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printk changes for 5.12

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

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()
This commit is contained in:
Linus Torvalds 2021-02-22 11:04:36 -08:00
commit b2bec7d8a4
8 changed files with 103 additions and 27 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

15
Documentation/admin-guide/kernel-parameters.txt
View File

@ -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

28
kernel/printk/printk.c
View File

@ -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 */

2
kernel/printk/printk_ringbuffer.h
View File

@ -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.

16
kernel/printk/printk_safe.c
View File

@ -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();
}

3
lib/test_bitmap.c
View File

@ -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;

12
lib/test_printf.c
View File

@ -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");

36
lib/vsprintf.c
View File

@ -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);
}
/*

18
tools/testing/selftests/kselftest_module.h
View File

@ -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) \
{ \