| Message ID | 20241124142739.21698-1-avihaih@nvidia.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v3] vfio/pci: Properly hide first-in-list PCIe extended capability | expand |
On Sun, 24 Nov 2024 16:27:39 +0200 Avihai Horon <avihaih@nvidia.com> wrote: > There are cases where a PCIe extended capability should be hidden from > the user. For example, an unknown capability (i.e., capability with ID > greater than PCI_EXT_CAP_ID_MAX) or a capability that is intentionally > chosen to be hidden from the user. > > Hiding a capability is done by virtualizing and modifying the 'Next > Capability Offset' field of the previous capability so it points to the > capability after the one that should be hidden. > > The special case where the first capability in the list should be hidden > is handled differently because there is no previous capability that can > be modified. In this case, the capability ID and version are zeroed > while leaving the next pointer intact. This hides the capability and > leaves an anchor for the rest of the capability list. > > However, today, hiding the first capability in the list is not done > properly if the capability is unknown, as struct > vfio_pci_core_device->pci_config_map is set to the capability ID during > initialization but the capability ID is not properly checked later when > used in vfio_config_do_rw(). This leads to the following warning [1] and > to an out-of-bounds access to ecap_perms array. > > Fix it by checking cap_id in vfio_config_do_rw(), and if it is greater > than PCI_EXT_CAP_ID_MAX, use an alternative struct perm_bits for direct > read only access instead of the ecap_perms array. > > Note that this is safe since the above is the only case where cap_id can > exceed PCI_EXT_CAP_ID_MAX (except for the special capabilities, which > are already checked before). > > [1] > > WARNING: CPU: 118 PID: 5329 at drivers/vfio/pci/vfio_pci_config.c:1900 vfio_pci_config_rw+0x395/0x430 [vfio_pci_core] > CPU: 118 UID: 0 PID: 5329 Comm: simx-qemu-syste Not tainted 6.12.0+ #1 > (snip) > Call Trace: > <TASK> > ? show_regs+0x69/0x80 > ? __warn+0x8d/0x140 > ? vfio_pci_config_rw+0x395/0x430 [vfio_pci_core] > ? report_bug+0x18f/0x1a0 > ? handle_bug+0x63/0xa0 > ? exc_invalid_op+0x19/0x70 > ? asm_exc_invalid_op+0x1b/0x20 > ? vfio_pci_config_rw+0x395/0x430 [vfio_pci_core] > ? vfio_pci_config_rw+0x244/0x430 [vfio_pci_core] > vfio_pci_rw+0x101/0x1b0 [vfio_pci_core] > vfio_pci_core_read+0x1d/0x30 [vfio_pci_core] > vfio_device_fops_read+0x27/0x40 [vfio] > vfs_read+0xbd/0x340 > ? vfio_device_fops_unl_ioctl+0xbb/0x740 [vfio] > ? __rseq_handle_notify_resume+0xa4/0x4b0 > __x64_sys_pread64+0x96/0xc0 > x64_sys_call+0x1c3d/0x20d0 > do_syscall_64+0x4d/0x120 > entry_SYSCALL_64_after_hwframe+0x76/0x7e > > Fixes: 89e1f7d4c66d ("vfio: Add PCI device driver") > Signed-off-by: Avihai Horon <avihaih@nvidia.com> > Reviewed-by: Yi Liu <yi.l.liu@intel.com> > Tested-by: Yi Liu <yi.l.liu@intel.com> > --- > Changes from v2: > * Fix clang compilation error reported by kernel test robot. > * Drop const qualifier of direct_ro_perms to avoid casting in > vfio_config_do_rw and to be aligned with other perms declaration. > * Add Yi's R-b/T-b tags. Applied to vfio next branch for v6.13. Thanks, Alex > Changes from v1: > * Use Alex's suggestion to fix the bug and adapt the commit message. > --- > drivers/vfio/pci/vfio_pci_config.c | 16 ++++++++++++++-- > 1 file changed, 14 insertions(+), 2 deletions(-) > > diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c > index 97422aafaa7b..ea2745c1ac5e 100644 > --- a/drivers/vfio/pci/vfio_pci_config.c > +++ b/drivers/vfio/pci/vfio_pci_config.c > @@ -313,6 +313,10 @@ static int vfio_virt_config_read(struct vfio_pci_core_device *vdev, int pos, > return count; > } > > +static struct perm_bits direct_ro_perms = { > + .readfn = vfio_direct_config_read, > +}; > + > /* Default capability regions to read-only, no-virtualization */ > static struct perm_bits cap_perms[PCI_CAP_ID_MAX + 1] = { > [0 ... PCI_CAP_ID_MAX] = { .readfn = vfio_direct_config_read } > @@ -1897,9 +1901,17 @@ static ssize_t vfio_config_do_rw(struct vfio_pci_core_device *vdev, char __user > cap_start = *ppos; > } else { > if (*ppos >= PCI_CFG_SPACE_SIZE) { > - WARN_ON(cap_id > PCI_EXT_CAP_ID_MAX); > + /* > + * We can get a cap_id that exceeds PCI_EXT_CAP_ID_MAX > + * if we're hiding an unknown capability at the start > + * of the extended capability list. Use default, ro > + * access, which will virtualize the id and next values. > + */ > + if (cap_id > PCI_EXT_CAP_ID_MAX) > + perm = &direct_ro_perms; > + else > + perm = &ecap_perms[cap_id]; > > - perm = &ecap_perms[cap_id]; > cap_start = vfio_find_cap_start(vdev, *ppos); > } else { > WARN_ON(cap_id > PCI_CAP_ID_MAX);
diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c index 97422aafaa7b..ea2745c1ac5e 100644 --- a/drivers/vfio/pci/vfio_pci_config.c +++ b/drivers/vfio/pci/vfio_pci_config.c @@ -313,6 +313,10 @@ static int vfio_virt_config_read(struct vfio_pci_core_device *vdev, int pos, return count; } +static struct perm_bits direct_ro_perms = { + .readfn = vfio_direct_config_read, +}; + /* Default capability regions to read-only, no-virtualization */ static struct perm_bits cap_perms[PCI_CAP_ID_MAX + 1] = { [0 ... PCI_CAP_ID_MAX] = { .readfn = vfio_direct_config_read } @@ -1897,9 +1901,17 @@ static ssize_t vfio_config_do_rw(struct vfio_pci_core_device *vdev, char __user cap_start = *ppos; } else { if (*ppos >= PCI_CFG_SPACE_SIZE) { - WARN_ON(cap_id > PCI_EXT_CAP_ID_MAX); + /* + * We can get a cap_id that exceeds PCI_EXT_CAP_ID_MAX + * if we're hiding an unknown capability at the start + * of the extended capability list. Use default, ro + * access, which will virtualize the id and next values. + */ + if (cap_id > PCI_EXT_CAP_ID_MAX) + perm = &direct_ro_perms; + else + perm = &ecap_perms[cap_id]; - perm = &ecap_perms[cap_id]; cap_start = vfio_find_cap_start(vdev, *ppos); } else { WARN_ON(cap_id > PCI_CAP_ID_MAX);
There are cases where a PCIe extended capability should be hidden from the user. For example, an unknown capability (i.e., capability with ID greater than PCI_EXT_CAP_ID_MAX) or a capability that is intentionally chosen to be hidden from the user. Hiding a capability is done by virtualizing and modifying the 'Next Capability Offset' field of the previous capability so it points to the capability after the one that should be hidden. The special case where the first capability in the list should be hidden is handled differently because there is no previous capability that can be modified. In this case, the capability ID and version are zeroed while leaving the next pointer intact. This hides the capability and leaves an anchor for the rest of the capability list. However, today, hiding the first capability in the list is not done properly if the capability is unknown, as struct vfio_pci_core_device->pci_config_map is set to the capability ID during initialization but the capability ID is not properly checked later when used in vfio_config_do_rw(). This leads to the following warning [1] and to an out-of-bounds access to ecap_perms array. Fix it by checking cap_id in vfio_config_do_rw(), and if it is greater than PCI_EXT_CAP_ID_MAX, use an alternative struct perm_bits for direct read only access instead of the ecap_perms array. Note that this is safe since the above is the only case where cap_id can exceed PCI_EXT_CAP_ID_MAX (except for the special capabilities, which are already checked before). [1] WARNING: CPU: 118 PID: 5329 at drivers/vfio/pci/vfio_pci_config.c:1900 vfio_pci_config_rw+0x395/0x430 [vfio_pci_core] CPU: 118 UID: 0 PID: 5329 Comm: simx-qemu-syste Not tainted 6.12.0+ #1 (snip) Call Trace: <TASK> ? show_regs+0x69/0x80 ? __warn+0x8d/0x140 ? vfio_pci_config_rw+0x395/0x430 [vfio_pci_core] ? report_bug+0x18f/0x1a0 ? handle_bug+0x63/0xa0 ? exc_invalid_op+0x19/0x70 ? asm_exc_invalid_op+0x1b/0x20 ? vfio_pci_config_rw+0x395/0x430 [vfio_pci_core] ? vfio_pci_config_rw+0x244/0x430 [vfio_pci_core] vfio_pci_rw+0x101/0x1b0 [vfio_pci_core] vfio_pci_core_read+0x1d/0x30 [vfio_pci_core] vfio_device_fops_read+0x27/0x40 [vfio] vfs_read+0xbd/0x340 ? vfio_device_fops_unl_ioctl+0xbb/0x740 [vfio] ? __rseq_handle_notify_resume+0xa4/0x4b0 __x64_sys_pread64+0x96/0xc0 x64_sys_call+0x1c3d/0x20d0 do_syscall_64+0x4d/0x120 entry_SYSCALL_64_after_hwframe+0x76/0x7e Fixes: 89e1f7d4c66d ("vfio: Add PCI device driver") Signed-off-by: Avihai Horon <avihaih@nvidia.com> Reviewed-by: Yi Liu <yi.l.liu@intel.com> Tested-by: Yi Liu <yi.l.liu@intel.com> --- Changes from v2: * Fix clang compilation error reported by kernel test robot. * Drop const qualifier of direct_ro_perms to avoid casting in vfio_config_do_rw and to be aligned with other perms declaration. * Add Yi's R-b/T-b tags. Changes from v1: * Use Alex's suggestion to fix the bug and adapt the commit message. --- drivers/vfio/pci/vfio_pci_config.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-)