Merge tag 'printk-hash-pointer-4.15-rc2' of git://github.com/tcharding/linux

Pull printk pointer hashing update from Tobin Harding:
"Here is the patch set that implements hashing of printk specifier %p.

First we have two clean up patches then we do the hashing. Hashing is
done via the SipHash algorithm. The next patch adds printk specifier
%px for printing pointers when we _really_ want to see the address i.e
%px is functionally equivalent to %lx. Final patch in the set fixes
KASAN since we break it by hashing %p.

For the record here is the justification for the series:

Currently there exist approximately 14 000 places in the Kernel
where addresses are being printed using an unadorned %p. This
potentially leaks sensitive information about the Kernel layout in
memory. Many of these calls are stale, instead of fixing every call
we hash the address by default before printing. We then add %px to
provide a way to print the actual address. Although this is
achievable using %lx, using %px will assist us if we ever want to
change pointer printing behaviour. %px is more uniquely grep'able
(there are already >50 000 uses of %lx).

The added advantage of hashing %p is that security is now opt-out,
if you _really_ want the address you have to work a little harder
and use %px.

This will of course break some users, forcing code printing needed
addresses to be updated"

[ I do expect this to be an annoyance, and a number of %px users to be
added for debuggability. But nobody is willing to audit existing %p
users for information leaks, and a number of places really only use
the pointer as an object identifier rather than really 'I need the
address'.

IOW - sorry for the inconvenience, but it's the least inconvenient of
the options. - Linus ]

* tag 'printk-hash-pointer-4.15-rc2' of git://github.com/tcharding/linux:
kasan: use %px to print addresses instead of %p
vsprintf: add printk specifier %px
printk: hash addresses printed with %p
vsprintf: refactor %pK code out of pointer()
docs: correct documentation for %pK

Documentation/printk-formats.txt

···
 :Author: Randy Dunlap <[e-mail]>
 :Author: Andrew Murray <[e-mail]>
 
-
 Integer types
 =============
 
···
 
 Raw pointer value SHOULD be printed with %p. The kernel supports
 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. If you _really_
+want the address see %px below.
+
+::
+
+	%p	abcdef12 or 00000000abcdef12
 
 Symbols/Function Pointers
 =========================
···
 	printk("Faulted at %pS\n", (void *)regs->ip);
 	printk(" %s%pB\n", (reliable ? "" : "? "), (void *)*stack);
 
-
 Kernel Pointers
 ===============
 
 ::
 
-	%pK	0x01234567 or 0x0123456789abcdef
+	%pK	01234567 or 0123456789abcdef
 
 For printing kernel pointers which should be hidden from unprivileged
 users. The behaviour of ``%pK`` depends on the ``kptr_restrict sysctl`` - see
 Documentation/sysctl/kernel.txt for more details.
+
+Unmodified Addresses
+====================
+
+::
+
+	%px	01234567 or 0123456789abcdef
+
+For printing pointers when you _really_ want to print the address. Please
+consider whether or not you are leaking sensitive information about the
+Kernel layout in memory before printing pointers with %px. %px is
+functionally equivalent to %lx. %px is preferred to %lx because it is more
+uniquely grep'able. If, in the future, we need to modify the way the Kernel
+handles printing pointers it will be nice to be able to find the call
+sites.
 
 Struct Resources
 ================

lib/test_printf.c

···
 #define PAD_SIZE 16
 #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 failed_tests __initdata;
 static char *test_buffer __initdata;
···
 	test("a  |   |   ", "%-3.s|%-3.0s|%-3.*s", "a", "b", 0, "c");
 }
 
