.
* It does not work on many machines.
diff --git a/arch/x86/include/uapi/asm/bootparam.h b/arch/x86/include/uapi/asm/bootparam.h
index 225b0988043a..cd495e5d7d9d 100644
--- a/arch/x86/include/uapi/asm/bootparam.h
+++ b/arch/x86/include/uapi/asm/bootparam.h
@@ -15,6 +15,7 @@

/* loadflags */
#define LOADED_HIGH (1<<0)
+#define ASLR_FLAG (1<<1)
#define QUIET_FLAG (1<<5)
#define KEEP_SEGMENTS (1<<6)
#define CAN_USE_HEAP (1<<7)
diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c
index d1ac80b72c72..005c03e93fc5 100644
--- a/arch/x86/kernel/module.c
+++ b/arch/x86/kernel/module.c
@@ -33,6 +33,7 @@

#include <asm/page.h>
#include <asm/pgtable.h>
+#include <asm/setup.h>

#if 0
#define DEBUGP(fmt, ...) \
@@ -47,21 +48,13 @@ do { \

#ifdef CONFIG_RANDOMIZE_BASE
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;
- return 0;
-}
-early_param("nokaslr", parse_nokaslr);
-
static unsigned long int get_module_load_offset(void)
{
- if (randomize_modules) {
+ if (kaslr_enabled()) {
mutex_lock(&module_kaslr_mutex);
/*
* Calculate the module_load_offset the first time this
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 5437af09f204..b14cedb1e1ee 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -832,10 +832,14 @@ static void __init trim_low_memory_range(void)
static int
dump_kernel_offset(struct notifier_block *self, unsigned long v, void *p)
{
- pr_emerg("Kernel Offset: 0x%lx from 0x%lx "
- "(relocation range: 0x%lx-0x%lx)\n",
- (unsigned long)&_text - __START_KERNEL, __START_KERNEL,
- __START_KERNEL_map, MODULES_VADDR-1);
+ if (kaslr_enabled())
+ pr_emerg("Kernel Offset: 0x%lx from 0x%lx (relocation range: 0x%lx-0x%lx)\n",
+ (unsigned long)&_text - __START_KERNEL,
+ __START_KERNEL,
+ __START_KERNEL_map,
+ MODULES_VADDR-1);
+ else
+ pr_emerg("Kernel Offset: disabled\n");

return 0;
}
--
2.3.3