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=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham 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 2791CC433FE for ; Wed, 9 Dec 2020 12:32:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EB91523C17 for ; Wed, 9 Dec 2020 12:32:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731716AbgLIMcX (ORCPT ); Wed, 9 Dec 2020 07:32:23 -0500 Received: from szxga05-in.huawei.com ([45.249.212.191]:9047 "EHLO szxga05-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730333AbgLIMcV (ORCPT ); Wed, 9 Dec 2020 07:32:21 -0500 Received: from DGGEMS412-HUB.china.huawei.com (unknown [172.30.72.60]) by szxga05-in.huawei.com (SkyGuard) with ESMTP id 4Crbxj5Jp1zhmwK; Wed, 9 Dec 2020 20:31:05 +0800 (CST) Received: from [127.0.0.1] (10.174.177.9) by DGGEMS412-HUB.china.huawei.com (10.3.19.212) with Microsoft SMTP Server id 14.3.487.0; Wed, 9 Dec 2020 20:31:27 +0800 Subject: Re: [RESEND PATCH v3 2/4] iommu/iova: Avoid double-negatives in magazine helpers To: John Garry , "robin.murphy@arm.com" , "joro@8bytes.org" , "will@kernel.org" CC: Linuxarm , "linux-kernel@vger.kernel.org" , "iommu@lists.linux-foundation.org" , "xiyou.wangcong@gmail.com" References: <1605608734-84416-1-git-send-email-john.garry@huawei.com> <1605608734-84416-3-git-send-email-john.garry@huawei.com> <7eb70f4b-b050-24ca-f1fa-d8f3c9ddce65@huawei.com> <7dfee7b0-0d51-b342-5318-09470c56f0d9@huawei.com> From: "Leizhen (ThunderTown)" Message-ID: Date: Wed, 9 Dec 2020 20:31:26 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <7dfee7b0-0d51-b342-5318-09470c56f0d9@huawei.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.177.9] X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020/12/9 19:39, John Garry wrote: > On 09/12/2020 09:03, Leizhen (ThunderTown) wrote: >> >> >> On 2020/11/17 18:25, John Garry wrote: >>> A similar crash to the following could be observed if initial CPU rcache >>> magazine allocations fail in init_iova_rcaches(): >>> >>> Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000 >>> Mem abort info: >>>     ESR = 0x96000004 >>>     EC = 0x25: DABT (current EL), IL = 32 bits >>>     SET = 0, FnV = 0 >>>     EA = 0, S1PTW = 0 >>> Data abort info: >>>     ISV = 0, ISS = 0x00000004 >>>     CM = 0, WnR = 0 >>> [0000000000000000] user address but active_mm is swapper >>> Internal error: Oops: 96000004 [#1] PREEMPT SMP >>> Modules linked in: >>> CPU: 11 PID: 696 Comm: irq/40-hisi_sas Not tainted 5.9.0-rc7-dirty #109 >>> Hardware name: Huawei D06 /D06, BIOS Hisilicon D06 UEFI RC0 - V1.16.01 03/15/2019 >>> Call trace: >>>    free_iova_fast+0xfc/0x280 >>>    iommu_dma_free_iova+0x64/0x70 >>>    __iommu_dma_unmap+0x9c/0xf8 >>>    iommu_dma_unmap_sg+0xa8/0xc8 >>>    dma_unmap_sg_attrs+0x28/0x50 >>>    cq_thread_v3_hw+0x2dc/0x528 >>>    irq_thread_fn+0x2c/0xa0 >>>    irq_thread+0x130/0x1e0 >>>    kthread+0x154/0x158 >>>    ret_from_fork+0x10/0x34 >>> >>> Code: f9400060 f102001f 54000981 d4210000 (f9400043) >>> >>>   ---[ end trace 4afcbdfc61b60467 ]--- >>> >>> The issue is that expression !iova_magazine_full(NULL) evaluates true; this >>> falls over in in __iova_rcache_insert() when we attempt to cache a mag >>> and cpu_rcache->loaded == NULL: >>> >>> if (!iova_magazine_full(cpu_rcache->loaded)) { >>>     can_insert = true; >>> ... >>> >>> if (can_insert) >>>     iova_magazine_push(cpu_rcache->loaded, iova_pfn); >>> >>> As above, can_insert is evaluated true, which it shouldn't be, and we try >>> to insert pfns in a NULL mag, which is not safe. >>> >>> To avoid this, stop using double-negatives, like !iova_magazine_full() and >>> !iova_magazine_empty(), and use positive tests, like >>> iova_magazine_has_space() and iova_magazine_has_pfns(), respectively; these >>> can safely deal with cpu_rcache->{loaded, prev} = NULL. >>> >>> Signed-off-by: John Garry > > Thanks for checking here... > >>> --- >>>   drivers/iommu/iova.c | 29 +++++++++++++++++------------ >>>   1 file changed, 17 insertions(+), 12 deletions(-) >>> >>> diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c >>> index 81b7399dd5e8..1f3f0f8b12e0 