From: Borislav Petkov <bp@alien8.de>
To: peterz@infradead.org
Cc: Feng Tang <feng.tang@intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H . Peter Anvin" <hpa@zytor.com>,
Dave Hansen <dave.hansen@intel.com>,
x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH] tools/x86: add kcpuid tool to show raw CPU features
Date: Wed, 2 Sep 2020 18:55:01 +0200 [thread overview]
Message-ID: <20200902165501.GC21537@zn.tnic> (raw)
In-Reply-To: <20200902164538.GN1362448@hirez.programming.kicks-ass.net>
On Wed, Sep 02, 2020 at 06:45:38PM +0200, peterz@infradead.org wrote:
> We really should clear the CPUID bits when the kernel explicitly
> disables things.
Actually, you want to *disable* the functionality behind it by clearing
a bit in CR4 - and yes, not all features have CR4 bits - so that
luserspace doesn't "probe" the existence of certain instructions.
Example: you can still try to run RDRAND and succeed even if the
corresponding CPUID bit is clear.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2020-09-02 16:55 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-27 7:49 [RFC PATCH] tools/x86: add kcpuid tool to show raw CPU features Feng Tang
2020-09-02 15:40 ` Borislav Petkov
2020-09-02 16:25 ` Dave Hansen
2020-09-02 16:52 ` Borislav Petkov
2020-09-02 17:18 ` Dave Hansen
2020-09-02 18:19 ` Borislav Petkov
2020-09-03 7:17 ` Feng Tang
2020-09-02 16:45 ` peterz
2020-09-02 16:52 ` Dave Hansen
2020-09-02 16:59 ` peterz
2020-09-02 16:55 ` Borislav Petkov [this message]
2020-09-02 17:01 ` peterz
-- strict thread matches above, loose matches on Subject: below --
2020-07-21 2:00 Feng Tang
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