linux-kernel - Re: [patch 08/41] x86/fpu: Restrict fpstate sanitizing to legacy components

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Message-ID: <87r1h7usuf.ffs@nanos.tec.linutronix.de>
Date:   Sat, 12 Jun 2021 15:15:36 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Andy Lutomirski <luto@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Borislav Petkov <bp@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Kan Liang <kan.liang@...ux.intel.com>
Subject: Re: [patch 08/41] x86/fpu: Restrict fpstate sanitizing to legacy components

On Sat, Jun 12 2021 at 00:12, Thomas Gleixner wrote:
> On Fri, Jun 11 2021 at 12:03, Andy Lutomirski wrote:
>> On 6/11/21 9:15 AM, Thomas Gleixner wrote:
>>> + *
>>> + * This is required for the legacy regset functions.
>>> + */
>>> +static void fpstate_sanitize_legacy(struct fpu *fpu)
>>> +{
>>> +	struct fxregs_state *fx = &fpu->state.fxsave;
>>> +	u64 xfeatures;
>>> +
>>> +	if (!use_xsaveopt())
>>> +		return;
>>
>> This is confusing, since we never use xsaveopt.  It's also wrong -- see
>> above.  How about just removing it?
>
> We do and this code is buggy because xsaves does not clear the component
> storage either. Neither does xsavec which we in fact do not use in the
> kernel.

So that kinda works because the CPUs which have XSAVES have XSAVEOPT
too. But XSAVESOPT can be disabled on the command line, which then makes
that condition false...

Oh well.