Messages in this thread Patch in this message | | | Date | Fri, 2 Apr 2021 09:33:15 -0400 | From | Steven Rostedt <> | Subject | [GIT PULL] tracing: Fix stack trace event size |
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Linus,
Fix stack trace entry size to stop showing garbage
The macro that creates both the structure and the format displayed to user space for the stack trace event was changed a while ago to fix the parsing by user space tooling. But this change also modified the structure used to store the stack trace event. It changed the caller array field from [0] to [8]. Even though the size in the ring buffer is dynamic and can be something other than 8 (user space knows how to handle this), the 8 extra words was not accounted for when reserving the event on the ring buffer, and added 8 more entries, due to the calculation of "sizeof(*entry) + nr_entries * sizeof(long)", as the sizeof(*entry) now contains 8 entries. The size of the caller field needs to be subtracted from the size of the entry to create the correct allocation size.
Please pull the latest trace-v5.12-rc5-2 tree, which can be found at:
git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git trace-v5.12-rc5-2
Tag SHA1: cb39aeb904fb1dc0fff7e13799d9ad287fb4697f Head SHA1: 9deb193af69d3fd6dd8e47f292b67c805a787010
Steven Rostedt (VMware) (1): tracing: Fix stack trace event size
---- kernel/trace/trace.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --------------------------- commit 9deb193af69d3fd6dd8e47f292b67c805a787010 Author: Steven Rostedt (VMware) <rostedt@goodmis.org> Date: Thu Apr 1 13:54:40 2021 -0400
tracing: Fix stack trace event size Commit cbc3b92ce037 fixed an issue to modify the macros of the stack trace event so that user space could parse it properly. Originally the stack trace format to user space showed that the called stack was a dynamic array. But it is not actually a dynamic array, in the way that other dynamic event arrays worked, and this broke user space parsing for it. The update was to make the array look to have 8 entries in it. Helper functions were added to make it parse it correctly, as the stack was dynamic, but was determined by the size of the event stored. Although this fixed user space on how it read the event, it changed the internal structure used for the stack trace event. It changed the array size from [0] to [8] (added 8 entries). This increased the size of the stack trace event by 8 words. The size reserved on the ring buffer was the size of the stack trace event plus the number of stack entries found in the stack trace. That commit caused the amount to be 8 more than what was needed because it did not expect the caller field to have any size. This produced 8 entries of garbage (and reading random data) from the stack trace event: <idle>-0 [002] d... 1976396.837549: <stack trace> => trace_event_raw_event_sched_switch => __traceiter_sched_switch => __schedule => schedule_idle => do_idle => cpu_startup_entry => secondary_startup_64_no_verify => 0xc8c5e150ffff93de => 0xffff93de => 0 => 0 => 0xc8c5e17800000000 => 0x1f30affff93de => 0x00000004 => 0x200000000 Instead, subtract the size of the caller field from the size of the event to make sure that only the amount needed to store the stack trace is reserved. Link: https://lore.kernel.org/lkml/your-ad-here.call-01617191565-ext-9692@work.hours/ Cc: stable@vger.kernel.org Fixes: cbc3b92ce037 ("tracing: Set kernel_stack's caller size properly") Reported-by: Vasily Gorbik <gor@linux.ibm.com> Tested-by: Vasily Gorbik <gor@linux.ibm.com> Acked-by: Vasily Gorbik <gor@linux.ibm.com> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index eccb4e1187cc..5c777627212f 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -2984,7 +2984,8 @@ static void __ftrace_trace_stack(struct trace_buffer *buffer, size = nr_entries * sizeof(unsigned long); event = __trace_buffer_lock_reserve(buffer, TRACE_STACK, - sizeof(*entry) + size, trace_ctx); + (sizeof(*entry) - sizeof(entry->caller)) + size, + trace_ctx); if (!event) goto out; entry = ring_buffer_event_data(event);
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