From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 660CD1CEEB6; Sun, 24 Nov 2024 12:41:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732452066; cv=none; b=D5805D2QitN4rZmBBofBjX6gRLykXfU+RJOXFLpnvALxAUhwZGWNIzPyZUQFyc3z+GzGSDCtCtxg3BcybIJwusE74tJ/5F9izvW3p61c56ohbSrNDxQV3XiLGj+tAz/O4uqgFWZG6b1WDWNcWp31UFwAOGK8gHGLHqc7OqawUXo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732452066; c=relaxed/simple; bh=dErbjV7sTVPI4x0pZOh2XL755cG5ybJwjqwnnLGyu00=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=GMAw2RQbaRtHgy9CBIIN/Fq/3wQvHgw0HaRO3of1D0nB6DnOIAeh0Sb5jdtO231rO4K7QoQnNexo7D6PU8y0Ozof0EzbkFr6+uGcg1UlkpLMiFSF2+z8KsINo9qCn6zhRROtqdIGKL3vlgouIsWBeLgfAqsraWkRr5Ebqlj5WjU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ONtap4VV; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ONtap4VV" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CD1DAC4CECC; Sun, 24 Nov 2024 12:41:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1732452066; bh=dErbjV7sTVPI4x0pZOh2XL755cG5ybJwjqwnnLGyu00=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ONtap4VVB/Qi4R0GRtG3D9LNlocLJEkPkRxZSRQNAOvj2b0LprMzwsZqT2r2wjMMz kTdBXWEuPRFoZoDlnO0RVPhHsD7rlaNL/c6jctVtUbqIl+GU8K01rZnu36TDnrVqT2 U5Z5dpBZA7LqXXHmv5Tz+trmgxK73N1KGTlbVdHsZxyC27mhL4iwnzp5j1I697rJJD dnZCQNKCiiuvOI6OBK9yzbUvIK6ocqeRDvnryZtO2ho1DxR97VvwOREl6paUZlIKMz PtbwZfGxUc8DgI9uoK+e9WS9Xbi+N5S3i7lAqKSGFhyFraj1cqKHTtVbq4ckEeEE7d IfPSMPBgobOhA== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Thomas Richter , Hendrik Brueckner , Heiko Carstens , Sasha Levin , gor@linux.ibm.com, agordeev@linux.ibm.com, sumanthk@linux.ibm.com, linux-s390@vger.kernel.org Subject: [PATCH AUTOSEL 6.6 3/9] s390/cpum_sf: Handle CPU hotplug remove during sampling Date: Sun, 24 Nov 2024 07:40:41 -0500 Message-ID: <20241124124057.3336453-3-sashal@kernel.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20241124124057.3336453-1-sashal@kernel.org> References: <20241124124057.3336453-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 6.6.63 Content-Transfer-Encoding: 8bit From: Thomas Richter [ Upstream commit a0bd7dacbd51c632b8e2c0500b479af564afadf3 ] CPU hotplug remove handling triggers the following function call sequence: CPUHP_AP_PERF_S390_SF_ONLINE --> s390_pmu_sf_offline_cpu() ... CPUHP_AP_PERF_ONLINE --> perf_event_exit_cpu() The s390 CPUMF sampling CPU hotplug handler invokes: s390_pmu_sf_offline_cpu() +--> cpusf_pmu_setup() +--> setup_pmc_cpu() +--> deallocate_buffers() This function de-allocates all sampling data buffers (SDBs) allocated for that CPU at event initialization. It also clears the PMU_F_RESERVED bit. The CPU is gone and can not be sampled. With the event still being active on the removed CPU, the CPU event hotplug support in kernel performance subsystem triggers the following function calls on the removed CPU: perf_event_exit_cpu() +--> perf_event_exit_cpu_context() +--> __perf_event_exit_context() +--> __perf_remove_from_context() +--> event_sched_out() +--> cpumsf_pmu_del() +--> cpumsf_pmu_stop() +--> hw_perf_event_update() to stop and remove the event. During removal of the event, the sampling device driver tries to read out the remaining samples from the sample data buffers (SDBs). But they have already been freed (and may have been re-assigned). This may lead to a use after free situation in which case the samples are most likely invalid. In the best case the memory has not been reassigned and still contains valid data. Remedy this situation and check if the CPU is still in reserved state (bit PMU_F_RESERVED set). In this case the SDBs have not been released an contain valid data. This is always the case when the event is removed (and no CPU hotplug off occured). If the PMU_F_RESERVED bit is not set, the SDB buffers are gone. Signed-off-by: Thomas Richter Reviewed-by: Hendrik Brueckner Signed-off-by: Heiko Carstens Signed-off-by: Sasha Levin --- arch/s390/kernel/perf_cpum_sf.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/arch/s390/kernel/perf_cpum_sf.c b/arch/s390/kernel/perf_cpum_sf.c index a3169193775f7..e52c89739bc9a 100644 --- a/arch/s390/kernel/perf_cpum_sf.c +++ b/arch/s390/kernel/perf_cpum_sf.c @@ -1922,7 +1922,9 @@ static void cpumsf_pmu_stop(struct perf_event *event, int flags) event->hw.state |= PERF_HES_STOPPED; if ((flags & PERF_EF_UPDATE) && !(event->hw.state & PERF_HES_UPTODATE)) { - hw_perf_event_update(event, 1); + /* CPU hotplug off removes SDBs. No samples to extract. */ + if (cpuhw->flags & PMU_F_RESERVED) + hw_perf_event_update(event, 1); event->hw.state |= PERF_HES_UPTODATE; } perf_pmu_enable(event->pmu); -- 2.43.0