linux-kernel - Re: [PATCH v6 1/6] x86/tdx: Fix "in-kernel MMIO" check

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Message-ID: <gwxxb4o64g5e3ulihhv6aar3m3btkza4vt7gjplx4lvylegd65@vm3sjh243oek>
Date: Tue, 10 Sep 2024 22:59:10 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Alexey Gladkov <legion@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-coco@...ts.linux.dev, 
	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>, 
	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 v6 1/6] x86/tdx: Fix "in-kernel MMIO" check

On Fri, Sep 06, 2024 at 01:49:59PM +0200, Alexey Gladkov wrote:
> From: "Alexey Gladkov (Intel)" <legion@...nel.org>
> 
> 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.
> 
> Cc: stable@...r.kernel.org
> Signed-off-by: Alexey Gladkov (Intel) <legion@...nel.org>

Reviewed-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

-- 
  Kiryl Shutsemau / Kirill A. Shutemov