From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-f69.google.com (mail-lf0-f69.google.com [209.85.215.69]) by kanga.kvack.org (Postfix) with ESMTP id 429776B0005 for ; Tue, 2 Aug 2016 06:07:11 -0400 (EDT) Received: by mail-lf0-f69.google.com with SMTP id e7so91122405lfe.0 for ; Tue, 02 Aug 2016 03:07:11 -0700 (PDT) Received: from mail-lf0-x231.google.com (mail-lf0-x231.google.com. [2a00:1450:4010:c07::231]) by mx.google.com with ESMTPS id 8si749300lfe.212.2016.08.02.03.07.09 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 02 Aug 2016 03:07:10 -0700 (PDT) Received: by mail-lf0-x231.google.com with SMTP id g62so134462595lfe.3 for ; Tue, 02 Aug 2016 03:07:09 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: References: <1470063563-96266-1-git-send-email-glider@google.com> <57A06F23.9080804@virtuozzo.com> From: Alexander Potapenko Date: Tue, 2 Aug 2016 12:07:08 +0200 Message-ID: Subject: Re: [PATCH] kasan: avoid overflowing quarantine size on low memory systems Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Dmitry Vyukov Cc: Andrey Ryabinin , Kostya Serebryany , Andrey Konovalov , Christoph Lameter , Andrew Morton , Steven Rostedt , Joonsoo Kim , Joonsoo Kim , Kuthonuzo Luruo , kasan-dev , LKML , "linux-mm@kvack.org" On Tue, Aug 2, 2016 at 12:05 PM, Dmitry Vyukov wrote: > On Tue, Aug 2, 2016 at 12:00 PM, Andrey Ryabinin > wrote: >> >> >> On 08/01/2016 05:59 PM, Alexander Potapenko wrote: >>> If the total amount of memory assigned to quarantine is less than the >>> amount of memory assigned to per-cpu quarantines, |new_quarantine_size| >>> may overflow. Instead, set it to zero. >>> >> >> Just curious, how did find this? >> Overflow is possible if system has more than 32 cpus per GB of memory. A= FIAK this quite unusual. > > I was reading code for unrelated reason. > >>> Reported-by: Dmitry Vyukov >>> Fixes: 55834c59098d ("mm: kasan: initial memory quarantine >>> implementation") >>> Signed-off-by: Alexander Potapenko >>> --- >>> mm/kasan/quarantine.c | 12 ++++++++++-- >>> 1 file changed, 10 insertions(+), 2 deletions(-) >>> >>> diff --git a/mm/kasan/quarantine.c b/mm/kasan/quarantine.c >>> index 65793f1..416d3b0 100644 >>> --- a/mm/kasan/quarantine.c >>> +++ b/mm/kasan/quarantine.c >>> @@ -196,7 +196,7 @@ void quarantine_put(struct kasan_free_meta *info, s= truct kmem_cache *cache) >>> >>> void quarantine_reduce(void) >>> { >>> - size_t new_quarantine_size; >>> + size_t new_quarantine_size, percpu_quarantines; >>> unsigned long flags; >>> struct qlist_head to_free =3D QLIST_INIT; >>> size_t size_to_free =3D 0; >>> @@ -214,7 +214,15 @@ void quarantine_reduce(void) >>> */ >>> new_quarantine_size =3D (READ_ONCE(totalram_pages) << PAGE_SHIFT)= / >>> QUARANTINE_FRACTION; >>> - new_quarantine_size -=3D QUARANTINE_PERCPU_SIZE * num_online_cpus= (); >>> + percpu_quarantines =3D QUARANTINE_PERCPU_SIZE * num_online_cpus()= ; >>> + if (new_quarantine_size < percpu_quarantines) { >>> + WARN_ONCE(1, >>> + "Too little memory, disabling global KASAN quaran= tine.\n", >>> + ); >> >> Why WARN? I'd suggest pr_warn_once(); > > > I would suggest to just do something useful. Setting quarantine > new_quarantine_size to 0 looks fine. > What would user do with this warning? Number of CPUs and amount of > memory are generally fixed. Why is it an issue for end user at all? We > still have some quarantine per-cpu. A WARNING means a [non-critical] > kernel bug. E.g. syzkaller will catch each and every boot of such > system as a bug. How about printk_once then? Silently setting the quarantine size to zero may puzzle the user. > >>> + new_quarantine_size =3D 0; >>> + } else { >>> + new_quarantine_size -=3D percpu_quarantines; >>> + } >>> WRITE_ONCE(quarantine_size, new_quarantine_size); >>> >>> last =3D global_quarantine.head; >>> --=20 Alexander Potapenko Software Engineer Google Germany GmbH Erika-Mann-Stra=C3=9Fe, 33 80636 M=C3=BCnchen Gesch=C3=A4ftsf=C3=BChrer: Matthew Scott Sucherman, Paul Terence Manicle Registergericht und -nummer: Hamburg, HRB 86891 Sitz der Gesellschaft: Hamburg -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org