In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
perf\/x86\/intel\/pt: Fix stop\/start with no update<\/p>\n
If pt_event_stop() is called without PERF_EF_UPDATE flag, then
\nperf_aux_output_end() is not called. A subsequent call to pt_event_start()
\nwill call perf_aux_output_begin() again which violates the rule against
\nnesting and triggers a WARNING in perf_aux_output_begin().<\/p>\n
Originally, pt_event_stop() was never called without PERF_EF_UPDATE,
\nbecause the only code paths to do so are from event overflow, and Intel PT
\ndoes not do that.<\/p>\n
However the introduction of group throttling by commit 9734e25fbf5ae
\n(“perf: Fix the throttle logic for a group”) meant that an Intel PT event
\ncould be throttled if it was part of a group. Throttling calls PMU
\n ->stop() \/ ->start() callbacks without flags.<\/p>\n
An example is when AUX area sampling is used. The following commands
\nhit the issue:<\/p>\n
echo 10000 > \/proc\/sys\/kernel\/perf_event_max_sample_rate<\/p>\n
perf record -F32000 –aux-sample -e ‘{intel_pt\/\/u,cycles:u}’
\n — bash -c ‘for i in `seq 1 100000` ; do true ; done’<\/p>\n
Use PERF_HES_UPTODATE to track whether perf_aux_output_begin() and
\nperf_aux_output_end() are balanced. A cleared PERF_HES_UPTODATE bit
\nindicates that an AUX output context is still open.<\/p>\n
Amend pt_event_start() \/ pt_event_stop() accordingly so that begin\/end
\nstay balanced:<\/p>\n
– In non-snapshot mode, stop() always closes the buffer (the buffer may
\n have run out of space, and that accounting is done by the update), so
\n a following start() opens a fresh one as before.<\/p>\n
– In snapshot\/overwrite mode, stop() without PERF_EF_UPDATE leaves the
\n buffer open so that pt_event_snapshot_aux() can still copy from it,
\n and start() then only re-enables tracing instead of calling
\n perf_aux_output_begin() again.<\/p>\n
Note that pt_event_del() calls pt_event_stop() with PERF_EF_UPDATE flag set
\n(as is required by the documentation), so a final call to
\nperf_aux_output_end() is assured.<\/p>\n","protected":false},"excerpt":{"rendered":"
In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
perf\/x86\/intel\/pt: Fix stop\/start with no update<\/p>\n
If pt_event_stop() is called without PERF_EF_UPDATE flag, then
\nperf_aux_output_en<\/p>\n","protected":false},"template":"","meta":[],"categories":[],"tags":[],"class_list":["post-28539","vuln","type-vuln","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln\/28539","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln"}],"about":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/types\/vuln"}],"wp:attachment":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=28539"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=28539"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=28539"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}