linux-kernel - Re: [PATCH 1/2] x86, stackvalidate: Compile-time stack frame pointer validation

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Message-ID: <20150428142655.GG5029@twins.programming.kicks-ass.net>
Date:	Tue, 28 Apr 2015 16:26:55 +0200
From:	Peter Zijlstra <peterz@...radead.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>,
	x86@...nel.org, live-patching@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] x86, stackvalidate: Compile-time stack frame pointer
 validation

On Tue, Apr 28, 2015 at 09:21:05AM -0500, Josh Poimboeuf wrote:

> > > I tried that, but I discovered that gcc's usage of frame pointers would
> > > be a lot harder to validate.  It only sets up the frame pointer in code
> > > paths which have call instructions.  There are a lot of functions which
> > > have conditional jumps at the beginning which can jump straight to a
> > > return instruction without first doing the frame pointer setup.
> > 
> > Hmm, would not such code break your patching?
> 
> No, because we'll also do some runtime stack validation (which will be a
> future patch set).  If we detect preemption or an irq frame on the
> stack, we'll assume the stack is unreliable and delay the patching of
> the task (*).

Ah, which fixes your second issue too (the interrupt before frame
setup). OK.

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