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 X-Spam-Level: X-Spam-Status: No, score=-20.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B0975C4361B for ; Fri, 11 Dec 2020 22:36:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 851CF23C83 for ; Fri, 11 Dec 2020 22:36:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391914AbgLKVhc (ORCPT ); Fri, 11 Dec 2020 16:37:32 -0500 Received: from mail.kernel.org ([198.145.29.99]:60808 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2392319AbgLKVhS (ORCPT ); Fri, 11 Dec 2020 16:37:18 -0500 Date: Fri, 11 Dec 2020 13:36:31 -0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1607722592; bh=YTf/PmR8Znq9clmsPA1iOQkRargopVxOv9kb4NwAS7E=; h=From:To:Subject:In-Reply-To:From; b=nd21thy/eg+Xkx5Vn3N7D2EgIqY4NhFvzuQ3PkbdbrgFZxGe7s5lYgmpxk2+YyI2K EvgSHyncESQOORTbI0SPgFTp9VNwa7B3qWiRNTQ9dlEOWf6ehPpUwbMnyOYOA37Ezj 1iCxadW22T9d7hTtBxlkMAsXnrSdpcC00wBcDdkw= From: Andrew Morton To: adobriyan@gmail.com, akpm@linux-foundation.org, andreyknvl@google.com, aryabinin@virtuozzo.com, catalin.marinas@arm.com, dvyukov@google.com, ebiederm@xmission.com, elver@google.com, glider@google.com, linux-mm@kvack.org, miles.chen@mediatek.com, mm-commits@vger.kernel.org, song.bao.hua@hisilicon.com, stable@vger.kernel.org, torvalds@linux-foundation.org, vincenzo.frascino@arm.com, will@kernel.org Subject: [patch 2/8] proc: use untagged_addr() for pagemap_read addresses Message-ID: <20201211213631.mzQwOXkXF%akpm@linux-foundation.org> In-Reply-To: <20201211133555.88407977f082963499ed343c@linux-foundation.org> User-Agent: s-nail v14.8.16 Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org From: Miles Chen Subject: proc: use untagged_addr() for pagemap_read addresses When we try to visit the pagemap of a tagged userspace pointer, we find that the start_vaddr is not correct because of the tag. To fix it, we should untag the userspace pointers in pagemap_read(). I tested with 5.10-rc4 and the issue remains. Explanation from Catalin in [1]: :Arguably, that's a user-space bug since tagged file offsets were never :supported. In this case it's not even a tag at bit 56 as per the arm64 :tagged address ABI but rather down to bit 47. You could say that the :problem is caused by the C library (malloc()) or whoever created the :tagged vaddr and passed it to this function. It's not a kernel :regression as we've never supported it. : :Now, pagemap is a special case where the offset is usually not generated :as a classic file offset but rather derived by shifting a user virtual :address. I guess we can make a concession for pagemap (only) and allow :such offset with the tag at bit (56 - PAGE_SHIFT + 3). My test code is based on [2]: A userspace pointer which has been tagged by 0xb4: 0xb400007662f541c8 === userspace program === uint64 OsLayer::VirtualToPhysical(void *vaddr) { uint64 frame, paddr, pfnmask, pagemask; int pagesize = sysconf(_SC_PAGESIZE); off64_t off = ((uintptr_t)vaddr) / pagesize * 8; // off = 0xb400007662f541c8 / pagesize * 8 = 0x5a00003b317aa0 int fd = open(kPagemapPath, O_RDONLY); ... if (lseek64(fd, off, SEEK_SET) != off || read(fd, &frame, 8) != 8) { int err = errno; string errtxt = ErrorString(err); if (fd >= 0) close(fd); return 0; } ... } === kernel fs/proc/task_mmu.c === static ssize_t pagemap_read(struct file *file, char __user *buf, size_t count, loff_t *ppos) { ... src = *ppos; svpfn = src / PM_ENTRY_BYTES; // svpfn == 0xb400007662f54 start_vaddr = svpfn << PAGE_SHIFT; // start_vaddr == 0xb400007662f54000 end_vaddr = mm->task_size; /* watch out for wraparound */ // svpfn == 0xb400007662f54 // (mm->task_size >> PAGE) == 0x8000000 if (svpfn > mm->task_size >> PAGE_SHIFT) // the condition is true because of the tag 0xb4 start_vaddr = end_vaddr; ret = 0; while (count && (start_vaddr < end_vaddr)) { // we cannot visit correct entry because start_vaddr is set to end_vaddr int len; unsigned long end; ... } ... } [1] https://lore.kernel.org/patchwork/patch/1343258/ [2] https://github.com/stressapptest/stressapptest/blob/master/src/os.cc#L158 Link: https://lkml.kernel.org/r/20201204024347.8295-1-miles.chen@mediatek.com Signed-off-by: Miles Chen Reviewed-by: Vincenzo Frascino Reviewed-by: Catalin Marinas Cc: Alexey Dobriyan Cc: Andrey Konovalov Cc: Alexander Potapenko Cc: Vincenzo Frascino Cc: Andrey Ryabinin Cc: Catalin Marinas Cc: Dmitry Vyukov Cc: Marco Elver Cc: Will Deacon Cc: Eric W. Biederman Cc: Song Bao Hua (Barry Song) Cc: [5.4-] Signed-off-by: Andrew Morton --- fs/proc/task_mmu.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) --- a/fs/proc/task_mmu.c~proc-use-untagged_addr-for-pagemap_read-addresses +++ a/fs/proc/task_mmu.c @@ -1599,11 +1599,15 @@ static ssize_t pagemap_read(struct file src = *ppos; svpfn = src / PM_ENTRY_BYTES; - start_vaddr = svpfn << PAGE_SHIFT; end_vaddr = mm->task_size; /* watch out for wraparound */ - if (svpfn > mm->task_size >> PAGE_SHIFT) + start_vaddr = end_vaddr; + if (svpfn <= (ULONG_MAX >> PAGE_SHIFT)) + start_vaddr = untagged_addr(svpfn << PAGE_SHIFT); + + /* Ensure the address is inside the task */ + if (start_vaddr > mm->task_size) start_vaddr = end_vaddr; /* _