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Commit ae89bc64 authored by Tobin C. Harding's avatar Tobin C. Harding Committed by Alistair Strachan
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BACKPORT: printk: hash addresses printed with %p 



Currently there exist approximately 14 000 places in the kernel where
addresses are being printed using an unadorned %p. This potentially
leaks sensitive information regarding the Kernel layout in memory. Many
of these calls are stale, instead of fixing every call lets hash the
address by default before printing. This will of course break some
users, forcing code printing needed addresses to be updated.

Code that _really_ needs the address will soon be able to use the new
printk specifier %px to print the address.

For what it's worth, usage of unadorned %p can be broken down as
follows (thanks to Joe Perches).

$ git grep -E '%p[^A-Za-z0-9]' | cut -f1 -d"/" | sort | uniq -c
   1084 arch
     20 block
     10 crypto
     32 Documentation
   8121 drivers
   1221 fs
    143 include
    101 kernel
     69 lib
    100 mm
   1510 net
     40 samples
      7 scripts
     11 security
    166 sound
    152 tools
      2 virt

Add function ptr_to_id() to map an address to a 32 bit unique
identifier. Hash any unadorned usage of specifier %p and any malformed
specifiers.

Signed-off-by: default avatarTobin C. Harding <me@tobin.cc>
(cherry picked from commit ad67b74d2469d9b82aaa572d76474c95bc484d57)
Signed-off-by: default avatarSandeep Patil <sspatil@android.com>

Bug: 78533979
Test: Build and boot cuttlefish
Test: Runtime tests by enabling CONFIG_TEST_PRINTF
Change-Id: I4a12d890d7b22caa502280d78cb4f6a09c866471
parent 92fc1591

Documentation/printk-formats.txt

+8 −0
Original line number Original line Diff line number Diff line
@@ -31,6 +31,14 @@ return from vsnprintf. 
Raw pointer value SHOULD be printed with %p. The kernel supports

Raw pointer value SHOULD be printed with %p. The kernel supports

the following extended format specifiers for pointer types:

the following extended format specifiers for pointer types:





Pointer Types:



Pointers printed without a specifier extension (i.e unadorned %p) are

hashed to give a unique identifier without leaking kernel addresses to user

space. On 64 bit machines the first 32 bits are zeroed.



	%p	abcdef12 or 00000000abcdef12



Symbols/Function Pointers:

Symbols/Function Pointers:





	%pF	versatile_init+0x0/0x110

	%pF	versatile_init+0x0/0x110

lib/test_printf.c

+70 −38
Original line number Original line Diff line number Diff line
@@ -24,24 +24,6 @@ 
#define PAD_SIZE 16

#define PAD_SIZE 16

#define FILL_CHAR '$'

#define FILL_CHAR '$'





#define PTR1 ((void*)0x01234567)

#define PTR2 ((void*)(long)(int)0xfedcba98)



#if BITS_PER_LONG == 64

#define PTR1_ZEROES "000000000"

#define PTR1_SPACES "         "

#define PTR1_STR "1234567"

#define PTR2_STR "fffffffffedcba98"

#define PTR_WIDTH 16

#else

#define PTR1_ZEROES "0"

#define PTR1_SPACES " "

#define PTR1_STR "1234567"

#define PTR2_STR "fedcba98"

#define PTR_WIDTH 8

#endif

#define PTR_WIDTH_STR stringify(PTR_WIDTH)



static unsigned total_tests __initdata;

static unsigned total_tests __initdata;

static unsigned failed_tests __initdata;

static unsigned failed_tests __initdata;

static char *test_buffer __initdata;

static char *test_buffer __initdata;
@@ -217,30 +199,79 @@ test_string(void) 
	test("a  |   |   ", "%-3.s|%-3.0s|%-3.*s", "a", "b", 0, "c");

	test("a  |   |   ", "%-3.s|%-3.0s|%-3.*s", "a", "b", 0, "c");

