linux-kernel - Re: [PATCH] x86/tdx: Fix data leak in mmio

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Message-ID: <7401a060-884a-4e7f-9d87-10f5c5ac754d@intel.com>
Date: Mon, 26 Aug 2024 09:41:49 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>
Cc: linux-kernel@...r.kernel.org, linux-coco@...ts.linux.dev,
 Sean Christopherson <seanjc@...gle.com>, stable@...r.kernel.org
Subject: Re: [PATCH] x86/tdx: Fix data leak in mmio_read()

On 8/26/24 05:53, Kirill A. Shutemov wrote:
> The mmio_read() function makes a TDVMCALL to retrieve MMIO data for an
> address from the VMM.
> 
> Sean noticed that mmio_read() unintentionally exposes the value of an
> initialized variable on the stack to the VMM.
> 
> Do not send the original value of *val to the VMM.

The key to this is that 'val' is only used for the _return_ value, right?