CVE-2022-49886

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

x86/tdx: Panic on bad configs that #VE on "private" memory access

All normal kernel memory is "TDX private memory". This includes everything from kernel stacks to kernel text. Handling exceptions on arbitrary accesses to kernel memory is essentially impossible because they can happen in horribly nasty places like kernel entry/exit. But, TDX hardware can theoretically deliver a virtualization exception (#VE) on any access to private memory.

But, it's not as bad as it sounds. TDX can be configured to never deliver these exceptions on private memory with a "TD attribute" called ATTR_SEPT_VE_DISABLE. The guest has no way to set this attribute, but it can check it.

Ensure ATTR_SEPT_VE_DISABLE is set in early boot. panic() if it is unset. There is no sane way for Linux to run with this attribute clear so a panic() is appropriate.

There's small window during boot before the check where kernel has an early #VE handler. But the handler is only for port I/O and will also panic() as soon as it sees any other #VE, such as a one generated by a private memory access.

[ dhansen: Rewrite changelog and rebase on new tdx_parse_tdinfo(). Add Kirill's tested-by because I made changes since he wrote this. ]

Only affects guest systems running on TDX hardware. The Linux kernel now explicitly checks that the TDX attribute ATTR_SEPT_VE_DISABLE is set, ensuring no virtualization exceptions (#VE) are delivered for accesses to private kernel memory. Without this attribute, the TDX guest could panic during normal memory operations, making the system unbootable or unstable, though it does not enable privilege escalation or memory corruption. The vulnerability fixed in Red Hat Enterprise Linux 9 (all versions) and fixed for the Red Hat Enterprise Linux 8 starting from 8.8 version.

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.