100644 >>> --- a/drivers/iommu/iova.c >>> +++ b/drivers/iommu/iova.c >>> @@ -827,14 +827,18 @@ iova_magazine_free_pfns(struct iova_magazine *mag, struct iova_domain *iovad) >>>       mag->size = 0; >>>   } >>>   -static bool iova_magazine_full(struct iova_magazine *mag) >>> +static bool iova_magazine_has_space(struct iova_magazine *mag) >>>   { >>> -    return (mag && mag->size == IOVA_MAG_SIZE); >>> +    if (!mag) >>> +        return false; >>> +    return mag->size < IOVA_MAG_SIZE; >>>   } >>>   -static bool iova_magazine_empty(struct iova_magazine *mag) >>> +static bool iova_magazine_has_pfns(struct iova_magazine *mag) >>>   { >>> -    return (!mag || mag->size == 0); >>> +    if (!mag) >>> +        return false; >>> +    return mag->size; >>>   } >>>     static unsigned long iova_magazine_pop(struct iova_magazine *mag, >>> @@ -843,7 +847,7 @@ static unsigned long iova_magazine_pop(struct iova_magazine *mag, >>>       int i; >>>       unsigned long pfn; >>>   -    BUG_ON(iova_magazine_empty(mag)); >>> +    BUG_ON(!iova_magazine_has_pfns(mag)); >>>         /* Only fall back to the rbtree if we have no suitable pfns at all */ >>>       for (i = mag->size - 1; mag->pfns[i] > limit_pfn; i--) >>> @@ -859,7 +863,7 @@ static unsigned long iova_magazine_pop(struct iova_magazine *mag, >>>     static void iova_magazine_push(struct iova_magazine *mag, unsigned long pfn) >>>   { >>> -    BUG_ON(iova_magazine_full(mag)); >>> +    BUG_ON(!iova_magazine_has_space(mag)); >>>         mag->pfns[mag->size++] = pfn; >>>   } >>> @@ -905,9 +909,9 @@ static bool __iova_rcache_insert(struct iova_domain *iovad, >>>       cpu_rcache = raw_cpu_ptr(rcache->cpu_rcaches); >>>       spin_lock_irqsave(&cpu_rcache->lock, flags); >>>   -    if (!iova_magazine_full(cpu_rcache->loaded)) { > > * > >>> +    if (iova_magazine_has_space(cpu_rcache->loaded)) { >>>           can_insert = true; >>> -    } else if (!iova_magazine_full(cpu_rcache->prev)) { >>> +    } else if (iova_magazine_has_space(cpu_rcache->prev)) { >>>           swap(cpu_rcache->prev, cpu_rcache->loaded); >>>           can_insert = true; >>>       } else { >>> @@ -916,8 +920,9 @@ static bool __iova_rcache_insert(struct iova_domain *iovad, >>>           if (new_mag) { >>>               spin_lock(&rcache->lock); >>>               if (rcache->depot_size < MAX_GLOBAL_MAGS) { >>> -                rcache->depot[rcache->depot_size++] = >>> -                        cpu_rcache->loaded; >>> +                if (cpu_rcache->loaded) >> >> Looks like it just needs to change this place. Compiler ensures that mag->size >> will not be accessed when mag is NULL. > > Not sure about that. We would get a crash prior to touching this codepath: > > So if cpu_rcache->loaded == NULL at entry, then !iova_magazine_full(cpu_rcache->loaded (==NULL) ) evaluates true, * above, so can_insert is set true, and we then attempt iova_magazine_push(cpu_rcache->loaded (==NULL), iova_pfn), which is not safe. > > ok? OK, I got it. Reviewed-by: Zhen Lei > > Cheers, > John > >> >> static bool iova_magazine_full(struct iova_magazine *mag) >> { >>          return (mag && mag->size == IOVA_MAG_SIZE); >> } >> >> static bool iova_magazine_empty(struct iova_magazine *mag) >> { >>          return (!mag || mag->size == 0); >> } >> > > > > >> >>> +                    rcache->depot[rcache->depot_size++] = >>> +                            cpu_rcache->loaded; >>>               } else { >>>                   mag_to_free = cpu_rcache->loaded; >>>               } >>> @@ -968,9 +973,9 @@ static unsigned long __iova_rcache_get(struct iova_rcache *rcache, >>>       cpu_rcache = raw_cpu_ptr(rcache->cpu_rcaches); >>>       spin_lock_irqsave(&cpu_rcache->lock, flags); >>>   -    if (!iova_magazine_empty(cpu_rcache->loaded)) { >>> +    if (iova_magazine_has_pfns(cpu_rcache->loaded)) { >>>           has_pfn = true; >>> -    } else if (!iova_magazine_empty(cpu_rcache->prev)) { >>> +    } else if (iova_magazine_has_pfns(cpu_rcache->prev)) { >>>           swap(cpu_rcache->prev, cpu_rcache->loaded); >>>           has_pfn = true; >>>       } else { >>> >> > > > . >