}

}





static void __init

#define PLAIN_BUF_SIZE 64	/* leave some space so we don't oops */

plain(void)



#if BITS_PER_LONG == 64



#define PTR_WIDTH 16

#define PTR ((void *)0xffff0123456789ab)

#define PTR_STR "ffff0123456789ab"

#define ZEROS "00000000"	/* hex 32 zero bits */



static int __init

plain_format(void)

{

{

	test(PTR1_ZEROES PTR1_STR " " PTR2_STR, "%p %p", PTR1, PTR2);

	char buf[PLAIN_BUF_SIZE];

	/*

	int nchars;

	 * The field width is overloaded for some %p extensions to



	 * pass another piece of information. For plain pointers, the

	nchars = snprintf(buf, PLAIN_BUF_SIZE, "%p", PTR);

	 * behaviour is slightly odd: One cannot pass either the 0



	 * flag nor a precision to %p without gcc complaining, and if

	if (nchars != PTR_WIDTH || strncmp(buf, ZEROS, strlen(ZEROS)) != 0)

	 * one explicitly gives a field width, the number is no longer

		return -1;

	 * zero-padded.



	 */

	return 0;

	test("|" PTR1_STR PTR1_SPACES "  |  " PTR1_SPACES PTR1_STR "|",

}

	     "|%-*p|%*p|", PTR_WIDTH+2, PTR1, PTR_WIDTH+2, PTR1);



	test("|" PTR2_STR "  |  " PTR2_STR "|",

#else

	     "|%-*p|%*p|", PTR_WIDTH+2, PTR2, PTR_WIDTH+2, PTR2);



#define PTR_WIDTH 8

#define PTR ((void *)0x456789ab)

#define PTR_STR "456789ab"



static int __init

plain_format(void)

{

	/* Format is implicitly tested for 32 bit machines by plain_hash() */

	return 0;

}



#endif	/* BITS_PER_LONG == 64 */



static int __init

plain_hash(void)

{

	char buf[PLAIN_BUF_SIZE];

	int nchars;



	nchars = snprintf(buf, PLAIN_BUF_SIZE, "%p", PTR);



	if (nchars != PTR_WIDTH || strncmp(buf, PTR_STR, PTR_WIDTH) == 0)

		return -1;



	return 0;

}





/*

/*

	 * Unrecognized %p extensions are treated as plain %p, but the

 * We can't use test() to test %p because we don't know what output to expect

	 * alphanumeric suffix is ignored (that is, does not occur in

 * after an address is hashed.

	 * the output.)

 */

 */

	test("|"PTR1_ZEROES PTR1_STR"|", "|%p0y|", PTR1);

static void __init

	test("|"PTR2_STR"|", "|%p0y|", PTR2);

plain(void)

{

	int err;



	err = plain_hash();

	if (err) {

		pr_warn("plain 'p' does not appear to be hashed\n");

		failed_tests++;

		return;

	}



	err = plain_format();

	if (err) {

		pr_warn("hashing plain 'p' has unexpected format\n");

		failed_tests++;

	}

}

}





static void __init

static void __init
@@ -251,6 +282,7 @@ symbol_ptr(void) 
static void __init

static void __init

kernel_ptr(void)

kernel_ptr(void)

{

{

	/* We can't test this without access to kptr_restrict. */

}

}





static void __init

static void __init

lib/vsprintf.c

+74 −7
Original line number Original line Diff line number Diff line
@@ -32,6 +32,8 @@ 
#include <linux/cred.h>

#include <linux/cred.h>

#include <linux/uuid.h>

#include <linux/uuid.h>

#include <net/addrconf.h>

#include <net/addrconf.h>

#include <linux/siphash.h>

#include <linux/compiler.h>

#ifdef CONFIG_BLOCK

#ifdef CONFIG_BLOCK

#include <linux/blkdev.h>

#include <linux/blkdev.h>

#endif

#endif
@@ -1520,6 +1522,73 @@ char *flags_string(char *buf, char *end, void *flags_ptr, const char *fmt) 
	return format_flags(buf, end, flags, names);

	return format_flags(buf, end, flags, names);

}

}





static bool have_filled_random_ptr_key __read_mostly;

static siphash_key_t ptr_key __read_mostly;



static void fill_random_ptr_key(struct random_ready_callback *unused)

{

	get_random_bytes(&ptr_key, sizeof(ptr_key));

	/*

	 * have_filled_random_ptr_key==true is dependent on get_random_bytes().

