Re: [PATCH] x86/kvm/tdx: Save %rbp in TDX_MODULE_CALL

Kirill A. Shutemov
2024-05-17T13:55:53Z

On Fri, May 17, 2024 at 02:14:50PM +0200, Juergen Gross wrote:
> While testing TDX host support patches, a crash of the host has been
> observed a few instructions after doing a seamcall. Reason was a
> clobbered %rbp (set to 0), which occurred in spite of the TDX module
> offering the feature NOT to modify %rbp across TDX module calls.
>
> In order not having to build the host kernel with CONFIG_FRAME_POINTER,
> save %rbp across a seamcall/tdcall.

There's a feature in TDX module 1.5 that prevents RBP modification across
TDH.VP.ENTER SEAMCALL. See NO_RBP_MOD in TDX Module 1.5 ABI spec.

I think it has to be enabled for all TDs and TDX modules that don't
support it need to be rejected.

--
Kiryl Shutsemau / Kirill A. Shutemov