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c061cf420d
- 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. -----BEGIN PGP SIGNATURE----- iIoEABYIADIWIQRRSw7ePDh/lE+zeZMp5XQQmuv6qgUCZ2IqiRQccm9zdGVkdEBn b29kbWlzLm9yZwAKCRAp5XQQmuv6qlfgAP9hJFl6zhA5GGRo905G9JWFHkbNNjgp WfQ0oMU2Eo1q+AEAmb5d3wWfWJAa+AxiiDNeZ28En/+ZbmjhSe6fPpR4egU= =LRKi -----END PGP SIGNATURE----- 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 |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.