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 253061AC891; Sun, 24 Nov 2024 12:42:26 +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=1732452147; cv=none; b=CmZvbNEhkwHvDmlNfTacfTCtcjI8blwjrVuBSOLV7ZwmdXYlAMxIKmoiiBhELwLvLewgA0vEuNgYsnlVfv/4Fjj72vH8AL2+AoH3xNvdQdIU5Y2TOOVR3cGStQvPhauZR8bNZFBzCLhv7PpGALxltZwWUuahtBAvsuZFJ9FiQEQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732452147; c=relaxed/simple; bh=olyvTspdfHDyt5B6QxXNZzVEsAjT24Xn76a+us0aN3w=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=K8U2+jQHifIyogWDeYwDYEZKL9XnIE/9sqxo3mUQoRILZkspeKD90gcLIZT03395464HqDPDR7cMn56gjZOnsHgAoxmEvnuHYnXITyw1g2ue4xs5s5ZGSi88f92lUhoITss/ta2fp0it7rV8Tl6SgkRH5vFE/Hxbl2fjRTbm/mY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=hLX34YBA; 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="hLX34YBA" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 91844C4CECC; Sun, 24 Nov 2024 12:42:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1732452146; bh=olyvTspdfHDyt5B6QxXNZzVEsAjT24Xn76a+us0aN3w=; h=From:To:Cc:Subject:Date:From; b=hLX34YBApSzCVjSA+OmJrpiTSTZ/WmQVp8wF8WIIdiHCHgiUdRH3UOLF84MtT8GEB JwoAtj28h8qakICw0gNEc/giwzeaU4jDh8eumUqgYTlh0PAerCYNoAsd4vwAhRrvt1 n5FhJhem1gD2k43AxJpPhJWAQqHKMXuo9Qp8jv84f7Z2azZ9g5N6gntQqqEjuR5SQD 9feR7d2hgutIiLfFNg6r1NRFwDtMdEJ4tSTB8tUETB73p7URNWsDwL7ucOLRiqiM6J J01WvPvKd2fal37nJIhy0q2WoqlhIXjf4RWlN7I0YUSRwIKOSWvv1RsgfhMUaxaq1E F5LUA+my5P89w== 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 5.4 1/2] s390/cpum_sf: Handle CPU hotplug remove during sampling Date: Sun, 24 Nov 2024 07:42:20 -0500 Message-ID: <20241124124224.3337144-1-sashal@kernel.org> X-Mailer: git-send-email 2.43.0 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 5.4.286 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 4f251cd624d7e..6047ccb6f8e26 100644 --- a/arch/s390/kernel/perf_cpum_sf.c +++ b/arch/s390/kernel/perf_cpum_sf.c @@ -1862,7 +1862,9 @@ 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