linux-kernel - Re: [PATCH] of: address: Unify resource bounds overflow checking

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Message-ID: <CAL_JsqLYQyue9WyYiQPaM1D8Hxve-a4RXCaDRvyeF2VWWx=Ozg@mail.gmail.com>
Date: Fri, 13 Sep 2024 13:56:37 -0500
From: Rob Herring <robh@...nel.org>
To: Michael Ellerman <mpe@...erman.id.au>
Cc: Thomas Weißschuh <thomas.weissschuh@...utronix.de>, 
	Saravana Kannan <saravanak@...gle.com>, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] of: address: Unify resource bounds overflow checking

On Fri, Sep 13, 2024 at 8:15 AM Michael Ellerman <mpe@...erman.id.au> wrote:
>
> Thomas Weißschuh <thomas.weissschuh@...utronix.de> writes:
> > The members "start" and "end" of struct resource are of type
> > "resource_size_t" which can be 32bit wide.
> > Values read from OF however are always 64bit wide.
> >
> > Refactor the diff overflow checks into a helper function.
> > Also extend the checks to validate each calculation step.
> >
> > Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
> > ---
> >  drivers/of/address.c | 45 ++++++++++++++++++++++++++-------------------
> >  1 file changed, 26 insertions(+), 19 deletions(-)
> >
> > diff --git a/drivers/of/address.c b/drivers/of/address.c
> > index 7e59283a4472..df854bb427ce 100644
> > --- a/drivers/of/address.c
> > +++ b/drivers/of/address.c
> > @@ -198,6 +198,25 @@ static u64 of_bus_pci_map(__be32 *addr, const __be32 *range, int na, int ns,
> >
> >  #endif /* CONFIG_PCI */
> >
> > +static int __of_address_resource_bounds(struct resource *r, u64 start, u64 size)
> > +{
> > +     u64 end = start;
> > +
> > +     if (overflows_type(start, r->start))
> > +             return -EOVERFLOW;
> > +     if (size == 0)
> > +             return -EOVERFLOW;
> > +     if (check_add_overflow(end, size - 1, &end))
> > +             return -EOVERFLOW;
> > +     if (overflows_type(end, r->end))
> > +             return -EOVERFLOW;
>
> This breaks PCI on powerpc qemu. Part of the PCI probe reads a resource
> that's zero sized, which used to succeed but now fails due to the size
> check above.
>
> The diff below fixes it for me.

I fixed it up with your change.


> It leaves r.end == r.start, which is fine in my case, because the code
> only uses r.start.
>
> And it seems more sane than the old code which would return
> end = start - 1, for zero sized resources.
>
> cheers
>
>
> diff --git a/drivers/of/address.c b/drivers/of/address.c
> index df854bb427ce..a001e789a6c4 100644
> --- a/drivers/of/address.c
> +++ b/drivers/of/address.c
> @@ -204,9 +204,7 @@ static int __of_address_resource_bounds(struct resource *r, u64 start, u64 size)
>
>         if (overflows_type(start, r->start))
>                 return -EOVERFLOW;
> -       if (size == 0)
> -               return -EOVERFLOW;
> -       if (check_add_overflow(end, size - 1, &end))
> +       if (size > 0 && check_add_overflow(end, size - 1, &end))
>                 return -EOVERFLOW;
>         if (overflows_type(end, r->end))
>                 return -EOVERFLOW;
>