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perf/amd/ibs: Avoid calling perf_allow_kernel() from the IBS NMI handler

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Calling perf_allow_kernel() from the NMI context is unsafe and could be
fatal. Capture the permission at event-initialization time by storing it
in event->hw.flags, and have the NMI handler rely on that cached flag
instead of making the call directly.

Fixes: 50a53b60e1 ("perf/amd/ibs: Prevent leaking sensitive data to userspace")
Reported-by: Sadasivan Shaiju <sadasivan.shaiju2@amd.com>
Signed-off-by: Ravi Bangoria <ravi.bangoria@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Link: https://patch.msgid.link/20260216042216.1440-5-ravi.bangoria@amd.com
This commit is contained in:
Ravi Bangoria 2026-02-16 04:22:15 +00:00 committed by Peter Zijlstra
parent 723a290326
commit b0a0914262
2 changed files with 5 additions and 1 deletions
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5
arch/x86/events/amd/ibs.c
View File

@ -313,6 +313,9 @@ static int perf_ibs_init(struct perf_event *event)
if (ret)
return ret;
if (perf_allow_kernel())
hwc->flags |= PERF_X86_EVENT_UNPRIVILEGED;
if (hwc->sample_period) {
if (config & perf_ibs->cnt_mask)
/* raw max_cnt may not be set */
@ -1349,7 +1352,7 @@ static int perf_ibs_handle_irq(struct perf_ibs *perf_ibs, struct pt_regs *iregs)
* unprivileged users.
*/
if ((event->attr.sample_type & PERF_SAMPLE_RAW) &&
perf_allow_kernel()) {
(hwc->flags & PERF_X86_EVENT_UNPRIVILEGED)) {
perf_ibs_phyaddr_clear(perf_ibs, &ibs_data);
}

1
arch/x86/events/perf_event_flags.h
View File

@ -23,3 +23,4 @@ PERF_ARCH(PEBS_LAT_HYBRID, 0x0020000) /* ld and st lat for hybrid */
PERF_ARCH(NEEDS_BRANCH_STACK, 0x0040000) /* require branch stack setup */
PERF_ARCH(BRANCH_COUNTERS, 0x0080000) /* logs the counters in the extra space of each branch */
PERF_ARCH(ACR, 0x0100000) /* Auto counter reload */
PERF_ARCH(UNPRIVILEGED, 0x0200000) /* Unprivileged event (wrt perf_allow_kernel()) */