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[134.134.136.65]) by mx.google.com with ESMTPS id w5si8086075plz.387.2019.04.23.09.04.45 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 23 Apr 2019 09:04:45 -0700 (PDT) Received-SPF: pass (google.com: domain of dave.hansen@intel.com designates 134.134.136.65 as permitted sender) client-ip=134.134.136.65; Authentication-Results: mx.google.com; spf=pass (google.com: domain of dave.hansen@intel.com designates 134.134.136.65 as permitted sender) smtp.mailfrom=dave.hansen@intel.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=intel.com X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga006.jf.intel.com ([10.7.209.51]) by orsmga103.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 23 Apr 2019 09:04:45 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.60,386,1549958400"; d="scan'208";a="138130319" Received: from ray.jf.intel.com (HELO [10.7.201.133]) ([10.7.201.133]) by orsmga006.jf.intel.com with ESMTP; 23 Apr 2019 09:04:45 -0700 Subject: Re: [PATCH] x86/mpx: fix recursive munmap() corruption To: Laurent Dufour , Michael Ellerman , Thomas Gleixner , Dave Hansen Cc: LKML , rguenther@suse.de, mhocko@suse.com, vbabka@suse.cz, luto@amacapital.net, x86@kernel.org, Andrew Morton , linux-mm@kvack.org, stable@vger.kernel.org References: <20190401141549.3F4721FE@viggo.jf.intel.com> <87d0lht1c0.fsf@concordia.ellerman.id.au> <6718ede2-1fcb-1a8f-a116-250eef6416c7@linux.vnet.ibm.com> From: Dave Hansen Openpgp: preference=signencrypt Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <6718ede2-1fcb-1a8f-a116-250eef6416c7@linux.vnet.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 4/23/19 4:16 AM, Laurent Dufour wrote: > My only concern is the error path. > Calling arch_unmap() before handling any error case means that it will > have to be undo and there is no way to do so. Is there a practical scenario where munmap() of the VDSO can split a VMA? If the VDSO is guaranteed to be a single page, it would have to be a scenario where munmap() was called on a range that included the VDSO *and* other VMA that we failed to split. But, the scenario would have to be that someone tried to munmap() the VDSO and something adjacent, the munmap() failed, and they kept on using the VDSO and expected the special signal and perf behavior to be maintained. BTW, what keeps the VDSO from merging with an adjacent VMA? Is it just the vm_ops->close that comes from special_mapping_vmops? > I don't know what is the rational to move arch_unmap() to the beginning > of __do_munmap() but the error paths must be managed. It's in the changelog: https://patchwork.kernel.org/patch/10909727/ But, the tl;dr version is: x86 is recursively calling __do_unmap() (via arch_unmap()) in a spot where the internal rbtree data is inconsistent, which causes all kinds of fun. If we move arch_unmap() to before __do_munmap() does any data structure manipulation, the recursive call doesn't get confused any more. > There are 2 assumptions here: > 1. 'start' and 'end' are page aligned (this is guaranteed by __do_munmap(). > 2. the VDSO is 1 page (this is guaranteed by the union vdso_data_store on powerpc) Are you sure about #2? The 'vdso64_pages' variable seems rather unnecessary if the VDSO is only 1 page. ;)