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Evan Li 67d5a5e202 perf/x86/intel: Fix NULL event dereference crash in handle_pmi_common() 
[ Upstream commit 9415f749d3 ]

handle_pmi_common() may observe an active bit set in cpuc->active_mask
while the corresponding cpuc->events[] entry has already been cleared,
which leads to a NULL pointer dereference.

This can happen when interrupt throttling stops all events in a group
while PEBS processing is still in progress. perf_event_overflow() can
trigger perf_event_throttle_group(), which stops the group and clears
the cpuc->events[] entry, but the active bit may still be set when
handle_pmi_common() iterates over the events.

The following recent fix:

  7e772a93eb ("perf/x86: Fix NULL event access and potential PEBS record loss")

moved the cpuc->events[] clearing from x86_pmu_stop() to x86_pmu_del() and
relied on cpuc->active_mask/pebs_enabled checks. However,
handle_pmi_common() can still encounter a NULL cpuc->events[] entry
despite the active bit being set.

Add an explicit NULL check on the event pointer before using it,
to cover this legitimate scenario and avoid the NULL dereference crash.

Fixes: 7e772a93eb ("perf/x86: Fix NULL event access and potential PEBS record loss")
Reported-by: kitta <kitta@linux.alibaba.com>
Co-developed-by: kitta <kitta@linux.alibaba.com>
Signed-off-by: Evan Li <evan.li@linux.alibaba.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://patch.msgid.link/20251212084943.2124787-1-evan.li@linux.alibaba.com
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220855
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2025-12-18 14:03:41 +01:00
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README

README 

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.