linux-kernel - Re: [RFC 0/5] kernel: backtrace unwind support

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Date:	Tue, 14 Feb 2012 13:22:24 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Jiri Olsa <jolsa@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, paulus@...ba.org,
	cjashfor@...ux.vnet.ibm.com, fweisbec@...il.com,
	linux-kernel@...r.kernel.org,
	"James E.J. Bottomley" <jejb@...isc-linux.org>,
	Jan Blunck <jblunck@...e.de>
Subject: Re: [RFC 0/5] kernel: backtrace unwind support

On Fri, 2012-02-10 at 12:37 -0800, Linus Torvalds wrote:
> On Fri, Feb 10, 2012 at 12:18 PM, Jiri Olsa <jolsa@...hat.com> wrote:
> >
> > yep, looks interesting.. not sure about the mathematical proof though ;)
> 
> Well, I can already say what the old code did horribly horribly wrong:
> 
>  - *all* stack accesses need to go through a validation function, they
> can never *ever* just try to access the stack.
> 
>     The validation function really needs to really check the full
> range of the stack area, not something random.
> 
>  - all dwarf information accesses need to similarly validate the
> access, and accept that sometimes the dwarf info is simply missing or
> actively wrong.

In addition it should all go through something like
copy_from_user_inatomic(), ie, all access to that stuff should have
built-in fault recovery without triggering high level page faults, stack
expansion etc...

Cheers,
Ben.


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