linux-kernel - Re: Litmus test for question from Al Viro

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: <20201003132212.GB318272@rowland.harvard.edu>
Date:   Sat, 3 Oct 2020 09:22:12 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     parri.andrea@...il.com, will@...nel.org, peterz@...radead.org,
        boqun.feng@...il.com, npiggin@...il.com, dhowells@...hat.com,
        j.alglave@....ac.uk, luc.maranget@...ia.fr, akiyks@...il.com,
        dlustig@...dia.com, joel@...lfernandes.org,
        viro@...iv.linux.org.uk, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org
Subject: Re: Litmus test for question from Al Viro

To expand on my statement about the LKMM's weakness regarding control 
constructs, here is a litmus test to illustrate the issue.  You might 
want to add this to one of the archives.

Alan

C crypto-control-data
(*
 * LB plus crypto-control-data plus data
 *
 * Expected result: allowed
 *
 * This is an example of OOTA and we would like it to be forbidden.
 * The WRITE_ONCE in P0 is both data-dependent and (at the hardware level)
 * control-dependent on the preceding READ_ONCE.  But the dependencies are
 * hidden by the form of the conditional control construct, hence the 
 * name "crypto-control-data".  The memory model doesn't recognize them.
 *)

{}

P0(int *x, int *y)
{
	int r1;

	r1 = 1;
	if (READ_ONCE(*x) == 0)
		r1 = 0;
	WRITE_ONCE(*y, r1);
}

P1(int *x, int *y)
{
	WRITE_ONCE(*x, READ_ONCE(*y));
}

exists (0:r1=1)