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Commit f47233c2 authored by Jiri Kosina's avatar Jiri Kosina Committed by Borislav Petkov
Browse files

x86/mm/ASLR: Propagate base load address calculation 



Commit:

  e2b32e67 ("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: default avatarJiri Kosina <jkosina@suse.cz>
Acked-by: default avatarKees 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: default avatarBorislav Petkov <bp@suse.de>
parent bfa76d49

arch/x86/boot/compressed/aslr.c

+33 −1
Original line number Diff line number Diff line
@@ -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,

arch/x86/boot/compressed/misc.c

+2 −1
Original line number Diff line number Diff line
@@ -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);

arch/x86/boot/compressed/misc.h

+4 −2
Original line number Diff line number Diff line
@@ -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)

arch/x86/include/asm/page_types.h

+3 −0
Original line number Diff line number Diff line
@@ -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;

arch/x86/include/uapi/asm/bootparam.h

+1 −0
Original line number Diff line number Diff line
@@ -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