CVE-2024-53214

In the Linux kernel, the following vulnerability has been resolved:

vfio/pci: Properly hide first-in-list PCIe extended capability

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

A low impact flaw was found in the VFIO PCI subsystem of the Linux kernel as shipped in Red Hat Enterprise Linux 9. When the first entry in a PCI device's PCIe extended capability list is an unknown capability (a capability ID greater than PCI_EXT_CAP_ID_MAX), the vfio/pci driver does not hide it properly: the capability ID recorded in vfio_pci_core_device->pci_config_map is not re-checked in vfio_config_do_rw(), so a local privileged user reading the virtualized PCI configuration space of such a device through VFIO triggers a kernel WARNING and an out-of-bounds access to the ecap_perms array. Red Hat rates this flaw as low severity because exploiting it requires local privileges and access to a VFIO-managed device whose extended capability list begins with an unknown capability, and the practical consequence is limited to kernel availability (Red Hat CVSS 5.5, CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H). This is lower than the 7.8 score assigned by NIST, CISA, and the CVE record (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H), which assumes confidentiality and integrity impact that Red Hat's analysis of this out-of-bounds read of a kernel permissions array does not support. The fix is deferred for the affected RHEL 9 kernel and kernel-rt streams because of the low severity and the narrow conditions required to trigger the issue; the residual risk is a local denial of service limited to systems that expose affected devices through VFIO. Red Hat Enterprise Linux 6 is not affected, and the RHEL 7 and RHEL 8 streams are out of support scope.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.