linux-kernel - Re: [PATCH -v2] x86/CPU/AMD: Make sure EFER[AIBRSE] is set

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Date:   Mon, 13 Mar 2023 08:42:11 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Josh Poimboeuf <jpoimboe@...nel.org>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Kim Phillips <kim.phillips@....com>, x86@...nel.org,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Joao Martins <joao.m.martins@...cle.com>,
        Jonathan Corbet <corbet@....net>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Juergen Gross <jgross@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tony Luck <tony.luck@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Alexey Kardashevskiy <aik@....com>, kvm@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -v2] x86/CPU/AMD: Make sure EFER[AIBRSE] is set

On 3/10/23 08:22, Borislav Petkov wrote:
> The AutoIBRS bit gets set only on the BSP as part of determining which
> mitigation to enable on AMD. Setting on the APs relies on the
> circumstance that the APs get booted through the trampoline and EFER
> - the MSR which contains that bit - gets replicated on every AP from the
> BSP.
> 
> However, this can change in the future and considering the security
> implications of this bit not being set on every CPU, make sure it is set
> by verifying EFER later in the boot process and on every AP.
> 
> Reported-by: Josh Poimboeuf <jpoimboe@...nel.org>
> Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
> Link: https://lore.kernel.org/r/20230224185257.o3mcmloei5zqu7wa@treble

Looks sane, thanks for adding the warning:

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