From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 07795C433EF for ; Fri, 8 Apr 2022 20:09:10 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 947116B007D; Fri, 8 Apr 2022 16:09:09 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 91DFB6B007E; Fri, 8 Apr 2022 16:09:09 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 7E6166B0080; Fri, 8 Apr 2022 16:09:09 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (relay.a.hostedemail.com [64.99.140.24]) by kanga.kvack.org (Postfix) with ESMTP id 708D76B007D for ; Fri, 8 Apr 2022 16:09:09 -0400 (EDT) Received: from smtpin11.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 461CD22DF4 for ; Fri, 8 Apr 2022 20:09:09 +0000 (UTC) X-FDA: 79334800818.11.E87AB9B Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by imf04.hostedemail.com (Postfix) with ESMTP id B1AD340003 for ; Fri, 8 Apr 2022 20:09:08 +0000 (UTC) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id D4EF8B82D64; Fri, 8 Apr 2022 20:09:06 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 943B7C385A5; Fri, 8 Apr 2022 20:09:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1649448545; bh=Uwe61k3TCdIIAb9jWMhOFX99NiRwkoxxsB+Q7xD3Mck=; h=Date:To:From:In-Reply-To:Subject:From; b=vP/PnsHIBa1QkY85u2AzCWADg8BR56BgOHgbNPxvhlodwAHV2uFg+4GZaQnYjzxR7 yTGwqWwXKwNBQeH/KgPabxhmHs3C/yGHkHOxAjQusbesROJyu/SMVuFs3OGvcXXsTI WxKEvc8QjUp4poAk0vPDkxfNm2Euhwq6YXdQ791g= Date: Fri, 08 Apr 2022 13:09:04 -0700 To: stable@vger.kernel.org,seanjc@google.com,pbonzini@redhat.com,akpm@linux-foundation.org,patches@lists.linux.dev,linux-mm@kvack.org,mm-commits@vger.kernel.org,torvalds@linux-foundation.org,akpm@linux-foundation.org From: Andrew Morton In-Reply-To: <20220408130819.a89195e527ce58dfbe0700b9@linux-foundation.org> Subject: [patch 5/9] mmmremap.c: avoid pointless invalidate_range_start/end on mremap(old_size=0) Message-Id: <20220408200905.943B7C385A5@smtp.kernel.org> X-Stat-Signature: xxo8epgcabfiuzs4pciu3oi4k4upypkd Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b="vP/PnsHI"; spf=pass (imf04.hostedemail.com: domain of akpm@linux-foundation.org designates 145.40.68.75 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org; dmarc=none X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: B1AD340003 X-HE-Tag: 1649448548-349809 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000014, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: From: Paolo Bonzini Subject: mmmremap.c: avoid pointless invalidate_range_start/end on mremap(old_size=0) If an mremap() syscall with old_size=0 ends up in move_page_tables(), it will call invalidate_range_start()/invalidate_range_end() unnecessarily, i.e. with an empty range. This causes a WARN in KVM's mmu_notifier. In the past, empty ranges have been diagnosed to be off-by-one bugs, hence the WARNing. Given the low (so far) number of unique reports, the benefits of detecting more buggy callers seem to outweigh the cost of having to fix cases such as this one, where userspace is doing something silly. In this particular case, an early return from move_page_tables() is enough to fix the issue. Link: https://lkml.kernel.org/r/20220329173155.172439-1-pbonzini@redhat.com Reported-by: syzbot+6bde52d89cfdf9f61425@syzkaller.appspotmail.com Signed-off-by: Paolo Bonzini Cc: Sean Christopherson Cc: Signed-off-by: Andrew Morton --- mm/mremap.c | 3 +++ 1 file changed, 3 insertions(+) --- a/mm/mremap.c~mm-avoid-pointless-invalidate_range_start-end-on-mremapold_size=0 +++ a/mm/mremap.c @@ -486,6 +486,9 @@ unsigned long move_page_tables(struct vm pmd_t *old_pmd, *new_pmd; pud_t *old_pud, *new_pud; + if (!len) + return 0; + old_end = old_addr + len; flush_cache_range(vma, old_addr, old_end); _