linux-kernel - [PATCH 3/4] nmi_backtrace: do a local dump

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: <1456782024-7122-4-git-send-email-cmetcalf@ezchip.com>
Date:	Mon, 29 Feb 2016 16:40:23 -0500
From:	Chris Metcalf <cmetcalf@...hip.com>
To:	Russell King <linux@....linux.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	Aaron Tomlin <atomlin@...hat.com>,
	Ingo Molnar <mingo@...hat.com>, Andrew Morton <akpm@...l.org>,
	Daniel Thompson <daniel.thompson@...aro.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>
CC:	Chris Metcalf <cmetcalf@...hip.com>
Subject: [PATCH 3/4] nmi_backtrace: do a local dump_stack() instead of a self-NMI

Currently on arm there is code that checks whether it should call
dump_stack() explicitly, to avoid trying to raise an NMI when the
current context is not preemptible by the backtrace IPI.  Similarly,
the forthcoming arch/tile support uses an IPI mechanism that does
not support generating an NMI to self.

Accordingly, move the code that guards this case into the generic
mechanism, and invoke it unconditionally whenever we want a
backtrace of the current cpu.  It seems plausible that in all cases,
dump_stack() will generate better information than generating a
stack from the NMI handler.  The register state will be missing,
but that state is likely not particularly helpful in any case.

Or, if we think it is helpful, we should be capturing and emitting
the current register state in all cases when regs == NULL is passed
to nmi_cpu_backtrace().

Signed-off-by: Chris Metcalf <cmetcalf@...hip.com>
---
 arch/arm/kernel/smp.c | 9 ---------
 lib/nmi_backtrace.c   | 9 +++++++++
 2 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index 208125658e56..26a9ac6bc616 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -746,15 +746,6 @@ core_initcall(register_cpufreq_notifier);
 
 static void raise_nmi(cpumask_t *mask)
 {
-	/*
-	 * Generate the backtrace directly if we are running in a calling
-	 * context that is not preemptible by the backtrace IPI. Note
-	 * that nmi_cpu_backtrace() automatically removes the current cpu
-	 * from mask.
-	 */
-	if (cpumask_test_cpu(smp_processor_id(), mask) && irqs_disabled())
-		nmi_cpu_backtrace(NULL);
-
 	smp_cross_call(mask, IPI_CPU_BACKTRACE);
 }
 
diff --git a/lib/nmi_backtrace.c b/lib/nmi_backtrace.c
index f878efc9e851..b9a92b90b914 100644
--- a/lib/nmi_backtrace.c
+++ b/lib/nmi_backtrace.c
@@ -76,6 +76,15 @@ void nmi_trigger_cpumask_backtrace(const cpumask_t *mask,
 		seq_buf_init(&s->seq, s->buffer, NMI_BUF_SIZE);
 	}
 
+	/*
+	 * Don't try to send an NMI to this cpu; it may work on some
+	 * architectures, but on others it may not, and we'll get
+	 * information at least as useful just by doing a dump_stack() here.
+	 * Note that nmi_cpu_backtrace(NULL) will clear the cpu bit.
+	 */
+	if (cpumask_test_cpu(this_cpu, to_cpumask(backtrace_mask)))
+		nmi_cpu_backtrace(NULL);
+
 	if (!cpumask_empty(to_cpumask(backtrace_mask))) {
 		pr_info("Sending NMI from CPU %d to CPUs %*pbl:\n",
 			this_cpu, nr_cpumask_bits, to_cpumask(backtrace_mask));
-- 
2.1.2