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

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Message-ID: <87mskbqher.fsf@mail.lhotse>
Date: Sat, 14 Sep 2024 09:10:20 +1000
From: Michael Ellerman <mpe@...erman.id.au>
To: Rob Herring <robh@...nel.org>
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

Rob Herring <robh@...nel.org> writes:
> 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.

Thanks.

cheers