x86/mm/ASLR: Propagate base load address calculation

Commit:

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

makes the base address for module to be unconditionally randomized in
case when CONFIG_RANDOMIZE_BASE is defined and "nokaslr" option isn't
present on the commandline.

This is not consistent with how choose_kernel_location() decides whether
it will randomize kernel load base.

Namely, CONFIG_HIBERNATION disables kASLR (unless "kaslr" option is
explicitly specified on kernel commandline), which makes the state space
larger than what module loader is looking at. IOW CONFIG_HIBERNATION &&
CONFIG_RANDOMIZE_BASE is a valid config option, kASLR wouldn't be applied
by default in that case, but module loader is not aware of that.

Instead of fixing the logic in module.c, this patch takes more generic
aproach. It introduces a new bootparam setup data_type SETUP_KASLR and
uses that to pass the information whether kaslr has been applied during
kernel decompression, and sets a global 'kaslr_enabled' variable
accordingly, so that any kernel code (module loading, livepatching, ...)
can make decisions based on its value.

x86 module loader is converted to make use of this flag.

Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: "H. Peter Anvin" <hpa@linux.intel.com>
Link: https://lkml.kernel.org/r/alpine.LNX.2.00.1502101411280.10719@pobox.suse.cz
[ Always dump correct kaslr status when panicking ]
Signed-off-by: Borislav Petkov <bp@suse.de>

diff --git a/arch/x86/boot/compressed/aslr.c b/arch/x86/boot/compressed/aslr.c
index bb1376381985edb9f96e49c0a1b0269e56bd0f9e..7083c16cccba0b2b144ea5e03e160ebafe81e855 100644 (file)
--- a/arch/x86/boot/compressed/aslr.c
+++ b/arch/x86/boot/compressed/aslr.c
@@ -14,6 +14,13 @@
 static const char build_str[] = UTS_RELEASE " (" LINUX_COMPILE_BY "@"
                LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION;
 
+struct kaslr_setup_data {
+       __u64 next;
+       __u32 type;
+       __u32 len;
+       __u8 data[1];
+} kaslr_setup_data;
+
 #define I8254_PORT_CONTROL     0x43
 #define I8254_PORT_COUNTER0    0x40
 #define I8254_CMD_READBACK     0xC0
@@ -295,7 +302,29 @@ static unsigned long find_random_addr(unsigned long minimum,
        return slots_fetch_random();
 }
 
-unsigned char *choose_kernel_location(unsigned char *input,
+static void add_kaslr_setup_data(struct boot_params *params, __u8 enabled)
+{
+       struct setup_data *data;
+
+       kaslr_setup_data.type = SETUP_KASLR;
+       kaslr_setup_data.len = 1;
+       kaslr_setup_data.next = 0;
+       kaslr_setup_data.data[0] = enabled;
+
+       data = (struct setup_data *)(unsigned long)params->hdr.setup_data;
+
+       while (data && data->next)
+               data = (struct setup_data *)(unsigned long)data->next;
+
+       if (data)
+               data->next = (unsigned long)&kaslr_setup_data;
+       else
+               params->hdr.setup_data = (unsigned long)&kaslr_setup_data;
+
+}
+
+unsigned char *choose_kernel_location(struct boot_params *params,
+                                     unsigned char *input,
                                      unsigned long input_size,
                                      unsigned char *output,
                                      unsigned long output_size)
@@ -306,14 +335,17 @@ unsigned char *choose_kernel_location(unsigned char *input,
 #ifdef CONFIG_HIBERNATION
        if (!cmdline_find_option_bool("kaslr")) {
                debug_putstr("KASLR disabled by default...\n");
+               add_kaslr_setup_data(params, 0);
                goto out;
        }
 #else
        if (cmdline_find_option_bool("nokaslr")) {
                debug_putstr("KASLR disabled by cmdline...\n");
+               add_kaslr_setup_data(params, 0);
                goto out;
        }
 #endif
+       add_kaslr_setup_data(params, 1);
 
