linux-kernel - Re: [PATCH v4 0/3] Compile-time stack frame pointer validation

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Date:	Wed, 20 May 2015 12:33:39 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Josh Poimboeuf <jpoimboe@...hat.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Michal Marek <mmarek@...e.cz>,
	Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 0/3] Compile-time stack frame pointer validation


* Josh Poimboeuf <jpoimboe@...hat.com> wrote:

> In discussions around the live kernel patching consistency model RFC
> [1], Peter and Ingo correctly pointed out that stack traces aren't
> reliable.  And as Ingo said, there's no "strong force" which ensures we
> can rely on them.
> 
> So I've been thinking about how to fix that.  My goal is to eventually
> make stack traces reliable.  Or at the very least, to be able to detect
> at runtime when a given stack trace *might* be unreliable.  But improved
> stack traces would broadly benefit the entire kernel, regardless of the
> outcome of the live kernel patching consistency model discussions.
> 
> This patch set is just the first in a series of proposed stack trace
> reliability improvements.  Future proposals will include runtime stack
> reliability checking, as well as compile-time and runtime DWARF
> validations.
> 
> As far as I can tell, there are two main obstacles which prevent frame
> pointer based stack traces from being reliable:
> 
> 1) Missing frame pointer logic: currently, most assembly functions don't
>    set up the frame pointer.

Could you please paste here the output of what the new checks print 
for x86/64 defconfig?

> As a first step, all reported non-compliances result in warnings.  
> Right now I'm seeing 200+ warnings.  Once we get them all cleaned 
> up, we can change the warnings to build errors so the asm code can 
> stay clean.

That's quite a bit ...

Thanks,

	Ingo
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