From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f70.google.com (mail-wm0-f70.google.com [74.125.82.70]) by kanga.kvack.org (Postfix) with ESMTP id 33AAF6B0005 for ; Tue, 2 Aug 2016 06:05:31 -0400 (EDT) Received: by mail-wm0-f70.google.com with SMTP id p129so99830075wmp.3 for ; Tue, 02 Aug 2016 03:05:31 -0700 (PDT) Received: from mail-lf0-x232.google.com (mail-lf0-x232.google.com. [2a00:1450:4010:c07::232]) by mx.google.com with ESMTPS id e14si735934lfg.417.2016.08.02.03.05.29 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 02 Aug 2016 03:05:29 -0700 (PDT) Received: by mail-lf0-x232.google.com with SMTP id f93so134595111lfi.2 for ; Tue, 02 Aug 2016 03:05:29 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <57A06F23.9080804@virtuozzo.com> References: <1470063563-96266-1-git-send-email-glider@google.com> <57A06F23.9080804@virtuozzo.com> From: Alexander Potapenko Date: Tue, 2 Aug 2016 12:05:28 +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: Andrey Ryabinin Cc: Dmitriy Vyukov , Kostya Serebryany , Andrey Konovalov , Christoph Lameter , Andrew Morton , Steven Rostedt , Joonsoo Kim , Joonsoo Kim , Kuthonuzo Luruo , kasan-dev , LKML , Linux Memory Management List 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. AF= IAK this quite unusual. We were just reading the quarantine code, and Dmitry spotted the problem. I agree this is quite unusual, but we'd better prevent this case. >> 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, st= ruct 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 quarant= ine.\n", >> + ); > > Why WARN? I'd suggest pr_warn_once(); Agreed. I'll send the updated patch. (Sorry, Andrew, I'll have to get back to the non-tidy version then, as pr_warn_once() doesn't return the predicate value) >> + 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