lib/vsprintf: Less restrictive hashed pointer printing

Commit ad67b74d24 ("printk: hash addresses printed with %p") and
Commit ef0010a309 ("vsprintf: don't use 'restricted_pointer()'
when not restricting") effectively removed the ability to display
kernel addresses in the kernel log. While this may be a useful feature
in production builds, it is undesirable when trying to debug.

%px is not a possible alternative, because it is unable to differentiate
between a debug and production build.

Change-Id: I139fae7b8488936d214efdd2b5b807fa1c005467
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>

lib/Kconfig.debug

@@ -146,6 +146,15 @@ config DYNAMIC_DEBUG
 	  See Documentation/admin-guide/dynamic-debug-howto.rst for additional
 	  information.
 
+config DEBUG_CONSOLE_UNHASHED_POINTERS
+	bool "Display unhashed kernel pointers"
+	depends on DEBUG_KERNEL
+	help
+	  Pointers %p and %pK are normally hashed prior to being displayed to
+	  prevent leaking kernel addresses. On debug builds, always print
+	  actual pointer values, ignoring the kptr_restrict setting.
+	  Not to be enabled on production builds.
+
 endmenu # "printk and dmesg options"
 
 menu "Compile-time checks and compiler options"

lib/vsprintf.c

@@ -1940,7 +1940,8 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
 			return buf;
 		}
 	case 'K':
-		if (!kptr_restrict)
+		if (!kptr_restrict ||
+		    IS_ENABLED(CONFIG_DEBUG_CONSOLE_UNHASHED_POINTERS))
 			break;
 		return restricted_pointer(buf, end, ptr, spec);
 	case 'N':
@@ -1972,6 +1973,9 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
 		return pointer_string(buf, end, ptr, spec);
 	}
 
+	if (IS_ENABLED(CONFIG_DEBUG_CONSOLE_UNHASHED_POINTERS))
+		return pointer_string(buf, end, ptr, spec);
+
 	/* default is to _not_ leak addresses, hash before printing */
 	return ptr_to_id(buf, end, ptr, spec);
 }