linux-kernel - Re: [PATCH v6 0/6] x86/tdx: Allow MMIO instructions from userspace

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <6c158a14-ba01-4146-9c6c-8e4c035dd055@intel.com>
Date: Fri, 6 Sep 2024 09:19:28 -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, Sean Christopherson <seanjc@...gle.com>,
 Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v6 0/6] x86/tdx: Allow MMIO instructions from userspace

On 9/6/24 04:49, Alexey Gladkov wrote:
> Currently, MMIO inside the TDX guest is allowed from kernel space and access
> from userspace is denied. This becomes a problem when working with virtual
> devices in userspace.

Kernel MMIO and User MMIO are very different beasts.

The kernel MMIO instructions are trusted and can be constrained to use a
very limited number of instructions that match the kernel's limited
instruction decoding capability.

Userspace is not constrained in that way.

TDX also doesn't have the option of having the VMM deal with the
instruction emulation.

Before we start down this road, I'd really want to hear from the KVM
folks that having the kernel decode arbitrary user instructions is the
way we want to go.