On Tue, 11 Nov 2025 09:35:31 -0800 Alex Mastro <[email protected]> wrote:
> On Tue, Nov 11, 2025 at 10:09:48AM -0700, Alex Williamson wrote: > > On Tue, 11 Nov 2025 06:52:02 -0800 > > Alex Mastro <[email protected]> wrote: > > > diff --git a/tools/testing/selftests/vfio/lib/vfio_pci_device.c > > > b/tools/testing/selftests/vfio/lib/vfio_pci_device.c > > > index a381fd253aa7..7a523e3f2dce 100644 > > > --- a/tools/testing/selftests/vfio/lib/vfio_pci_device.c > > > +++ b/tools/testing/selftests/vfio/lib/vfio_pci_device.c > > > @@ -29,6 +29,173 @@ > > > VFIO_ASSERT_EQ(__ret, 0, "ioctl(%s, %s, %s) returned %d\n", #_fd, #_op, > > > #_arg, __ret); \ > > > } while (0) > > > > > > +static struct vfio_info_cap_header *next_cap_hdr(void *buf, size_t bufsz, > > > + size_t *cap_offset) > > > +{ > > > + struct vfio_info_cap_header *hdr; > > > + > > > + if (!*cap_offset) > > > + return NULL; > > > + > > > + VFIO_ASSERT_LT(*cap_offset, bufsz); > > > + VFIO_ASSERT_GE(bufsz - *cap_offset, sizeof(*hdr)); > > > + > > > + hdr = (struct vfio_info_cap_header *)((u8 *)buf + *cap_offset); > > > + > > > + if (hdr->next) > > > + VFIO_ASSERT_GT(hdr->next, *cap_offset); > > > > This might be implementation, but I don't think it's a requirement. > > The vfio capability chains are based on PCI capabilities, which have no > > ordering requirement. Thanks, > > My main interest was to enforce that the chain doesn't contain a cycle, and > checking for monotonically increasing cap offset was the simplest way I could > think of to guarantee such. > > If there isn't such a check, and kernel vends a malformed cycle-containing > chain, chain traversal would infinite loop. > > Given the location of this test code coupled to the kernel tree, do you think > such assumptions about implementation still reach too far? If yes, I can > either > remove this check, or try to make cycle detection more relaxed about offsets > potentially going backwards. I've seen cycle detection in PCI config space implemented as just a depth/ttl counter. Max cycles is roughly (buffer-size/header-size). I think that would be sufficient if we want to include that sanity testing. Thanks, Alex
