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

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Message-ID: <YLjZYvXnuPnbXzOm@hirez.programming.kicks-ass.net>
Date:   Thu, 3 Jun 2021 15:30:10 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     Josh Poimboeuf <jpoimboe@...hat.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>
Subject: Re: [syzbot] KASAN: stack-out-of-bounds Read in profile_pc

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.