linux-kernel - Re: [PATCH v7 1/6] x86/tdx: Fix "in-kernel MMIO" check

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Message-ID: <385cb72c-1220-484a-80db-9f5aeeca8484@intel.com>
Date: Fri, 13 Sep 2024 10:18:14 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Alexey Gladkov <legion@...nel.org>, linux-kernel@...r.kernel.org,
 linux-coco@...ts.linux.dev
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 "H. Peter Anvin" <hpa@...or.com>,
 "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
 Andrew Morton <akpm@...ux-foundation.org>, Yuan Yao <yuan.yao@...el.com>,
 Geert Uytterhoeven <geert@...ux-m68k.org>, Yuntao Wang <ytcoode@...il.com>,
 Kai Huang <kai.huang@...el.com>, Baoquan He <bhe@...hat.com>,
 Oleg Nesterov <oleg@...hat.com>, cho@...rosoft.com, decui@...rosoft.com,
 John.Starks@...rosoft.com, stable@...r.kernel.org
Subject: Re: [PATCH v7 1/6] x86/tdx: Fix "in-kernel MMIO" check

On 9/13/24 10:05, Alexey Gladkov wrote:
> TDX only supports kernel-initiated MMIO operations. The handle_mmio()
> function checks if the #VE exception occurred in the kernel and rejects
> the operation if it did not.
> 
> However, userspace can deceive the kernel into performing MMIO on its
> behalf. For example, if userspace can point a syscall to an MMIO address,
> syscall does get_user() or put_user() on it, triggering MMIO #VE. The
> kernel will treat the #VE as in-kernel MMIO.
> 
> Ensure that the target MMIO address is within the kernel before decoding
> instruction.

Acked-by: Dave Hansen <dave.hansen@...ux.intel.com>