From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 01C2E3451C8; Mon, 22 Jun 2026 03:59:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782100752; cv=none; b=NsNTUeM7e3H9HuYDZyO7iL2ixLnRUnP6IGYEKA9vm/Ndrm17RLI3og4HjYawPUS+KQQGWXz9UyLcaqsjDETY7VxOxJGYMhAPvjxxMOJHeMUnH71ZuRnpcOZZEw8WBb4cFxB8WpZCYlvfNbq9FWGNRkfGzWRApQsFWaCMyeuOdC8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782100752; c=relaxed/simple; bh=kB6QFowOyGZvRR6S465cpWDZhqa5nrSt8U4Ordw1wzY=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=IjzxoiWi4ycVLrsLIuZf1mwTvoohxLwG21CSpKGxbLyyMiQ2OriqlF9LL+XHiJpAN6ybboEJA48HfuvrxLdWykP2C13vZvumzSCWcAOs0lZWPLeBjfknUZuh4aBz4fU9vFalzo1i5hREDQSWMCfcln9pveR2OkT7iYrbOCLKgCY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Z3zd2fbD; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Z3zd2fbD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 90FCD1F000E9; Mon, 22 Jun 2026 03:59:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782100750; bh=w5m8O+NPja5s16yXb+EGXUVGCTi5ADiUilH0E9bcCEA=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=Z3zd2fbD7WPyACQiA3E2DG2r3L7nKgKfjDhVFJBreccTNe6Pkn6GN08RLLMJU836D Y4xBG1Ss0EWQMHEYunrc0lLtoefgB15eJmtxGPTZQ6yuUHxBUOexyOJlUoCgvrs3y+ uFRphMnzycPb7t+HhWJ86aP4qgvO711PscaFBOiS29x18gAZp+kAXIdy1NY5GwNSRh D0nl9G7nD7CjruvCzONWLusB2OoXcQ3+nTMfWwC4M1WU8lmS46JNnRQeljgR9Fc6WN 9DI/BWXEppXqFR4tmArHi75hNboaL4VSZxInIavxPytFtmfjy2HsNae9K4MHhWAzKG lC87/O9mXUwTw== Date: Mon, 22 Jun 2026 12:59:08 +0900 From: Masami Hiramatsu (Google) To: Martin Kaiser Cc: Steven Rostedt , linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] tracing: eprobe: read the complete FILTER_PTR_STRING pointer Message-Id: <20260622125908.edfca672f28208ecac97091f@kernel.org> In-Reply-To: <20260620145339.3234726-1-martin@kaiser.cx> References: <20260620145339.3234726-1-martin@kaiser.cx> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Sat, 20 Jun 2026 16:48:59 +0200 Martin Kaiser wrote: > For a char * element in an event, the FILTER_PTR_STRING filter type is > used. When the event occurs, a pointer is stored in the ringbuffer. > > If an eprobe references such a char * element of a "base event", the > stored pointer is truncated when it's read from the ringbuffer. > > $ cd /sys/kernel/tracing > $ echo 'e rcu.rcu_utilization $s:x64 $s:string' > dynamic_events > $ echo 1 > tracing_on > $ echo 1 > events/eprobes/enable > $ sleep 1 > $ echo 0 > events/eprobes/enable > $ cat trace > -0 ...: (rcu.rcu_utilization) arg1=0x4f arg2=(fault) > -0 ...: (rcu.rcu_utilization) arg1=0x2 arg2=(fault) > > The problem is in get_event_field > > val = (unsigned long)(*(char *)addr); > > addr points to the position in the ringbuffer where the pointer was > stored. The assignment reads only the lowest byte of the pointer. > > Fix the cast to read the whole pointer. The output of the test above > is now > > -0 ... arg1=0xffffffff81c7d3f3 arg2="Start scheduler-tick" > -0 ... arg1=0xffffffff81c57340 arg2="End scheduler-tick" This looks good to me. Let me pick it. Thanks! > > Fixes: f04dec93466a ("tracing/eprobes: Fix reading of string fields") > Signed-off-by: Martin Kaiser > --- > v2 > - use rcu event as an example, don't dereference a user pointer > - add Fixes tag > > kernel/trace/trace_eprobe.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/trace/trace_eprobe.c b/kernel/trace/trace_eprobe.c > index b66d6196338d..50518b071414 100644 > --- a/kernel/trace/trace_eprobe.c > +++ b/kernel/trace/trace_eprobe.c > @@ -315,7 +315,7 @@ get_event_field(struct fetch_insn *code, void *rec) > val = (unsigned long)addr; > break; > case FILTER_PTR_STRING: > - val = (unsigned long)(*(char *)addr); > + val = *(unsigned long *)addr; > break; > default: > WARN_ON_ONCE(1); > -- > 2.43.7 > -- Masami Hiramatsu (Google)