	 * ptr_to_id() needs to see have_filled_random_ptr_key==true

	 * after get_random_bytes() returns.

	 */

	smp_mb();

	WRITE_ONCE(have_filled_random_ptr_key, true);

}



static struct random_ready_callback random_ready = {

	.func = fill_random_ptr_key

};



static int __init initialize_ptr_random(void)

{

	int ret = add_random_ready_callback(&random_ready);



	if (!ret) {

		return 0;

	} else if (ret == -EALREADY) {

		fill_random_ptr_key(&random_ready);

		return 0;

	}



	return ret;

}

early_initcall(initialize_ptr_random);



/* Maps a pointer to a 32 bit unique identifier. */

static char *ptr_to_id(char *buf, char *end, void *ptr, struct printf_spec spec)

{

	unsigned long hashval;

	const int default_width = 2 * sizeof(ptr);



	if (unlikely(!have_filled_random_ptr_key)) {

		spec.field_width = default_width;

		/* string length must be less than default_width */

		return string(buf, end, "(ptrval)", spec);

	}



#ifdef CONFIG_64BIT

	hashval = (unsigned long)siphash_1u64((u64)ptr, &ptr_key);

	/*

	 * Mask off the first 32 bits, this makes explicit that we have

	 * modified the address (and 32 bits is plenty for a unique ID).

	 */

	hashval = hashval & 0xffffffff;

#else

	hashval = (unsigned long)siphash_1u32((u32)ptr, &ptr_key);

#endif



	spec.flags |= SMALL;

	if (spec.field_width == -1) {

		spec.field_width = default_width;

		spec.flags |= ZEROPAD;

	}

	spec.base = 16;



	return number(buf, end, hashval, spec);

}



/*

/*

 * Show a '%p' thing.  A kernel extension is that the '%p' is followed

 * Show a '%p' thing.  A kernel extension is that the '%p' is followed

 * by an extra set of alphanumeric characters that are extended format

 * by an extra set of alphanumeric characters that are extended format
@@ -1617,6 +1686,9 @@ char *flags_string(char *buf, char *end, void *flags_ptr, const char *fmt) 
 * Note: The difference between 'S' and 'F' is that on ia64 and ppc64

 * Note: The difference between 'S' and 'F' is that on ia64 and ppc64

 * function pointers are really function descriptors, which contain a

 * function pointers are really function descriptors, which contain a

 * pointer to the real address.

 * pointer to the real address.

 *

 * Note: The default behaviour (unadorned %p) is to hash the address,

 * rendering it useful as a unique identifier.

 */

 */

static noinline_for_stack

static noinline_for_stack

char *pointer(const char *fmt, char *buf, char *end, void *ptr,

char *pointer(const char *fmt, char *buf, char *end, void *ptr,
@@ -1727,14 +1799,9 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr, 
	case 'G':

	case 'G':

		return flags_string(buf, end, ptr, fmt);

		return flags_string(buf, end, ptr, fmt);

	}

	}

	spec.flags |= SMALL;

	if (spec.field_width == -1) {

		spec.field_width = default_width;

		spec.flags |= ZEROPAD;

	}

	spec.base = 16;





	return number(buf, end, (unsigned long) ptr, spec);

	/* default is to _not_ leak addresses, hash before printing */

	return ptr_to_id(buf, end, ptr, spec);

}

}





/*

/*