From b25c7b6b0f9535a9313e0ba998dba335fa7b930f Mon Sep 17 00:00:00 2001 From: Timur Tabi Date: Sun, 14 Feb 2021 10:13:48 -0600 Subject: [PATCH] UPSTREAM: lib/vsprintf: no_hash_pointers prints all addresses as unhashed If the no_hash_pointers command line parameter is set, then printk("%p") will print pointers as unhashed, which is useful for debugging purposes. This change applies to any function that uses vsprintf, such as print_hex_dump() and seq_buf_printf(). A large warning message is displayed if this option is enabled. Unhashed pointers expose kernel addresses, which can be a security risk. Also update test_printf to skip the hashed pointer tests if the command-line option is set. Signed-off-by: Timur Tabi Acked-by: Petr Mladek Acked-by: Randy Dunlap Acked-by: Sergey Senozhatsky Acked-by: Vlastimil Babka Acked-by: Marco Elver Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20210214161348.369023-4-timur@kernel.org Bug: 177201466 Bug: 180086542 (cherry picked from commit 5ead723a20e0447bc7db33dc3070b420e5f80aa6) Signed-off-by: Alexander Potapenko Change-Id: I9680bb5e076da9f766a66e6076e5c39291188e40 --- .../admin-guide/kernel-parameters.txt | 15 ++++++++ lib/test_printf.c | 8 +++++ lib/vsprintf.c | 36 +++++++++++++++++-- 3 files changed, 57 insertions(+), 2 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 25443c227e27..c33eb805ec85 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -3187,6 +3187,21 @@ in certain environments such as networked servers or real-time systems. + no_hash_pointers + Force pointers printed to the console or buffers to be + unhashed. By default, when a pointer is printed via %p + format string, that pointer is "hashed", i.e. obscured + by hashing the pointer value. This is a security feature + that hides actual kernel addresses from unprivileged + users, but it also makes debugging the kernel more + difficult since unequal pointers can no longer be + compared. However, if this command-line option is + specified, then all normal pointers will have their true + value printed. Pointers printed via %pK may still be + hashed. This option should only be specified when + debugging the kernel. Please do not use on production + kernels. + nohibernate [HIBERNATION] Disable hibernation and resume. nohz= [KNL] Boottime enable/disable dynamic ticks diff --git a/lib/test_printf.c b/lib/test_printf.c index 0f28f7a00684..0a3153f162c7 100644 --- a/lib/test_printf.c +++ b/lib/test_printf.c @@ -33,6 +33,8 @@ KSTM_MODULE_GLOBALS(); static char *test_buffer __initdata; static char *alloced_buffer __initdata; +extern bool no_hash_pointers; + static int __printf(4, 0) __init do_test(int bufsize, const char *expect, int elen, const char *fmt, va_list ap) @@ -299,6 +301,12 @@ plain(void) { int err; + if (no_hash_pointers) { + pr_warn("skipping plain 'p' tests"); + skipped_tests += 2; + return; + } + err = plain_hash(); if (err) { pr_warn("plain 'p' does not appear to be hashed\n"); diff --git a/lib/vsprintf.c b/lib/vsprintf.c index d377456b8c39..f3d84136199b 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -2057,6 +2057,32 @@ static char *kobject_string(char *buf, char *end, void *ptr, return error_string(buf, end, "(%pO?)", spec); } +/* Disable pointer hashing if requested */ +bool no_hash_pointers __ro_after_init; +EXPORT_SYMBOL_GPL(no_hash_pointers); + +static int __init no_hash_pointers_enable(char *str) +{ + no_hash_pointers = true; + + pr_warn("**********************************************************\n"); + pr_warn("** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **\n"); + pr_warn("** **\n"); + pr_warn("** This system shows unhashed kernel memory addresses **\n"); + pr_warn("** via the console, logs, and other interfaces. This **\n"); + pr_warn("** might reduce the security of your system. **\n"); + pr_warn("** **\n"); + pr_warn("** If you see this message and you are not debugging **\n"); + pr_warn("** the kernel, report this immediately to your system **\n"); + pr_warn("** administrator! **\n"); + pr_warn("** **\n"); + pr_warn("** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **\n"); + pr_warn("**********************************************************\n"); + + return 0; +} +early_param("no_hash_pointers", no_hash_pointers_enable); + /* * Show a '%p' thing. A kernel extension is that the '%p' is followed * by an extra set of alphanumeric characters that are extended format @@ -2259,8 +2285,14 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr, 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); + /* + * default is to _not_ leak addresses, so hash before printing, + * unless no_hash_pointers is specified on the command line. + */ + if (unlikely(no_hash_pointers)) + return pointer_string(buf, end, ptr, spec); + else + return ptr_to_id(buf, end, ptr, spec); } /*