linux-kernel - Re: [PATCH v2 1/8] kcsan: Add Kernel Concurrency Sanitizer infrastructure

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: <20191022154858.GA13700@redhat.com>
Date:   Tue, 22 Oct 2019 17:48:58 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Marco Elver <elver@...gle.com>
Cc:     akiyks@...il.com, stern@...land.harvard.edu, glider@...gle.com,
        parri.andrea@...il.com, andreyknvl@...gle.com, luto@...nel.org,
        ard.biesheuvel@...aro.org, arnd@...db.de, boqun.feng@...il.com,
        bp@...en8.de, dja@...ens.net, dlustig@...dia.com,
        dave.hansen@...ux.intel.com, dhowells@...hat.com,
        dvyukov@...gle.com, hpa@...or.com, mingo@...hat.com,
        j.alglave@....ac.uk, joel@...lfernandes.org, corbet@....net,
        jpoimboe@...hat.com, luc.maranget@...ia.fr, mark.rutland@....com,
        npiggin@...il.com, paulmck@...ux.ibm.com, peterz@...radead.org,
        tglx@...utronix.de, will@...nel.org, kasan-dev@...glegroups.com,
        linux-arch@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-efi@...r.kernel.org, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org
Subject: Re: [PATCH v2 1/8] kcsan: Add Kernel Concurrency Sanitizer
 infrastructure

On 10/17, Marco Elver wrote:
>
> +	/*
> +	 * Delay this thread, to increase probability of observing a racy
> +	 * conflicting access.
> +	 */
> +	udelay(get_delay());
> +
> +	/*
> +	 * Re-read value, and check if it is as expected; if not, we infer a
> +	 * racy access.
> +	 */
> +	switch (size) {
> +	case 1:
> +		is_expected = expect_value._1 == READ_ONCE(*(const u8 *)ptr);
> +		break;
> +	case 2:
> +		is_expected = expect_value._2 == READ_ONCE(*(const u16 *)ptr);
> +		break;
> +	case 4:
> +		is_expected = expect_value._4 == READ_ONCE(*(const u32 *)ptr);
> +		break;
> +	case 8:
> +		is_expected = expect_value._8 == READ_ONCE(*(const u64 *)ptr);
> +		break;
> +	default:
> +		break; /* ignore; we do not diff the values */
> +	}
> +
> +	/* Check if this access raced with another. */
> +	if (!remove_watchpoint(watchpoint)) {
> +		/*
> +		 * No need to increment 'race' counter, as the racing thread
> +		 * already did.
> +		 */
> +		kcsan_report(ptr, size, is_write, smp_processor_id(),
> +			     kcsan_report_race_setup);
> +	} else if (!is_expected) {
> +		/* Inferring a race, since the value should not have changed. */
> +		kcsan_counter_inc(kcsan_counter_races_unknown_origin);
> +#ifdef CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN
> +		kcsan_report(ptr, size, is_write, smp_processor_id(),
> +			     kcsan_report_race_unknown_origin);
> +#endif
> +	}

Not sure I understand this code...

Just for example. Suppose that task->state = TASK_UNINTERRUPTIBLE, this task
does __set_current_state(TASK_RUNNING), another CPU does wake_up_process(task)
which does the same UNINTERRUPTIBLE -> RUNNING transition.

Looks like, this is the "data race" according to kcsan?

Hmm. even the "if (!(p->state & state))" check in try_to_wake_up() can trigger
kcsan_report() ?

Oleg.