CVE-2023-52874

In the Linux kernel, the following vulnerability has been resolved:
x86/tdx: Zero out the missing RSI in TDX_HYPERCALL macro In the
TDX_HYPERCALL asm, after the TDCALL instruction returns from the untrusted
VMM, the registers that the TDX guest shares to the VMM need to be cleared
to avoid speculative execution of VMM-provided values. RSI is specified in
the bitmap of those registers, but it is missing when zeroing out those
registers in the current TDX_HYPERCALL. It was there when it was originally
added in commit 752d13305c78 (“x86/tdx: Expand __tdx_hypercall() to handle
more arguments”), but was later removed in commit 1e70c680375a (“x86/tdx:
Do not corrupt frame-pointer in __tdx_hypercall()”), which was correct
because %rsi is later restored in the “pop %rsi”. However a later commit
7a3a401874be (“x86/tdx: Drop flags from __tdx_hypercall()”) removed that
“pop %rsi” but forgot to add the “xor %rsi, %rsi” back. Fix by adding it
back.