[PATCH 3/5] vsprintf: add specifier %px, unique identifier

@@ -462,10 +462,84 @@ flags(void)
 	kfree(cmp_buffer);
 }
 
+#define HASHED_BUF_SIZE 64	/* leave some space so we don't oops */
+
+#if BITS_PER_LONG == 64
+
+#define PTR ((void *)0xffff0123456789ab)
+#define PTR_STR "ffff0123456789ab"
+#define ZEROS "00000000"	/* hex 32 zero bits */
+
+static int __init
+hashed_format(void)
+{
+	char buf[HASHED_BUF_SIZE];
+	int nchars;
+
+	nchars = snprintf(buf, HASHED_BUF_SIZE, "%px", PTR);
+
+	if (nchars != PTR_WIDTH || strncmp(buf, ZEROS, strlen(ZEROS)) != 0)
+		return -1;
+
+	return 0;
+}
+
+#else
+
+#define PTR ((void *)0x456789ab)
+#define PTR_STR "456789ab"
+
+static int __init
+hashed_format(void)
+{
+	/* Format is implicitly tested for 32 bit machines by hashed_hash() */
+	return 0;
+}
+
+#endif	/* BITS_PER_LONG == 64 */
+
+static int __init
+hashed_hash(void)
+{
+	char buf[HASHED_BUF_SIZE];
+	int nchars;
+
+	nchars = snprintf(buf, HASHED_BUF_SIZE, "%px", PTR);
+
+	if (nchars != PTR_WIDTH || strncmp(buf, PTR_STR, PTR_WIDTH) == 0)
+		return -1;
+
+	return 0;
+}
+
+/*
+ * We can't use test() to test %px because we don't know what output to expect
+ * after an address is hashed.
+ */
+static void __init
+hashed(void)
+{
+	int err;
+
+	err = hashed_hash();
+	if (err) {
+		pr_warn("specifier px does not appear to be hashed\n");
+		failed_tests++;
+		return;
+	}
+
+	err = hashed_format();
+	if (err) {
+		pr_warn("hashed output from px has unexpected format\n");
+		failed_tests++;
+	}
+}
+
 static void __init
 test_pointer(void)
 {
 	plain();
+	hashed();
 	symbol_ptr();
 	kernel_ptr();
 	struct_resource();

@@ -33,6 +33,8 @@
 #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

@@ -1644,6 +1646,73 @@ char *device_node_string(char *buf, char *end, struct device_node *dn,
 	return widen_string(buf, buf - buf_start, end, 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
  * by an extra set of alphanumeric characters that are extended format

@@ -1868,6 +1937,8 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
 		case 'F':
 			return device_node_string(buf, end, ptr, spec, fmt + 1);
 		}
+	case 'x':
+		return ptr_to_id(buf, end, ptr, spec);
 	}
 	spec.flags |= SMALL;
 	if (spec.field_width == -1) {

@@ -5753,7 +5753,7 @@ sub process {
 		        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;
 				}