tree ebf94b64f188e94c42997ac368cc8cd653ac3d68
parent 980a58a94dad539ff118cb9346b7ec1795afc537
author Kirill A. Shutemov <kirill.shutemov@linux.intel.com> 1666966340 +0300
committer Dave Hansen <dave.hansen@linux.intel.com> 1666999548 -0700

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() ]

Fixes: 9a22bf6debbf ("x86/traps: Add #VE support for TDX guest")
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/all/20221028141220.29217-3-kirill.shutemov%40linux.intel.com