Re: [PATCH] perf/x86/intel/uncore: Fix NULL pointer dereference issue in upi_fill_topology()

[Alexander Antonov <alexander.antonov@linux.intel.com>]

On 11/20/2023 10:21 PM, Liang, Kan wrote:
>
> On 2023-11-20 2:49 p.m., Alexander Antonov wrote:
>> On 11/15/2023 8:00 PM, Liang, Kan wrote:
>>> On 2023-11-15 10:13 a.m., alexander.antonov@linux.intel.com wrote:
>>>> From: Alexander Antonov <alexander.antonov@linux.intel.com>
>>>>
>>>> The NULL dereference happens inside upi_fill_topology() procedure in
>>>> case of disabling one of the sockets on the system.
>>>>
>>>> For example, if you disable the 2nd socket on a 4-socket system then
>>>> uncore_max_dies() returns 3 and inside pmu_alloc_topology() memory will
>>>> be allocated only for 3 sockets and stored in type->topology.
>>>> In discover_upi_topology() memory is accessed by socket id from
>>>> CPUNODEID
>>>> registers which contain physical ids (from 0 to 3) and on the line:
>>>>
>>>>       upi = &type->topology[nid][idx];
>>>>
>>>> out-of-bound access will happen and the 'upi' pointer will be passed to
>>>> upi_fill_topology() where it will be dereferenced.
>>>>
>>>> To avoid this issue update the code to convert physical socket id to
>>>> logical socket id in discover_upi_topology() before accessing memory.
>>>>
>>>> Fixes: f680b6e6062e ("perf/x86/intel/uncore: Enable UPI topology
>>>> discovery for Icelake Server")
>>>> Reported-by: Kyle Meyer <kyle.meyer@hpe.com>
>>>> Tested-by: Kyle Meyer <kyle.meyer@hpe.com>
>>>> Signed-off-by: Alexander Antonov <alexander.antonov@linux.intel.com>
>>>> ---
>>>>    arch/x86/events/intel/uncore_snbep.c | 10 ++++++++--
>>>>    1 file changed, 8 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/arch/x86/events/intel/uncore_snbep.c
>>>> b/arch/x86/events/intel/uncore_snbep.c
>>>> index 8250f0f59c2b..49bc27ab26ad 100644
>>>> --- a/arch/x86/events/intel/uncore_snbep.c
>>>> +++ b/arch/x86/events/intel/uncore_snbep.c
>>>> @@ -5596,7 +5596,7 @@ static int discover_upi_topology(struct
>>>> intel_uncore_type *type, int ubox_did, i
>>>>        struct pci_dev *ubox = NULL;
>>>>        struct pci_dev *dev = NULL;
>>>>        u32 nid, gid;
>>>> -    int i, idx, ret = -EPERM;
>>>> +    int i, idx, lgc_pkg, ret = -EPERM;
>>>>        struct intel_uncore_topology *upi;
>>>>        unsigned int devfn;
>>>>    @@ -5614,8 +5614,13 @@ static int discover_upi_topology(struct
>>>> intel_uncore_type *type, int ubox_did, i
>>>>            for (i = 0; i < 8; i++) {
>>>>                if (nid != GIDNIDMAP(gid, i))
>>>>                    continue;
>>>> +            lgc_pkg = topology_phys_to_logical_pkg(i);
>>>> +            if (lgc_pkg < 0) {
>>>> +                ret = -EPERM;
>>>> +                goto err;
>>>> +            }
>>> In the snbep_pci2phy_map_init(), there are similar codes to find the
>>> logical die id. Can we factor a common function for both of them?
>>>
>>> Thanks,
>>> Kan
>> Hi Kan,
>>
>> Thank you for your comment.
>> Yes, I think we can factor out the common loop where GIDNIDMAP is being
>> checked.
>> But inside snbep_pci2phy_map_init() we have a bit different procedure which
>> also does the following:
>>
>> if (topology_max_die_per_package() > 1)
>>      die_id = i;
>>
>> I think that having this code, at least, in our case could bring us to the
>> same issue which we are trying to fix. But of course we could
>> parametrize this checking.
> The topology_max_die_per_package() > 1 means there are more that 1 die
> in a socket. AFAIK, it only happens on the Cascade Lake AP.
>
> Did you observe it in the ICX?
>
> Thanks,
> Kan
No, I didn't observe it on ICX. Seems for now we have it only on CLX-AP

Thanks,
Alexander
>
>> What do you think?
>>
>> Thanks,
>> Alexander
>>>>                for (idx = 0; idx < type->num_boxes; idx++) {
>>>> -                upi = &type->topology[nid][idx];
>>>> +                upi = &type->topology[lgc_pkg][idx];
>>>>                    devfn = PCI_DEVFN(dev_link0 + idx,
>>>> ICX_UPI_REGS_ADDR_FUNCTION);
>>>>                    dev =
>>>> pci_get_domain_bus_and_slot(pci_domain_nr(ubox->bus),
>>>>                                      ubox->bus->number,
>>>> @@ -5626,6 +5631,7 @@ static int discover_upi_topology(struct
>>>> intel_uncore_type *type, int ubox_did, i
>>>>                            goto err;
>>>>                    }
>>>>                }
>>>> +            break;
>>>>            }
>>>>        }
>>>>    err:
>>>>
>>>> base-commit: 9bacdd8996c77c42ca004440be610692275ff9d0