Commit 1853db0e authored Aug 10, 2009 by Frederic Weisbecker Committed by Ingo Molnar Aug 10, 2009

perf_counter: Zero dead bytes from ftrace raw samples size alignment



After aligning the ftrace raw samples, there are dead bytes storing
random data from the stack. We don't want to leak these to userspace,
then zero these out.

Before:

	0x2de88 [0x50]: event: 9
	.
	. ... raw event: size 80 bytes
	.  0000:  09 00 00 00 01 00 50 00 d0 c7 00 81 ff ff ff ff  ......P........
	.  0010:  68 01 00 00 68 01 00 00 2c 00 00 00 00 00 00 00  h...h...,......
	.  0020:  2c 00 00 00 2b 00 01 02 68 01 00 00 68 01 00 00  ,...+...h...h..
	.  0030:  6b 6f 6e 64 65 6d 61 6e 64 2f 30 00 00 00 00 00  kondemand/0....
	.  0040:  68 01 00 00 40 7f 46 81 ff ff ff ff 00 10 1b 7f  h...@.F........
                                                      ^  ^  ^  ^
                                                         Leak

After:

	0x2d318 [0x50]: event: 9
	.
	. ... raw event: size 80 bytes
	.  0000:  09 00 00 00 01 00 50 00 d0 c7 00 81 ff ff ff ff  ......P........
	.  0010:  68 01 00 00 68 01 00 00 68 14 00 00 00 00 00 00  h...h...h......
	.  0020:  2c 00 00 00 2b 00 01 02 68 01 00 00 68 01 00 00  ,...+...h...h..
	.  0030:  6b 6f 6e 64 65 6d 61 6e 64 2f 30 00 00 00 00 00  kondemand/0....
	.  0040:  68 01 00 00 a0 80 46 81 ff ff ff ff 00 00 00 00  h.....F........
                                                      ^  ^  ^  ^
							 Fixed

Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
LKML-Reference: <1249915116-5210-1-git-send-email-fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>

parent 304703ab

include/trace/ftrace.h

+4 −0

Original line number	Diff line number	Diff line
		@@ -648,6 +648,9 @@ __attribute__((section("_ftrace_events"))) event_##call = { \
		* char raw_data[__entry_size]; <- allocate our sample in the stack
		* struct trace_entry *ent;
		*
		* zero dead bytes from alignment to avoid stack leak to userspace:
		*
		* (u64 )(&raw_data[__entry_size - sizeof(u64)]) = 0ULL;
		* entry = (struct ftrace_raw_<call> *)raw_data;
		* ent = &entry->ent;
		* tracing_generic_entry_update(ent, irq_flags, pc);
		@@ -698,6 +701,7 @@ static void ftrace_profile_##call(proto) \
		char raw_data[__entry_size]; \
		struct trace_entry *ent; \
		\
		(u64 )(&raw_data[__entry_size - sizeof(u64)]) = 0ULL; \
		entry = (struct ftrace_raw_##call *)raw_data; \
		ent = &entry->ent; \
		tracing_generic_entry_update(ent, irq_flags, pc); \

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