- Replace trace_check_vprintf() with test_event_printk() and ignore_event()
The function test_event_printk() checks on boot up if the trace event
printf() formats dereference any pointers, and if they do, it then looks
at the arguments to make sure that the pointers they dereference will
exist in the event on the ring buffer. If they do not, it issues a
WARN_ON() as it is a likely bug.
But this isn't the case for the strings that can be dereferenced with
"%s", as some trace events (notably RCU and some IPI events) save
a pointer to a static string in the ring buffer. As the string it
points to lives as long as the kernel is running, it is not a bug
to reference it, as it is guaranteed to be there when the event is read.
But it is also possible (and a common bug) to point to some allocated
string that could be freed before the trace event is read and the
dereference is to bad memory. This case requires a run time check.
The previous way to handle this was with trace_check_vprintf() that would
process the printf format piece by piece and send what it didn't care
about to vsnprintf() to handle arguments that were not strings. This
kept it from having to reimplement vsnprintf(). But it relied on va_list
implementation and for architectures that copied the va_list and did
not pass it by reference, it wasn't even possible to do this check and
it would be skipped. As 64bit x86 passed va_list by reference, most
events were tested and this kept out bugs where strings would have been
dereferenced after being freed.
Instead of relying on the implementation of va_list, extend the boot up
test_event_printk() function to validate all the "%s" strings that
can be validated at boot, and for the few events that point to strings
outside the ring buffer, flag both the event and the field that is
dereferenced as "needs_test". Then before the event is printed, a call
to ignore_event() is made, and if the event has the flag set, it iterates
all its fields and for every field that is to be tested, it will read
the pointer directly from the event in the ring buffer and make sure
that it is valid. If the pointer is not valid, it will print a WARN_ON(),
print out to the trace that the event has unsafe memory and ignore
the print format.
With this new update, the trace_check_vprintf() can be safely removed
and now all events can be verified regardless of architecture.
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Merge tag 'trace-v6.13-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace
Pull tracing fixes from Steven Rostedt:
"Replace trace_check_vprintf() with test_event_printk() and
ignore_event()
The function test_event_printk() checks on boot up if the trace event
printf() formats dereference any pointers, and if they do, it then
looks at the arguments to make sure that the pointers they dereference
will exist in the event on the ring buffer. If they do not, it issues
a WARN_ON() as it is a likely bug.
But this isn't the case for the strings that can be dereferenced with
"%s", as some trace events (notably RCU and some IPI events) save a
pointer to a static string in the ring buffer. As the string it points
to lives as long as the kernel is running, it is not a bug to
reference it, as it is guaranteed to be there when the event is read.
But it is also possible (and a common bug) to point to some allocated
string that could be freed before the trace event is read and the
dereference is to bad memory. This case requires a run time check.
The previous way to handle this was with trace_check_vprintf() that
would process the printf format piece by piece and send what it didn't
care about to vsnprintf() to handle arguments that were not strings.
This kept it from having to reimplement vsnprintf(). But it relied on
va_list implementation and for architectures that copied the va_list
and did not pass it by reference, it wasn't even possible to do this
check and it would be skipped. As 64bit x86 passed va_list by
reference, most events were tested and this kept out bugs where
strings would have been dereferenced after being freed.
Instead of relying on the implementation of va_list, extend the boot
up test_event_printk() function to validate all the "%s" strings that
can be validated at boot, and for the few events that point to strings
outside the ring buffer, flag both the event and the field that is
dereferenced as "needs_test". Then before the event is printed, a call
to ignore_event() is made, and if the event has the flag set, it
iterates all its fields and for every field that is to be tested, it
will read the pointer directly from the event in the ring buffer and
make sure that it is valid. If the pointer is not valid, it will print
a WARN_ON(), print out to the trace that the event has unsafe memory
and ignore the print format.
With this new update, the trace_check_vprintf() can be safely removed
and now all events can be verified regardless of architecture"
* tag 'trace-v6.13-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
tracing: Check "%s" dereference via the field and not the TP_printk format
tracing: Add "%s" check in test_event_printk()
tracing: Add missing helper functions in event pointer dereference check
tracing: Fix test_event_printk() to process entire print argument
c061cf420d