+#define PLAIN_BUF_SIZE 64	/* leave some space so we don't oops */
+
+#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)
+{
+	char buf[PLAIN_BUF_SIZE];
+	int nchars;
+
+	nchars = snprintf(buf, PLAIN_BUF_SIZE, "%p", PTR);
+
+	if (nchars != PTR_WIDTH || strncmp(buf, ZEROS, strlen(ZEROS)) != 0)
+		return -1;
+
+	return 0;
+}
+
+#else
+
+#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;
+}
+
+/*
+ * We can't use test() to test %p because we don't know what output to expect
+ * after an address is hashed.
+ */
 static void __init
 plain(void)
 {
-	test(PTR1_ZEROES PTR1_STR " " PTR2_STR, "%p %p", PTR1, PTR2);
-	/*
-	 * The field width is overloaded for some %p extensions to
-	 * pass another piece of information. For plain pointers, the
-	 * behaviour is slightly odd: One cannot pass either the 0
-	 * flag nor a precision to %p without gcc complaining, and if
-	 * one explicitly gives a field width, the number is no longer
-	 * zero-padded.
-	 */
-	test("|" PTR1_STR PTR1_SPACES "  |  " PTR1_SPACES PTR1_STR "|",
-	     "|%-*p|%*p|", PTR_WIDTH+2, PTR1, PTR_WIDTH+2, PTR1);
-	test("|" PTR2_STR "  |  " PTR2_STR "|",
-	     "|%-*p|%*p|", PTR_WIDTH+2, PTR2, PTR_WIDTH+2, PTR2);
+	int err;
 
-	/*
-	 * Unrecognized %p extensions are treated as plain %p, but the
-	 * alphanumeric suffix is ignored (that is, does not occur in
-	 * the output.)
-	 */
-	test("|"PTR1_ZEROES PTR1_STR"|", "|%p0y|", PTR1);
-	test("|"PTR2_STR"|", "|%p0y|", PTR2);
+	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
 kernel_ptr(void)
 {
+	/* We can't test this without access to kptr_restrict. */
 }
 
 static void __init

lib/vsprintf.c

···
 #include <linux/uuid.h>
 #include <linux/of.h>
 #include <net/addrconf.h>
+#include <linux/siphash.h>
+#include <linux/compiler.h>
 #ifdef CONFIG_BLOCK
 #include <linux/blkdev.h>
 #endif
···
 	return string(buf, end, uuid, spec);
 }
 
+int kptr_restrict __read_mostly;
+
+static noinline_for_stack
+char *restricted_pointer(char *buf, char *end, const void *ptr,
+			 struct printf_spec spec)
+{
+	spec.base = 16;
+	spec.flags |= SMALL;
+	if (spec.field_width == -1) {
+		spec.field_width = 2 * sizeof(ptr);
+		spec.flags |= ZEROPAD;
+	}
+
+	switch (kptr_restrict) {
+	case 0:
+		/* Always print %pK values */
+		break;
+	case 1: {
+		const struct cred *cred;
+
+		/*
+		 * kptr_restrict==1 cannot be used in IRQ context
+		 * because its test for CAP_SYSLOG would be meaningless.
+		 */
+		if (in_irq() || in_serving_softirq() || in_nmi())
+			return string(buf, end, "pK-error", spec);
+
+		/*
+		 * Only print the real pointer value if the current
+		 * process has CAP_SYSLOG and is running with the
+		 * same credentials it started with. This is because
+		 * access to files is checked at open() time, but %pK
+		 * checks permission at read() time. We don't want to
+		 * leak pointer values if a binary opens a file using
+		 * %pK and then elevates privileges before reading it.
+		 */
+		cred = current_cred();
+		if (!has_capability_noaudit(current, CAP_SYSLOG) ||
+		    !uid_eq(cred->euid, cred->uid) ||
+		    !gid_eq(cred->egid, cred->gid))
+			ptr = NULL;
+		break;
+	}
+	case 2:
+	default:
+		/* Always print 0's for %pK */
+		ptr = NULL;
+		break;
+	}
+
+	return number(buf, end, (unsigned long)ptr, spec);
+}
+
 static noinline_for_stack
 char *netdev_bits(char *buf, char *end, const void *addr, const char *fmt)
 {
···
 	return widen_string(buf, buf - buf_start, end, spec);
 }
 
