linux-kernel - [tip: x86/tdx] x86/tdx: Zero out the missing RSI in TDX

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Date:   Tue, 12 Sep 2023 15:32:04 -0000
From:   "tip-bot2 for Kai Huang" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Kai Huang <kai.huang@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/tdx] x86/tdx: Zero out the missing RSI in TDX_HYPERCALL macro

The following commit has been merged into the x86/tdx branch of tip:

Commit-ID:     5d092b66119d774853cc9308522620299048a662
Gitweb:        https://git.kernel.org/tip/5d092b66119d774853cc9308522620299048a662
Author:        Kai Huang <kai.huang@...el.com>
AuthorDate:    Tue, 15 Aug 2023 23:01:55 +12:00
Committer:     Dave Hansen <dave.hansen@...ux.intel.com>
CommitterDate: Mon, 11 Sep 2023 16:31:52 -07:00

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.

Fixes: 7a3a401874be ("x86/tdx: Drop flags from __tdx_hypercall()")
Signed-off-by: Kai Huang <kai.huang@...el.com>
Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
Reviewed-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lore.kernel.org/all/e7d1157074a0b45d34564d5f17f3e0ffee8115e9.1692096753.git.kai.huang%40intel.com
---
 arch/x86/coco/tdx/tdcall.S | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/coco/tdx/tdcall.S b/arch/x86/coco/tdx/tdcall.S
index b193c0a..2eca5f4 100644
--- a/arch/x86/coco/tdx/tdcall.S
+++ b/arch/x86/coco/tdx/tdcall.S
@@ -195,6 +195,7 @@ SYM_FUNC_END(__tdx_module_call)
 	xor %r10d, %r10d
 	xor %r11d, %r11d
 	xor %rdi,  %rdi
+	xor %rsi,  %rsi
 	xor %rdx,  %rdx

 	/* Restore callee-saved GPRs as mandated by the x86_64 ABI */