linux-kernel - Re: [syzbot] KASAN: stack-out-of-bounds Read in profile

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Message-ID: <20210603133914.j2aeadmvhncnlk5q@treble>
Date:   Thu, 3 Jun 2021 08:39:14 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Andi Kleen <ak@...ux.intel.com>,
        syzbot <syzbot+84fe685c02cd112a2ac3@...kaller.appspotmail.com>,
        bp@...en8.de, hpa@...or.com, inglorion@...gle.com,
        linux-kernel@...r.kernel.org, mingo@...hat.com,
        syzkaller-bugs@...glegroups.com, tglx@...utronix.de,
        x86@...nel.org, Andy Lutomirski <luto@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [syzbot] KASAN: stack-out-of-bounds Read in profile_pc

On Thu, Jun 03, 2021 at 03:30:10PM +0200, Peter Zijlstra wrote:
> On Wed, Jun 02, 2021 at 04:35:11PM -0700, Andi Kleen wrote:
> 
> > > We could just use ORC to unwind to the next frame.  Though, isn't
> > > /proc/profile redundant, compared to all the more sophisticated options
> > > nowadays?  Is there still a distinct use case for it or can we just
> > > remove it?
> > 
> > It's still needed for some special cases. For example there is no other
> > viable way to profile early boot without a VM
> > 
> > I would just drop the hack to unwind, at least for the early boot profile
> > use case locking profiling is usually not needed.
> 
> Surely we can cook up something else there and delete this thing? ftrace
> buffers are available really early, it shouldn't be hard to dump some
> data in there during boot.

True, ftrace does have function profiling (function_profile_enabled).

Steve, is there a way to enable that on the kernel cmdline?

-- 
Josh