        /* Record the various known unsafe memory ranges. */
        mem_avoid_init((unsigned long)input, input_size,

diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index a950864a64dab3d558197c77bef3c56a07961494..5903089c818f6843b9d1cc7c83507cf0d28a3e26 100644 (file)
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -401,7 +401,8 @@ 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 24e3e569a13ce9bf1ba620811ff4b09d6fa6e32d..6d67307430249d609bd60efcca28b13aa9ccbb92 100644 (file)
--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -56,7 +56,8 @@ 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 *params,
+                                     unsigned char *input,
                                      unsigned long input_size,
                                      unsigned char *output,
                                      unsigned long output_size);
@@ -64,7 +65,8 @@ 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 *params,
+                                     unsigned char *input,
                                      unsigned long input_size,
                                      unsigned char *output,
                                      unsigned long output_size)

diff --git a/arch/x86/include/asm/page_types.h b/arch/x86/include/asm/page_types.h
index f97fbe3abb67f5059d4e6f0a37261d6113df19de..3d43ce36eaba779ef19c409f9605e944dfb43aa4 100644 (file)
--- a/arch/x86/include/asm/page_types.h
+++ b/arch/x86/include/asm/page_types.h
@@ -3,6 +3,7 @@
 
 #include <linux/const.h>
 #include <linux/types.h>
+#include <asm/bootparam.h>
 
 /* PAGE_SHIFT determines the page size */
 #define PAGE_SHIFT     12
@@ -51,6 +52,8 @@ extern int devmem_is_allowed(unsigned long pagenr);
 extern unsigned long max_low_pfn_mapped;
 extern unsigned long max_pfn_mapped;
 
+extern bool kaslr_enabled;
+
 static inline phys_addr_t get_max_mapped(void)
 {
        return (phys_addr_t)max_pfn_mapped << PAGE_SHIFT;

diff --git a/arch/x86/include/uapi/asm/bootparam.h b/arch/x86/include/uapi/asm/bootparam.h
index 225b0988043a0a78ac9092a9af7a265122c685cd..44e6dd7e36a23becd48def85b218b1d70ac938e6 100644 (file)
--- a/arch/x86/include/uapi/asm/bootparam.h
+++ b/arch/x86/include/uapi/asm/bootparam.h
@@ -7,6 +7,7 @@
 #define SETUP_DTB                      2
 #define SETUP_PCI                      3
 #define SETUP_EFI                      4
+#define SETUP_KASLR                    5
 
 /* ram_size flags */
 #define RAMDISK_IMAGE_START_MASK       0x07FF

diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c
index e69f9882bf95a942ae1ce0f75efbf07301c9adc3..c3c59a3a14adb186b9bf5a54f1c11f45a055a39e 100644 (file)
--- a/arch/x86/kernel/module.c
+++ b/arch/x86/kernel/module.c
@@ -32,6 +32,7 @@
 
 #include <asm/page.h>
 #include <asm/pgtable.h>
+#include <asm/page_types.h>
 
 #if 0
 #define DEBUGP(fmt, ...)                               \
@@ -46,21 +47,13 @@ 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 ab4734e5411d76daa06624afc6d1eb4325d1a128..16b6043cb073404e3bdf14cd7d982deb4d813b1d 100644 (file)
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -121,6 +121,8 @@
 unsigned long max_low_pfn_mapped;
 unsigned long max_pfn_mapped;
 
+bool __read_mostly kaslr_enabled = false;
+
 #ifdef CONFIG_DMI
 RESERVE_BRK(dmi_alloc, 65536);
 #endif
@@ -424,6 +426,11 @@ static void __init reserve_initrd(void)
 }
 #endif /* CONFIG_BLK_DEV_INITRD */
 
+static void __init parse_kaslr_setup(u64 pa_data, u32 data_len)
+{
+       kaslr_enabled = (bool)(pa_data + sizeof(struct setup_data));
+}
+
 static void __init parse_setup_data(void)
 {
        struct setup_data *data;
@@ -451,6 +458,9 @@ static void __init parse_setup_data(void)
                case SETUP_EFI:
                        parse_efi_setup(pa_data, data_len);
                        break;
+               case SETUP_KASLR:
+                       parse_kaslr_setup(pa_data, data_len);
+                       break;
                default:
                        break;
                }
@@ -833,10 +843,14 @@ 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;
 }