From: "Steven Rostedt (VMware)" rostedt@goodmis.org

commit 9deb193af69d3fd6dd8e47f292b67c805a787010 upstream.

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.hou...

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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/trace/trace.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 2780a98682078..032e62c42a5c2 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -2645,7 +2645,8 @@ static void __ftrace_trace_stack(struct ring_buffer *buffer, size *= sizeof(unsigned long);

event = __trace_buffer_lock_reserve(buffer, TRACE_STACK, - sizeof(*entry) + size, flags, pc); + (sizeof(*entry) - sizeof(entry->caller)) + size, + flags, pc); if (!event) goto out; entry = ring_buffer_event_data(event);