linux-kernel - Re: [PATCH v2 01/14] kasan: sw_tags: Use arithmetic shift for shadow computation

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] [day] [month] [year] [list]

Message-ID: <b2bioloa3qsueqiyjadi5zsvi63v6zh3vwzji4ed4dmsxkaudb@hrxzs4vh7wjf>
Date: Fri, 14 Mar 2025 16:57:48 +0100
From: Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>
To: Andrey Konovalov <andreyknvl@...il.com>
CC: <kees@...nel.org>, <julian.stecklina@...erus-technology.de>,
	<kevinloughlin@...gle.com>, <peterz@...radead.org>, <tglx@...utronix.de>,
	<justinstitt@...gle.com>, <catalin.marinas@....com>,
	<wangkefeng.wang@...wei.com>, <bhe@...hat.com>, <ryabinin.a.a@...il.com>,
	<kirill.shutemov@...ux.intel.com>, <will@...nel.org>, <ardb@...nel.org>,
	<jason.andryuk@....com>, <dave.hansen@...ux.intel.com>,
	<pasha.tatashin@...een.com>, <guoweikang.kernel@...il.com>,
	<dwmw@...zon.co.uk>, <mark.rutland@....com>, <broonie@...nel.org>,
	<apopple@...dia.com>, <bp@...en8.de>, <rppt@...nel.org>,
	<kaleshsingh@...gle.com>, <richard.weiyang@...il.com>, <luto@...nel.org>,
	<glider@...gle.com>, <pankaj.gupta@....com>,
	<pawan.kumar.gupta@...ux.intel.com>, <kuan-ying.lee@...onical.com>,
	<tony.luck@...el.com>, <tj@...nel.org>, <jgross@...e.com>,
	<dvyukov@...gle.com>, <baohua@...nel.org>, <samuel.holland@...ive.com>,
	<dennis@...nel.org>, <akpm@...ux-foundation.org>,
	<thomas.weissschuh@...utronix.de>, <surenb@...gle.com>,
	<kbingham@...nel.org>, <ankita@...dia.com>, <nathan@...nel.org>,
	<ziy@...dia.com>, <xin@...or.com>, <rafael.j.wysocki@...el.com>,
	<andriy.shevchenko@...ux.intel.com>, <cl@...ux.com>, <jhubbard@...dia.com>,
	<hpa@...or.com>, <scott@...amperecomputing.com>, <david@...hat.com>,
	<jan.kiszka@...mens.com>, <vincenzo.frascino@....com>, <corbet@....net>,
	<maz@...nel.org>, <mingo@...hat.com>, <arnd@...db.de>, <ytcoode@...il.com>,
	<xur@...gle.com>, <morbo@...gle.com>, <thiago.bauermann@...aro.org>,
	<linux-doc@...r.kernel.org>, <kasan-dev@...glegroups.com>,
	<linux-kernel@...r.kernel.org>, <llvm@...ts.linux.dev>, <linux-mm@...ck.org>,
	<linux-arm-kernel@...ts.infradead.org>, <x86@...nel.org>
Subject: Re: [PATCH v2 01/14] kasan: sw_tags: Use arithmetic shift for shadow
 computation

On 2025-03-07 at 02:10:12 +0100, Andrey Konovalov wrote:
>On Tue, Mar 4, 2025 at 1:31 PM Maciej Wieczor-Retman
><maciej.wieczor-retman@...el.com> wrote:
>>
>> One other question that came to me about how KASAN works, is there some
>> mechanism to prevent data races between two threads? In the compiler perhaps?
>>
>> For example memory is de-allocated and shadow memory is poisoned but some other
>> thread was just about to do a shadow memory check and was interrupted?
>>
>> I've read the kasan/vmalloc.c comments and from them I'd extrapolate that the
>> caller needs to make sure there are not data races / memory barriers are in
>> place.
>
>KASAN does nothing to deliberately prevent or detect races. Even if
>the race leads to an OOB or UAF, KASAN might not be able to detect it.
>But sometimes it does: if poisoned shadow memory values become visible
>to the other thread/CPU before it makes a shadow memory value check.

Thanks :)

I've came up with a theoretical issue for the following dense series that might
happen if there is some racing but I'll have to experiment if it actually
happens.

-- 
Kind regards
Maciej Wieczór-Retman