Subject: CVE-2023-52874: x86/tdx: Zero out the missing RSI in TDX_HYPERCALL macro

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

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.

The Linux kernel CVE team has assigned CVE-2023-52874 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 6.4 with commit 7a3a401874be and fixed in 6.5.12 with commit 2191950d35d8
	Issue introduced in 6.4 with commit 7a3a401874be and fixed in 6.6.2 with commit de4c5bacca4f
	Issue introduced in 6.4 with commit 7a3a401874be and fixed in 6.7 with commit 5d092b66119d

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2023-52874
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	arch/x86/coco/tdx/tdcall.S

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/2191950d35d8f81620ea8d4e04d983f664fe3a8a
	https://git.kernel.org/stable/c/de4c5bacca4f50233f1f791bec9eeb4dee1b14cd
	https://git.kernel.org/stable/c/5d092b66119d774853cc9308522620299048a662