linux-kernel - Re: [PATCH 1/3] x86/cpu: Process all CPUID dependencies after identifying CPU info

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: <Y5IUsB83PzHCJ+EY@zn.tnic>
Date:   Thu, 8 Dec 2022 17:45:36 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH 1/3] x86/cpu: Process all CPUID dependencies after
 identifying CPU info

On Thu, Dec 08, 2022 at 04:26:29PM +0000, Sean Christopherson wrote:
> But it's not really a hardware issue either.  More like an admin/user issue.
> 
> The problem is that if a kernel is built for subset of CPU types, e.g. just Intel
> or just Centaur, and then booted on an "unsupported" CPU type, init_ia32_feat_ctl()
> will never be invoked because ->c_init() will point a default_init(), and so the
> kernel never checks MSR_IA32_FEAT_CTL to see if VMX and/or SGX are fully enabled.

Yeah, you called it an "edge case". I'm wondering whether we should even
worry about that case...

I mean, the majority of Linuxes out there are allmodconfig-like kernels
and booting on unsupported CPU type doesn't happen.

Hell, I'd even say that if you attempt booting on unsupported CPU type,
we should simply fail that boot attempt.

I.e., what validate_cpu() does in some cases.

IOW, I don't mind what you're doing but I wonder whether we should even
go the trouble to do so or simply deny that by saying "Well, don't do
that then".

Hmmm.

-- 
Regards/Gruss,
    Boris.

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