> On Fri, Jan 17, 2025 at 12:23:53PM +0530, Basharath Hussain Khaja wrote:
>> >> >> Thomas Weißschuh <thomas.weissschuh@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
>> >> >> > ---
>> >> >> > 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.
>> >>
>> >>
>> >> This commit is breaking Ethernet functionality on the TI AM57xx platform due to
>> >> zero byte SRAM block size allocation during initialization. Prior to this
>> >> patch, zero byte block sizes were handled properly.
>> >
>> > What driver and where exactly?
>>
>> We found an issue while developing the driver [1] and more
>> specifically in [2] (lines 313-327), but it looks like this is a
>> generic issue which can block 1 byte of memory, when a zero size
>> request has been initiated for the reserved region.
>>
>> 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 && check_add_overflow(end, size - 1, &end))
>> return -EOVERFLOW;
>> if (overflows_type(end, r->end))
>> return -EOVERFLOW;
>>
>> r->start = start;
>> r->end = end;
>>
>> return 0;
>> }
>>
>> Though we have the start address handling already in place above, we
>> do see an issue with the end address, because there is an
>> unconditional +1 afterwards in resource_size() API below which is
>> responsible for reserving the extra byte
>>
>> static inline resource_size_t resource_size(const struct resource *res)
>> {
>> return res->end - res->start + 1;
>> }
>
> Now the report makes more sense.
>
>> We have 4 ways of fixing it.
>>
>> Option 1: Modify the function to handle the size zero case
>>
>> diff --git a/drivers/of/address.c b/drivers/of/address.c
>> index c1f1c810e810..8db6ae9a12b8 100644
>> --- a/drivers/of/address.c
>> +++ b/drivers/of/address.c
>> @@ -204,6 +204,12 @@ static int __of_address_resource_bounds(struct resource *r,
>> u64 start, u64 size)
>>
>> if (overflows_type(start, r->start))
>> return -EOVERFLOW;
>> + if (!size) {
>> + r->start = start;
>> + r->end = end - 1;
>> +
>> + return 0;
>> + }
>> if (size && check_add_overflow(end, size - 1, &end))
>> return -EOVERFLOW;
>> if (overflows_type(end, r->end))
>>
>> This seems to be the simplest solution.
>
> Fixing it in __of_address_resource_bounds() looks correct to me.
> The proposed solution doesn't look as clean as I'd like though,
> this is highly subjective, though.
>
> What about the following (untested)?
>
> static int __of_address_resource_bounds(struct resource *r, u64 start, u64 size)
> {
> if (overflows_type(start, r->start))
> return -EOVERFLOW;
>
> r->start = start;
> r->end = start;
>
> if (!size)
> r->end -= 1; /* May underflow for empty resources. */
> else if (check_add_overflow(r->end, size - 1, &r->end))
> return -EOVERFLOW;
>
> return 0;
> }
>
> A kunit test looks to be in order in any case, to make sure all the
> edgecases are handled.
>
We have tested with your suggested changes as below for our functionality it is working as expected. To be on safe side we ran through patch verification tools, we found no issues.
diff --git a/drivers/of/address.c b/drivers/of/address.c
index c1f1c810e810..6e581187c122 100644
--- a/drivers/of/address.c
+++ b/drivers/of/address.c
@@ -200,17 +200,16 @@ static u64 of_bus_pci_map(__be32 *addr, const __be32 *range, int na, int ns,
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 && check_add_overflow(end, size - 1, &end))
- return -EOVERFLOW;
- if (overflows_type(end, r->end))
- return -EOVERFLOW;
r->start = start;
- r->end = end;
+ r->end = start;
+
+ if (!size)
+ r->end -= 1; /* May underflow for empty resources. */
+ else if (check_add_overflow(r->end, size - 1, &r->end))
+ return -EOVERFLOW;
return 0;
}
Thanks & Best Regards,
Basharath
