linux-kernel - Re: [RFC PATCH] tools/x86: add kcpuid tool to show raw CPU features

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 for Android: free password hash cracker in your pocket

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

Message-ID: <6afa8f68-4e88-ade1-fbe9-7cc7a0d2e42c@intel.com>
Date:   Wed, 2 Sep 2020 09:52:33 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     peterz@...radead.org, Feng Tang <feng.tang@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] tools/x86: add kcpuid tool to show raw CPU features

On 9/2/20 9:45 AM, peterz@...radead.org wrote:
> On Thu, Aug 27, 2020 at 03:49:03PM +0800, Feng Tang wrote:
>> End users frequently want to know what features their processor
>> supports, independent of what the kernel supports.
>>
>> /proc/cpuinfo is great. It is omnipresent and since it is provided by
>> the kernel it is always as up to date as the kernel. But, it can be
>> ambiguous about processor features which can be disabled by the kernel
>> at boot-time or compile-time.
> 
> Let me once again suggest we use CPUID faulting to 'fix' this.
> 
> We really should clear the CPUID bits when the kernel explicitly
> disables things.
> 
> https://lkml.kernel.org/r/1552431636-31511-18-git-send-email-fenghua.yu@intel.com

Wouldn't we also have to turn on faulting for all the bits that are
enumerated, but of which the kernel is unaware?

Right now, a bit that we clearcpuid= and one about which the kernel is
totally unaware look the same.