Merge tag 'printk-for-5.12' of git://git.kernel.org/pub/scm/linux/kernel/git/printk...

Pull printk updates from Petr Mladek:

 - New "no_hash_pointers" kernel parameter causes that %p shows raw
   pointer values instead of hashed ones. It is intended only for
   debugging purposes. Misuse is prevented by a fat warning message that
   is inspired by trace_printk().

 - Prevent a possible deadlock when flushing printk_safe buffers during
   panic().

 - Fix performance regression caused by the lockless printk ringbuffer.
   It was visible with huge log buffer and long messages.

 - Documentation fix-up.

* tag 'printk-for-5.12' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux:
  lib/vsprintf: no_hash_pointers prints all addresses as unhashed
  kselftest: add support for skipped tests
  lib: use KSTM_MODULE_GLOBALS macro in kselftest drivers
  printk: avoid prb_first_valid_seq() where possible
  printk: fix deadlock when kernel panic
  printk: rectify kernel-doc for prb_rec_init_wr()

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 52f8233..8b5f717 100644 (file)
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3293,6 +3293,21 @@
                        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/kernel/printk/printk.c b/kernel/printk/printk.c
index 5a95c68..575a34b 100644 (file)
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -735,9 +735,9 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
                logbuf_lock_irq();
        }
 
-       if (user->seq < prb_first_valid_seq(prb)) {
+       if (r->info->seq != user->seq) {
                /* our last seen message is gone, return error and reset */
-               user->seq = prb_first_valid_seq(prb);
+               user->seq = r->info->seq;
                ret = -EPIPE;
                logbuf_unlock_irq();
                goto out;
@@ -812,6 +812,7 @@ static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
 static __poll_t devkmsg_poll(struct file *file, poll_table *wait)
 {
        struct devkmsg_user *user = file->private_data;
+       struct printk_info info;
        __poll_t ret = 0;
 
        if (!user)
@@ -820,9 +821,9 @@ static __poll_t devkmsg_poll(struct file *file, poll_table *wait)
        poll_wait(file, &log_wait, wait);
 
        logbuf_lock_irq();
-       if (prb_read_valid(prb, user->seq, NULL)) {
+       if (prb_read_valid_info(prb, user->seq, &info, NULL)) {
                /* return error when data has vanished underneath us */
-               if (user->seq < prb_first_valid_seq(prb))
+               if (info.seq != user->seq)
                        ret = EPOLLIN|EPOLLRDNORM|EPOLLERR|EPOLLPRI;
                else
                        ret = EPOLLIN|EPOLLRDNORM;
@@ -1559,6 +1560,7 @@ static void syslog_clear(void)
 
 int do_syslog(int type, char __user *buf, int len, int source)
 {
+       struct printk_info info;
        bool clear = false;
        static int saved_console_loglevel = LOGLEVEL_DEFAULT;
        int error;
@@ -1629,9 +1631,14 @@ int do_syslog(int type, char __user *buf, int len, int source)
        /* Number of chars in the log buffer */
        case SYSLOG_ACTION_SIZE_UNREAD:
                logbuf_lock_irq();
-               if (syslog_seq < prb_first_valid_seq(prb)) {
+               if (!prb_read_valid_info(prb, syslog_seq, &info, NULL)) {
+                       /* No unread messages. */
+                       logbuf_unlock_irq();
+                       return 0;
+               }
+               if (info.seq != syslog_seq) {
                        /* messages are gone, move to first one */
-                       syslog_seq = prb_first_valid_seq(prb);
+                       syslog_seq = info.seq;
                        syslog_partial = 0;
                }
                if (source == SYSLOG_FROM_PROC) {
@@ -1643,7 +1650,6 @@ int do_syslog(int type, char __user *buf, int len, int source)
                        error = prb_next_seq(prb) - syslog_seq;
                } else {
                        bool time = syslog_partial ? syslog_time : printk_time;
-                       struct printk_info info;
                        unsigned int line_count;
                        u64 seq;
 
@@ -3429,9 +3435,11 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
                goto out;
 
        logbuf_lock_irqsave(flags);
-       if (dumper->cur_seq < prb_first_valid_seq(prb)) {
-               /* messages are gone, move to first available one */
-               dumper->cur_seq = prb_first_valid_seq(prb);
+       if (prb_read_valid_info(prb, dumper->cur_seq, &info, NULL)) {
+               if (info.seq != dumper->cur_seq) {
+                       /* messages are gone, move to first available one */
+                       dumper->cur_seq = info.seq;
+               }
        }
 
        /* last entry */

diff --git a/kernel/printk/printk_ringbuffer.h b/kernel/printk/printk_ringbuffer.h
index 5dc9d02..73cc80e 100644 (file)
--- a/kernel/printk/printk_ringbuffer.h
+++ b/kernel/printk/printk_ringbuffer.h
@@ -287,7 +287,7 @@ _DEFINE_PRINTKRB(name, descbits, avgtextbits, &_##name##_text[0])
 /* Writer Interface */
 
 /**
- * prb_rec_init_wd() - Initialize a buffer for writing records.
+ * prb_rec_init_wr() - Initialize a buffer for writing records.
  *
  * @r:             The record to initialize.
  * @text_buf_size: The needed text buffer size.

diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c
index a0e6f74..2e9e3ed 100644 (file)
--- a/kernel/printk/printk_safe.c
+++ b/kernel/printk/printk_safe.c
@@ -45,6 +45,8 @@ struct printk_safe_seq_buf {
 static DEFINE_PER_CPU(struct printk_safe_seq_buf, safe_print_seq);
 static DEFINE_PER_CPU(int, printk_context);
 
+static DEFINE_RAW_SPINLOCK(safe_read_lock);
+
 #ifdef CONFIG_PRINTK_NMI
 static DEFINE_PER_CPU(struct printk_safe_seq_buf, nmi_print_seq);
 #endif
@@ -180,8 +182,6 @@ static void report_message_lost(struct printk_safe_seq_buf *s)
  */
 static void __printk_safe_flush(struct irq_work *work)
 {
-       static raw_spinlock_t read_lock =
-               __RAW_SPIN_LOCK_INITIALIZER(read_lock);
        struct printk_safe_seq_buf *s =
                container_of(work, struct printk_safe_seq_buf, work);
        unsigned long flags;
@@ -195,7 +195,7 @@ static void __printk_safe_flush(struct irq_work *work)
         * different CPUs. This is especially important when printing
         * a backtrace.
         */
-       raw_spin_lock_irqsave(&read_lock, flags);
+       raw_spin_lock_irqsave(&safe_read_lock, flags);
 
        i = 0;
 more:
@@ -232,7 +232,7 @@ more:
 
 out:
        report_message_lost(s);
-       raw_spin_unlock_irqrestore(&read_lock, flags);
+       raw_spin_unlock_irqrestore(&safe_read_lock, flags);
 }
 
 /**
@@ -278,6 +278,14 @@ void printk_safe_flush_on_panic(void)
                raw_spin_lock_init(&logbuf_lock);
        }
 
+       if (raw_spin_is_locked(&safe_read_lock)) {
+               if (num_online_cpus() > 1)
+                       return;
+
+               debug_locks_off();
+               raw_spin_lock_init(&safe_read_lock);
+       }
+
        printk_safe_flush();
 }
 

diff --git a/lib/test_bitmap.c b/lib/test_bitmap.c
index 4425a1d..0ea0e82 100644 (file)
--- a/lib/test_bitmap.c
+++ b/lib/test_bitmap.c
@@ -16,8 +16,7 @@
 
 #include "../tools/testing/selftests/kselftest_module.h"
 
-static unsigned total_tests __initdata;
-static unsigned failed_tests __initdata;
+KSTM_MODULE_GLOBALS();
 
 static char pbl_buffer[PAGE_SIZE] __initdata;
 

diff --git a/lib/test_printf.c b/lib/test_printf.c
index 7d60f24..95a2f82 100644 (file)
--- a/lib/test_printf.c
+++ b/lib/test_printf.c
@@ -30,11 +30,13 @@
 #define PAD_SIZE 16
 #define FILL_CHAR '$'
 
-static unsigned total_tests __initdata;
-static unsigned failed_tests __initdata;
+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)
@@ -301,6 +303,12 @@ 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 3b53c73..41ddc35 100644 (file)
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -2090,6 +2090,32 @@ char *fwnode_string(char *buf, char *end, struct fwnode_handle *fwnode,
        return widen_string(buf, buf - buf_start, end, 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
@@ -2297,8 +2323,14 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
                }
        }
 
-       /* 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);
 }
 
 /*

diff --git a/tools/testing/selftests/kselftest_module.h b/tools/testing/selftests/kselftest_module.h
index e8eafaf..e2ea41d 100644 (file)
--- a/tools/testing/selftests/kselftest_module.h
+++ b/tools/testing/selftests/kselftest_module.h
@@ -11,7 +11,8 @@
 
 #define KSTM_MODULE_GLOBALS()                  \
 static unsigned int total_tests __initdata;    \
-static unsigned int failed_tests __initdata
+static unsigned int failed_tests __initdata;   \
+static unsigned int skipped_tests __initdata
 
 #define KSTM_CHECK_ZERO(x) do {                                                \
        total_tests++;                                                  \
@@ -21,11 +22,16 @@ static unsigned int failed_tests __initdata
        }                                                               \
 } while (0)
 
-static inline int kstm_report(unsigned int total_tests, unsigned int failed_tests)
+static inline int kstm_report(unsigned int total_tests, unsigned int failed_tests,
+                             unsigned int skipped_tests)
 {
-       if (failed_tests == 0)
-               pr_info("all %u tests passed\n", total_tests);
-       else
+       if (failed_tests == 0) {
+               if (skipped_tests) {
+                       pr_info("skipped %u tests\n", skipped_tests);
+                       pr_info("remaining %u tests passed\n", total_tests);
+               } else
+                       pr_info("all %u tests passed\n", total_tests);
+       } else
                pr_warn("failed %u out of %u tests\n", failed_tests, total_tests);
 
        return failed_tests ? -EINVAL : 0;
@@ -36,7 +42,7 @@ static int __init __module##_init(void)                       \
 {                                                      \
        pr_info("loaded.\n");                           \
        selftest();                                     \
-       return kstm_report(total_tests, failed_tests);  \
+       return kstm_report(total_tests, failed_tests, skipped_tests);   \
 }                                                      \
 static void __exit __module##_exit(void)               \
 {                                                      \