linux-kernel - Re: [PATCH 3/3] x86/sev: The code for returning to user space is also in syscall gap

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Date:   Fri, 17 Dec 2021 12:00:34 +0100
From:   Joerg Roedel <jroedel@...e.de>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Lai Jiangshan <laijs@...ux.alibaba.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, Oleg Nesterov <oleg@...hat.com>,
        "Chang S. Bae" <chang.seok.bae@...el.com>,
        Jan Kiszka <jan.kiszka@...mens.com>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [PATCH 3/3] x86/sev: The code for returning to user space is
 also in syscall gap

On Fri, Dec 17, 2021 at 11:30:10AM +0100, Borislav Petkov wrote:
> I audited the handful instructions in there and didn't find anything
> that would cause a #VC...

If the hypervisor decides to mess with the code-page for this path
while a CPU is executing it. This will cause a #VC on that CPU and that
could hit in the syscall return path.

Regards,

-- 
Jörg Rödel
jroedel@...e.de

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