linux-kernel - RE: [PATCH v10 6/6] x86/split_lock: Enable split lock detection by kernel parameter

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: Windows password security audit tool. GUI, reports in PDF.

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

Message-ID: <3908561D78D1C84285E8C5FCA982C28F7F4DD19F@ORSMSX115.amr.corp.intel.com>
Date:   Fri, 22 Nov 2019 17:48:14 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>
CC:     "Yu, Fenghua" <fenghua.yu@...el.com>,
        David Laight <David.Laight@...lab.com>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        H Peter Anvin <hpa@...or.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        x86 <x86@...nel.org>, "Will Deacon" <will@...nel.org>
Subject: RE: [PATCH v10 6/6] x86/split_lock: Enable split lock detection by
 kernel parameter

> When we use byte ops, we must consider the word as 4 independent
> variables. And in that case the later load might observe the lock-byte
> state from 3, because the modification to the lock byte from 4 is in
> CPU2's store-buffer.

So we absolutely violate this with the optimization for constant arguments
to set_bit(), clear_bit() and change_bit() that are implemented as byte ops.

So is code that does:

	set_bit(0, bitmap);

on one CPU. While another is doing:

	set_bit(mybit, bitmap);

on another CPU safe? The first operates on just one byte, the second  on 8 bytes.

-Tony