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SubjectRe: [PATCH v2 03/28] vsprintf: %pf(%p)
On Fri, May 20, 2022 at 08:03:29AM +0000, David Laight wrote:
> From: Matthew Wilcox
> > Sent: 19 May 2022 22:15
> >
> > On Thu, May 19, 2022 at 09:06:24PM +0000, David Laight wrote:
> > > I suspect this a very good way to blow the kernel stack.
> > > The highest stack use is already very likely to be inside
> > > the printf code in an error path somewhere.
> >
> > ...
> >
> > > Double copying using a temporary buffer isn't the end of the world.
> >
> > How can you hold both of these positions simultaneously?
>
> Mostly you only need a short(ish) buffer to format a single item.
> But even a full line buffer is probably less stack than a
> nested printf call.
> It certainly makes it possible for static analysis to determine
> maximum stack depth.

There are a lot of words in this response. Numbers, please.

> That made me realise that one of the problems doing static
> analysis of stack depth is indirect calls.
> The hashes that (IIRC) fine-ibt add to indirect calls
> and functions make it possible to tie these together.
> So you can determine the worst one of the called functions
> and use it for the stack depth at the call sites.
>
> David
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
>

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