[Bug 268857] pmcstat crashes on particular event/CPU combination

From: <bugzilla-noreply_at_freebsd.org>
Date: Wed, 07 Jun 2023 14:26:56 UTC

--- Comment #1 from commit-hook@FreeBSD.org ---
A commit in branch main references this bug:


commit 21f7397a61f7bff61a1221cc6340cd980a922540
Author:     Jessica Clarke <jrtc27@FreeBSD.org>
AuthorDate: 2023-06-07 14:21:18 +0000
Commit:     Jessica Clarke <jrtc27@FreeBSD.org>
CommitDate: 2023-06-07 14:24:29 +0000

    libpmc: Handle PMCALLOCATE log with PMC code on PMU event system

    On an arm64 system that reports as a Cortex A72 r0p3, running

      pmcstat -P CPU_CYCLES command

    works, but

      pmcstat -P cpu-cycles command

    does not. This is because the former uses the PMU event from the JSON
    source, resulting in pl_event in the log event being a small index
    (here, 5) into the generated events table, whilst the latter does not
    match any of the JSON events and falls back on PMC's own tables, mapping
    it to the PMC event 0x14111, i.e. PMC_EV_ARMV8_EVENT_11H. Then, when
    libpmc gets the PMCALLOCATE event, it tries to use the event as an index
    into the JSON-derived table, but doing so only makes sense for the
    former, whilst for the latter it will go way out of bounds and either
    read junk (which may trigger the != NULL assertion) or segfault. As far
    as I can tell we don't have anything lying around to tell us which of
    the two cases we're in, but we can exploit the fact that the first
    0x1000 PMC event codes are reserved, and that none of our PMU events
    tables reach that number of entries yet.

    PR:             268857
    Reviewed by:    mhorne
    MFC after:      1 month
    Differential Revision:  https://reviews.freebsd.org/D39592

 lib/libpmc/libpmc.c |  9 ++++++++-
 lib/libpmc/pmclog.c | 27 +++++++++++++++++++++------
 2 files changed, 29 insertions(+), 7 deletions(-)

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