-int kptr_restrict __read_mostly;
+static noinline_for_stack
+char *pointer_string(char *buf, char *end, const void *ptr,
+		     struct printf_spec spec)
+{
+	spec.base = 16;
+	spec.flags |= SMALL;
+	if (spec.field_width == -1) {
+		spec.field_width = 2 * sizeof(ptr);
+		spec.flags |= ZEROPAD;
+	}
+
+	return number(buf, end, (unsigned long int)ptr, spec);
+}
+
+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
···
  *                        c major compatible string
  *                        C full compatible string
  *
+ * - 'x' For printing the address. Equivalent to "%lx".
+ *
  * ** Please update also Documentation/printk-formats.txt when making changes **
  *
  * Note: The difference between 'S' and 'F' is that on ia64 and ppc64
  * function pointers are really function descriptors, which contain a
  * 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
 char *pointer(const char *fmt, char *buf, char *end, void *ptr,
···
 			return buf;
 		}
 	case 'K':
-		switch (kptr_restrict) {
-		case 0:
-			/* Always print %pK values */
-			break;
-		case 1: {
-			const struct cred *cred;
-
-			/*
-			 * kptr_restrict==1 cannot be used in IRQ context
-			 * because its test for CAP_SYSLOG would be meaningless.
-			 */
-			if (in_irq() || in_serving_softirq() || in_nmi()) {
-				if (spec.field_width == -1)
-					spec.field_width = default_width;
-				return string(buf, end, "pK-error", spec);
-			}
-
-			/*
-			 * Only print the real pointer value if the current
-			 * process has CAP_SYSLOG and is running with the
-			 * same credentials it started with. This is because
-			 * access to files is checked at open() time, but %pK
-			 * checks permission at read() time. We don't want to
-			 * leak pointer values if a binary opens a file using
-			 * %pK and then elevates privileges before reading it.
-			 */
-			cred = current_cred();
-			if (!has_capability_noaudit(current, CAP_SYSLOG) ||
-			    !uid_eq(cred->euid, cred->uid) ||
-			    !gid_eq(cred->egid, cred->gid))
-				ptr = NULL;
-			break;
-		}
-		case 2:
-		default:
-			/* Always print 0's for %pK */
-			ptr = NULL;
-			break;
-		}
-		break;
-
+		return restricted_pointer(buf, end, ptr, spec);
 	case 'N':
 		return netdev_bits(buf, end, ptr, fmt);
 	case 'a':
···
 		case 'F':
 			return device_node_string(buf, end, ptr, spec, fmt + 1);
 		}
+	case 'x':
+		return pointer_string(buf, end, ptr, spec);
 	}
-	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);
 }
 
 /*

mm/kasan/report.c

···
 
 	pr_err("BUG: KASAN: %s in %pS\n",
 		bug_type, (void *)info->ip);
-	pr_err("%s of size %zu at addr %p by task %s/%d\n",
+	pr_err("%s of size %zu at addr %px by task %s/%d\n",
 		info->is_write ? "Write" : "Read", info->access_size,
 		info->access_addr, current->comm, task_pid_nr(current));
 }
···
 	const char *rel_type;
 	int rel_bytes;
 
-	pr_err("The buggy address belongs to the object at %p\n"
+	pr_err("The buggy address belongs to the object at %px\n"
 	       " which belongs to the cache %s of size %d\n",
 		object, cache->name, cache->object_size);
 
···
 	}
 
 	pr_err("The buggy address is located %d bytes %s of\n"
-	       " %d-byte region [%p, %p)\n",
+	       " %d-byte region [%px, %px)\n",
 		rel_bytes, rel_type, cache->object_size, (void *)object_addr,
 		(void *)(object_addr + cache->object_size));
 }
···
 		char shadow_buf[SHADOW_BYTES_PER_ROW];
 
 		snprintf(buffer, sizeof(buffer),
-			(i == 0) ? ">%p: " : " %p: ", kaddr);
+			(i == 0) ? ">%px: " : " %px: ", kaddr);
 		/*
 		 * We should not pass a shadow pointer to generic
 		 * function, because generic functions may try to

scripts/checkpatch.pl

···
 		        for (my $count = $linenr; $count <= $lc; $count++) {
 				my $fmt = get_quoted_string($lines[$count - 1], raw_line($count, 0));
 				$fmt =~ s/%%//g;
-				if ($fmt =~ /(\%[\*\d\.]*p(?![\WFfSsBKRraEhMmIiUDdgVCbGNO]).)/) {
+				if ($fmt =~ /(\%[\*\d\.]*p(?![\WFfSsBKRraEhMmIiUDdgVCbGNOx]).)/) {
 					$bad_extension = $1;
 					last;
 				}