Re: [PATCH v2 0/2] Fix get a wrong pci host bridge in cxl_setup_parent_dport()

[Dan Williams <dan.j.williams@intel.com>]

Li Ming wrote:
> The cxl_test unit test environment on qemu always hit below call trace
> with KASAN enabled:
> 
>  BUG: KASAN: slab-out-of-bounds in cxl_setup_parent_dport+0x480/0x530 [cxl_core]
>  Read of size 1 at addr ff110000676014f8 by task (udev-worker)/676[   24.424403] CPU: 2 PID: 676 Comm: (udev-worker) Tainted: G           O     N 6.10.0-qemucxl #1
>  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS edk2-20240214-2.el9 02/14/2024
>  Call Trace:
>   <TASK>
>   dump_stack_lvl+0xea/0x150
>   print_report+0xce/0x610
>   ? kasan_complete_mode_report_info+0x40/0x200
>   kasan_report+0xcc/0x110
>   __asan_report_load1_noabort+0x18/0x20
>   cxl_setup_parent_dport+0x480/0x530 [cxl_core]
>   cxl_mem_probe+0x49b/0xaa0 [cxl_mem]
> 
> The root cause is that a wrong host bridge was gotten from
> dport->dport_dev in cxl_setup_parent_dport(). In
> cxl_setup_parent_dport(), it always calls
> to_pci_host_bridge(dport->dport_dev) to get a pci_host_bridge structure.
> There are two issues in the implementation:
> 
> * to_pci_host_bridge(dport->dport_dev) should be used only for RCH
>   cases, dport->dport_dev points to a pci device rather than a pci host
>   bridge in VH cases. The solution is checking if dport is in RCH mode
>   then calling to_pci_host_bridge().
>   (Patch 1)
> 
> * In cxl_test unit test environment, cxl_test will create a emulated CXL
>   topology with emulated dports, the dport_dev of a emulated dport
>   points to a platform device. to_pci_host_bridge(dport->dport_dev) also
>   gets a wrong pci host bridge in the case. The solution is implementing
>   a new wrap function called __wrap_cxl_setup_parent_dport() on cxl_test
>   side, the function will filter all emulated dports, make sure only
>   real dports can be handled by cxl_setup_parent_dport().
>   (Patch 2)
> 
> v1 link: https://lore.kernel.org/linux-cxl/ZrHR+0w3bwM1Ik8h@xpf.sh.intel.com/T/#med6200e54ec12f09fdcc04571516adda261c9561
> 
> v2:
> - Add call trace log into changelog
> - Remove 'dev_is_platform(dport->dport_dev)' checking out of cxl driver
>   scope. Check if dport is emulated in cxl_test.

I am suprised we got this far without this being a problem earlier.

For the series you can add:

Reviewed-by: Dan Williams <dan.j.williams@intel.com>

...can you also follow along with a rename, documentation, and cleanup
patch?  cxl_setup_parent_dport() tells the reader absolutely nothing
about what the function does, and that it is specifically initializing
PCI AER operation.

It should be called something like cxl_dport_init_aer(), and it should
have kernel-doc associated with it. The cleanup opportunity I see is to
consolidate the ->native_aer check for the cxl_rcrb_to_aer() and
cxl_disable_rch_root_ints() into one location. It is a bit silly that
cxl_disable_rch_root_ints() needs to check if dport->regs.dport_aer was
initialized when it was just setup a few lines above. I.e. there are
just too many helper functions and it all could be consolidated in a
bigger cxl_dport_init_aer() function.

> 
> Li Ming (2):
>   cxl/pci: Get AER capability address from RCRB only for RCH dport
>   cxl/test: Skip cxl_setup_parent_dport() for emulated dports

This is the right thing to do whenever possible. The usage of
dev_is_platform() only makes sense for scenarios where a function is
called by the cxl_core that needs to avoid getting confused by cxl_test.

In this case, since cxl_mem is making the call to the exported
cxl_setup_parent_dport() symbol, then mocking it for cxl_test is
appropriate.