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. ]