linux-kernel - Re: [PATCH] x86/srso: Correct the mitigation status when SMT is disabled

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Message-ID: <20230816182940.xw67h5xbilqpb5au@treble>
Date:   Wed, 16 Aug 2023 11:29:40 -0700
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Nikolay Borisov <nik.borisov@...e.com>, X86 ML <x86@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/srso: Correct the mitigation status when SMT is
 disabled

On Wed, Aug 16, 2023 at 07:35:31PM +0200, Borislav Petkov wrote:
> On Wed, Aug 16, 2023 at 09:07:57AM -0700, Josh Poimboeuf wrote:
> > In this case srso_show_state() is never called, so the following code
> > can't run:
> > 
> > +	if (boot_cpu_has(X86_FEATURE_SRSO_NO)) {
> > +		if (sched_smt_active())
> > +			return sysfs_emit(buf, "Not affected\n");
> 
> Ofc it can. If something has set X86_FEATURE_SRSO_NO early, before the
> bug bits detection happens, then you get:
> 
> $ cat /sys/devices/system/cpu/vulnerabilities/spec_rstack_overflow
> Not affected

No, if the bug bit isn't set then that comes from cpu_show_common():

static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr,
			       char *buf, unsigned int bug)
{
	if (!boot_cpu_has_bug(bug))
		return sysfs_emit(buf, "Not affected\n");

-- 
Josh