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

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Message-ID: <20150522222251.GE20555@treble.redhat.com>
Date:	Fri, 22 May 2015 17:22:51 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...nel.org>,
	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,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Brian Gerst <brgerst@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v4 0/3] Compile-time stack frame pointer validation

On Fri, May 22, 2015 at 11:18:57PM +0200, Jiri Kosina wrote:
> On Fri, 22 May 2015, Josh Poimboeuf wrote:
> 
> > Hm, alternatives do complicate things a bit.  It *is* a false positive,
> > but not necessarily because its part of an alternative instruction
> > block.
> > 
> > The above code would be patched into memmove(), which is a leaf function
> > because it doesn't call any other functions.  Leaf functions don't need
> > frame pointer logic, so we can ignore them.
> > 
> > If instead the above code were patched into a non-leaf function, we'd
> > have to change it to restore the frame pointer before returning.
> 
> Is this really only a problem of alternatives? How about 
> dynamically-enabled tracepoints?

I think tracepoints are only in C code, right?  stackvalidate only
analyzes asm code, so it's not a concern for this patch set.

And I think tracepoints rely on normal call instructions, so they
shouldn't cause any problems with frame pointers as far as I can tell.

-- 
Josh
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