From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 239A5481FB3 for ; Fri, 6 Mar 2026 21:13:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772831633; cv=none; b=PDGT4LSdUshHP0oCwPcZU13cKfl+OpuKnhhHWv9W/9zhoSeToA9ToGTZwzj4dRPjOv+lp/z/QvG/YaJ4MRdeAdJY/aLBwgNhJZM6ut6FDPD8Fw2SxW2ndlZCwz4iStUT1lGTolQfZV3hLtk333vS8s8CWZ6DKsghg+QZGfebS2s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772831633; c=relaxed/simple; bh=xLeiiAuxWI4SWc08bgqVdeXt16JUlRLlLuCLPKDnrWA=; h=Date:From:To:cc:Subject:In-Reply-To:Message-ID:References: MIME-Version:Content-Type; b=HWqv6OWvk5YvdTJugV08YmXzQSXDLTR+jgJHxjQr8/BzIEWI893DKAoWa24RUdvb7kgyOTXn/1txxfQ3dUzEkD0rjyujAB2pRfe3PWZBmk8XWsTHhwARSaZ7QtRKQ4kSrmUN9uzaa4d+mfOX5c1r4z9CfgQwfcNIx3UBxXEWdns= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=YWpikRpF; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="YWpikRpF" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1772831631; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=wjUwOnsjFj7x2OOTndf56oD3Bdw2XZlDeep7pBKBPdQ=; b=YWpikRpFVUuZd2mATBNl5UbiqXT1fTvz43M6B/rncDRNAKfM4/SuQdj6EoNIQPUSLM2GtA cS8utO7YXMhy+rZb3UzhemTQzRuAuP5+j1AWlAS+BvkBf9RchTm1ce9n5IiqXGYyBaZZqG 3nwLKq2CdW88UlKqyfW/TLaXiThCbjU= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-133-wlCPo-W2OZ-cmwgxRCxpPQ-1; Fri, 06 Mar 2026 16:13:46 -0500 X-MC-Unique: wlCPo-W2OZ-cmwgxRCxpPQ-1 X-Mimecast-MFC-AGG-ID: wlCPo-W2OZ-cmwgxRCxpPQ_1772831623 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 9481E19560A3; Fri, 6 Mar 2026 21:13:43 +0000 (UTC) Received: from Carbon (unknown [10.45.242.4]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 792931958DC5; Fri, 6 Mar 2026 21:13:33 +0000 (UTC) Date: Fri, 6 Mar 2026 22:13:27 +0100 (CET) From: Michael Petlan To: Ravi Bangoria cc: Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Ian Rogers , Dapeng Mi , James Clark , Sadasivan Shaiju , x86@kernel.org, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, Manali Shukla , Santosh Shukla , Ananth Narayan , Sandipan Das Subject: Re: [PATCH v2 4/5] perf/amd/ibs: Avoid calling perf_allow_kernel() from the IBS NMI handler In-Reply-To: <20260216042216.1440-5-ravi.bangoria@amd.com> Message-ID: References: <20260216042216.1440-1-ravi.bangoria@amd.com> <20260216042216.1440-5-ravi.bangoria@amd.com> Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 On Mon, 16 Feb 2026, Ravi Bangoria wrote: > 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. > Hi Ravi. I have tested this fix on a machine (below), which without this fix can be easily crashed by recording ibs_op/l3missonly=1/ event. With this fix, it survived 4900+ iterations without any crash. CPU details =========== BIOS CPU family: 107 CPU family: 26 Model: 2 Stepping: 1 Thanks for fixing. Cheers, Michael > Reported-by: Sadasivan Shaiju > Fixes: 50a53b60e141d ("perf/amd/ibs: Prevent leaking sensitive data to userspace") > Signed-off-by: Ravi Bangoria Tested-by: Michael Petlan > --- > arch/x86/events/amd/ibs.c | 5 ++++- > arch/x86/events/perf_event_flags.h | 1 + > 2 files changed, 5 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/events/amd/ibs.c b/arch/x86/events/amd/ibs.c > index 05b7c9f2ec33..004226b52ac7 100644 > --- a/arch/x86/events/amd/ibs.c > +++ b/arch/x86/events/amd/ibs.c > @@ -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); > } > > diff --git a/arch/x86/events/perf_event_flags.h b/arch/x86/events/perf_event_flags.h > index 70078334e4a3..47f84ee8f540 100644 > --- a/arch/x86/events/perf_event_flags.h > +++ b/arch/x86/events/perf_event_flags.h > @@ -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()) */ > -- > 2.43.0 > > >