linux-kernel - RE: [patch v2 1/2] x86,module: Detect VMX modules and disable Split-Lock-Detect

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Message-ID: <9b95fe9e81c14370859e19f081cc23e4@AcuMS.aculab.com>
Date:   Fri, 3 Apr 2020 08:09:03 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Peter Zijlstra' <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>
CC:     LKML <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "Kenneth R. Crudup" <kenny@...ix.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jessica Yu <jeyu@...nel.org>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Xiaoyao Li <xiaoyao.li@...el.com>,
        Nadav Amit <namit@...are.com>,
        Thomas Hellstrom <thellstrom@...are.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        "Steven Rostedt" <rostedt@...dmis.org>
Subject: RE: [patch v2 1/2] x86,module: Detect VMX modules and disable
 Split-Lock-Detect

From: Peter Zijlstra
> Sent: 02 April 2020 16:24
> 
> I picked VMXOFF (which also appears in vmmon.ko) instead of VMXON
> because that latter takes an argument is therefore more difficult to
> decode.
...
> +	while (text < text_end) {
> +		kernel_insn_init(&insn, text, text_end - text);
> +		insn_get_length(&insn);
> +
> +		if (WARN_ON_ONCE(!insn_complete(&insn)))
> +			break;
> +
> +		if (insn.length == 3 &&
> +		    (!memcmp(text, vmlaunch, sizeof(vmlaunch)) ||
> +		     !memcmp(text, vmxoff, sizeof(vmxoff))))
> +				goto bad_module;
> +
> +		text += insn.length;
> +	}

How long is that going to take on a module with (say) 400k of text?

	David

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