01c8f9806b
In kcov_remote_start()/kcov_remote_stop(), we swap the previous KCOV metadata of the current task into a per-CPU variable. However, the kcov_mode_enabled(mode) check is not sufficient in the case of remote KCOV coverage: current->kcov_mode always remains KCOV_MODE_DISABLED for remote KCOV objects. If the original task that has invoked the KCOV_REMOTE_ENABLE ioctl happens to get interrupted and kcov_remote_start() is called, it ultimately leads to kcov_remote_stop() NOT restoring the original KCOV reference. So when the task exits, all registered remote KCOV handles remain active forever. The most uncomfortable effect (at least for syzkaller) is that the bug prevents the reuse of the same /sys/kernel/debug/kcov descriptor. If we obtain it in the parent process and then e.g. drop some capabilities and continuously fork to execute individual programs, at some point current->kcov of the forked process is lost, kcov_task_exit() takes no action, and all KCOV_REMOTE_ENABLE ioctls calls from subsequent forks fail. And, yes, the efficiency is also affected if we keep on losing remote kcov objects. a) kcov_remote_map keeps on growing forever. b) (If I'm not mistaken), we're also not freeing the memory referenced by kcov->area. Fix it by introducing a special kcov_mode that is assigned to the task that owns a KCOV remote object. It makes kcov_mode_enabled() return true and yet does not trigger coverage collection in __sanitizer_cov_trace_pc() and write_comp_data(). [nogikh@google.com: replace WRITE_ONCE() with an ordinary assignment] Link: https://lkml.kernel.org/r/20240614171221.2837584-1-nogikh@google.com Link: https://lkml.kernel.org/r/20240611133229.527822-1-nogikh@google.com Fixes: 5ff3b30ab57d ("kcov: collect coverage from interrupts") Signed-off-by: Aleksandr Nogikh <nogikh@google.com> Reviewed-by: Dmitry Vyukov <dvyukov@google.com> Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com> Tested-by: Andrey Konovalov <andreyknvl@gmail.com> Cc: Alexander Potapenko <glider@google.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Marco Elver <elver@google.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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.