Description
In the Linux kernel, the following vulnerability has been resolved:
tracing: Make sure trace_printk() can output as soon as it can be used
Currently trace_printk() can be used as soon as early_trace_init() is
called from start_kernel(). But if a crash happens, and
"ftrace_dump_on_oops" is set on the kernel command line, all you get will
be:
[ 0.456075] -0 0dN.2. 347519us : Unknown type 6
[ 0.456075] -0 0dN.2. 353141us : Unknown type 6
[ 0.456075] -0 0dN.2. 358684us : Unknown type 6
This is because the trace_printk() event (type 6) hasnt been registered
yet. That gets done via an early_initcall(), which may be early, but not
early enough.
Instead of registering the trace_printk() event (and other ftrace events,
which are not trace events) via an early_initcall(), have them registered at
the same time that trace_printk() can be used. This way, if there is a
crash before early_initcall(), then the trace_printk()s will actually be
useful.