linux-kernel - Re: [PATCH] x86/sev-es: Fix SEV-ES #VC handler for string port IO

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Date:   Fri, 8 Jan 2021 18:20:49 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "Hyunwook (Wooky) Baek" <baekhw@...gle.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        David Rientjes <rientjes@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH] x86/sev-es: Fix SEV-ES #VC handler for string port IO

On Thu, Jan 07, 2021 at 06:51:07PM -0800, Hyunwook (Wooky) Baek wrote:
> Don't assume dest/source buffers are userspace addresses when manually
> copying data for string I/O or MOVS MMIO, as {get,put}_user() will fail
> if handed a kernel address and ultimately lead to a kernel panic.
> 
> Signed-off-by: Hyunwook (Wooky) Baek <baekhw@...gle.com>
> Acked-by: David Rientjes <rientjes@...gle.com>
> ---
>  arch/x86/kernel/sev-es.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
> index 0bd1a0fc587e..812494d216ba 100644
> --- a/arch/x86/kernel/sev-es.c
> +++ b/arch/x86/kernel/sev-es.c
> @@ -286,6 +286,12 @@ static enum es_result vc_write_mem(struct es_em_ctxt *ctxt,
>  	u16 d2;
>  	u8  d1;
>  
> +	/* If instruction ran in kernel mode and the I/O buffer is in kernel space */
> +	if (!user_mode(ctxt->regs) && !access_ok(s, size)) {
						^^^

Just by looking at this patch I know you haven't tested it before sending.

:-(

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette