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authorSteven Rostedt (VMware) <rostedt@goodmis.org>2017-09-05 11:32:01 -0400
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2017-09-27 14:39:23 +0200
commit96cf918df428c16986cf88b3ebac465e04c3f5f6 (patch)
tree5c675c72bfcc783fcfc35ade06e91f1ee364c633 /kernel/trace
parent100553e197e2c41eccf9fa04b2be9cd11ae21215 (diff)
tracing: Add barrier to trace_printk() buffer nesting modification
commit 3d9622c12c8873911f4cc0ccdabd0362c2fca06b upstream. trace_printk() uses 4 buffers, one for each context (normal, softirq, irq and NMI), such that it does not need to worry about one context preempting the other. There's a nesting counter that gets incremented to figure out which buffer to use. If the context gets preempted by another context which calls trace_printk() it will increment the counter and use the next buffer, and restore the counter when it is finished. The problem is that gcc may optimize the modification of the buffer nesting counter and it may not be incremented in memory before the buffer is used. If this happens, and the context gets interrupted by another context, it could pick the same buffer and corrupt the one that is being used. Compiler barriers need to be added after the nesting variable is incremented and before it is decremented to prevent usage of the context buffers by more than one context at the same time. Cc: Andy Lutomirski <luto@kernel.org> Fixes: e2ace00117 ("tracing: Choose static tp_printk buffer by explicit nesting count") Hat-tip-to: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'kernel/trace')
-rw-r--r--kernel/trace/trace.c8
1 files changed, 7 insertions, 1 deletions
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 7379f735a9f4..2508c319ae5f 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2369,11 +2369,17 @@ static char *get_trace_buf(void)
if (!buffer || buffer->nesting >= 4)
return NULL;
- return &buffer->buffer[buffer->nesting++][0];
+ buffer->nesting++;
+
+ /* Interrupts must see nesting incremented before we use the buffer */
+ barrier();
+ return &buffer->buffer[buffer->nesting][0];
}
static void put_trace_buf(void)
{
+ /* Don't let the decrement of nesting leak before this */
+ barrier();
this_cpu_dec(trace_percpu_buffer->nesting);
}