linux-kernel - How is Code in do_sys_settimeofday() safe in case of SMP and Nest Kernel Path?

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-next>] [day] [month] [year] [list]

Message-ID: <a2ebde260609290733m207780f0t8601e04fcf64f0a6@mail.gmail.com>
Date:	Fri, 29 Sep 2006 22:33:54 +0800
From:	"Dong Feng" <middle.fengdong@...il.com>
To:	"Andi Kleen" <ak@...e.de>, "Nick Piggin" <nickpiggin@...oo.com.au>,
	"Arjan van de Ven" <arjan@...radead.org>,
	"Dong Feng" <middle.fengdong@...il.com>,
	"Paul Mackerras" <paulus@...ba.org>,
	"Christoph Lameter" <clameter@....com>,
	"David Howells" <dhowells@...hat.com>
Cc:	linux-kernel@...r.kernel.org
Subject: How is Code in do_sys_settimeofday() safe in case of SMP and Nest Kernel Path?

Hi, all,

I got a question, that is, I am confused by the following code in
do_sys_settimeofday().

if (tz) {
    /* SMP safe, global irq locking makes it work. */
        sys_tz = *tz;
        if (firsttime) {
            firsttime = 0;
            if (!tv)
                warp_clock();
    }
}

For my understanding, an assignment between structs should be a
bit-wise copy. Such operation is not atomic, so it can not be supposed
SMP-safe. And the subsequent test-and-assign operation on firsttime is
not atomic, either.

If the comments mean the subsequent code is SMP-safe and can prevent
nest-kernel-path, how does it achieves that?

Thank you in advance.
Feng,Dong
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/