linux-kernel - [PATCH v4 3/4] printk/nmi: Warn when some message has been lost in NMI context

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <1449840052-10491-4-git-send-email-pmladek@suse.com>
Date:	Fri, 11 Dec 2015 14:20:51 +0100
From:	Petr Mladek <pmladek@...e.com>
To:	akpm@...ux-foundation.org
Cc:	linux-kernel@...r.kernel.org,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Arnd Bergmann <arnd@...db.de>, jkosina@...e.com,
	pmladek@...e.com
Subject: [PATCH v4 3/4] printk/nmi: Warn when some message has been lost in NMI context

We could not resize the temporary buffer in NMI context. Let's warn
if a message is lost.

This is rather theoretical. printk() should not be used in NMI.
The only sensible use is when we want to print backtrace from all
CPUs. The current buffer should be enough for this purpose.

Signed-off-by: Petr Mladek <pmladek@...e.com>
Cc: Jan Kara <jack@...e.cz>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Russell King <rmk+kernel@....linux.org.uk>
Cc: Daniel Thompson <daniel.thompson@...aro.org>
Cc: Jiri Kosina <jkosina@...e.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ralf Baechle <ralf@...ux-mips.org>
Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc: Martin Schwidefsky <schwidefsky@...ibm.com>
Cc: David Miller <davem@...emloft.net>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---
 kernel/printk/internal.h | 11 +++++++++++
 kernel/printk/nmi.c      |  5 ++++-
 kernel/printk/printk.c   | 10 ++++++++++
 3 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h
index 2de99faedfc1..341bedccc065 100644
--- a/kernel/printk/internal.h
+++ b/kernel/printk/internal.h
@@ -34,6 +34,12 @@ static inline __printf(1, 0) int vprintk_func(const char *fmt, va_list args)
 	return this_cpu_read(printk_func)(fmt, args);
 }
 
+extern atomic_t nmi_message_lost;
+static inline int get_nmi_message_lost(void)
+{
+	return atomic_xchg(&nmi_message_lost, 0);
+}
+
 #else /* CONFIG_PRINTK_NMI */
 
 static inline __printf(1, 0) int vprintk_func(const char *fmt, va_list args)
@@ -41,4 +47,9 @@ static inline __printf(1, 0) int vprintk_func(const char *fmt, va_list args)
 	return vprintk_default(fmt, args);
 }
 
+static inline int get_nmi_message_lost(void)
+{
+	return 0;
+}
+
 #endif /* CONFIG_PRINTK_NMI */
diff --git a/kernel/printk/nmi.c b/kernel/printk/nmi.c
index 9a506bd18b9d..d86f55cccf31 100644
--- a/kernel/printk/nmi.c
+++ b/kernel/printk/nmi.c
@@ -39,6 +39,7 @@
  */
 DEFINE_PER_CPU(printk_func_t, printk_func) = vprintk_default;
 static int printk_nmi_irq_ready;
+atomic_t nmi_message_lost;
 
 #define NMI_LOG_BUF_LEN (4096 - sizeof(atomic_t) - sizeof(struct irq_work))
 
@@ -64,8 +65,10 @@ static int vprintk_nmi(const char *fmt, va_list args)
 again:
 	len = atomic_read(&s->len);
 
-	if (len >= sizeof(s->buffer))
+	if (len >= sizeof(s->buffer)) {
+		atomic_inc(&nmi_message_lost);
 		return 0;
+	}
 
 	/*
 	 * Make sure that all old data have been read before the buffer was
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 480ad05ab299..71183a308b9e 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1669,6 +1669,7 @@ asmlinkage int vprintk_emit(int facility, int level,
 	unsigned long flags;
 	int this_cpu;
 	int printed_len = 0;
+	int nmi_message_lost;
 	bool in_sched = false;
 	/* cpu currently holding logbuf_lock in this function */
 	static unsigned int logbuf_cpu = UINT_MAX;
@@ -1719,6 +1720,15 @@ asmlinkage int vprintk_emit(int facility, int level,
 					 strlen(recursion_msg));
 	}
 
+	nmi_message_lost = get_nmi_message_lost();
+	if (unlikely(nmi_message_lost)) {
+		text_len = scnprintf(textbuf, sizeof(textbuf),
+				     "BAD LUCK: lost %d message(s) from NMI context!",
+				     nmi_message_lost);
+		printed_len += log_store(0, 2, LOG_PREFIX|LOG_NEWLINE, 0,
+					 NULL, 0, textbuf, text_len);
+	}
+
 	/*
 	 * The printf needs to come first; we need the syslog
 	 * prefix which might be passed-in as a parameter.
-- 
1.8.5.6

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/