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Fri, 13 Nov 2020 14:22:42 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from silver.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id NH9SLGGKr9ec for ; Fri, 13 Nov 2020 14:22:41 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by silver.osuosl.org (Postfix) with ESMTP id 3A1F9204AC for ; Fri, 13 Nov 2020 14:22:41 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 4940C142F; Fri, 13 Nov 2020 06:22:40 -0800 (PST) Received: from [10.57.53.43] (unknown [10.57.53.43]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 91AA73F6CF; Fri, 13 Nov 2020 06:22:38 -0800 (PST) Subject: Re: [RESEND][PATCH 2/2] iommu: Avoid crash if iommu_group is null To: John Stultz , lkml References: <20201112220520.48159-1-john.stultz@linaro.org> <20201112220520.48159-2-john.stultz@linaro.org> From: Robin Murphy Message-ID: <71d9e4f1-8205-0dec-5723-e1ae83389481@arm.com> Date: Fri, 13 Nov 2020 14:22:37 +0000 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:78.0) Gecko/20100101 Thunderbird/78.4.3 MIME-Version: 1.0 In-Reply-To: <20201112220520.48159-2-john.stultz@linaro.org> Content-Language: en-GB Cc: Maulik Shah , Saravana Kannan , Marc Zyngier , Lina Iyer , iommu@lists.linux-foundation.org, Andy Gross , linux-arm-msm , Will Deacon X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On 2020-11-12 22:05, John Stultz wrote: > In trying to handle a possible driver probe ordering issue > brought up by Robin Murphy, I ran across a separate null pointer > crash in the iommu core in iommu_group_remove_device(): > [ 2.732803] dwc3-qcom a6f8800.usb: failed to get usb-ddr path: -517 > [ 2.739281] Unable to handle kernel NULL pointer dereference at virtual address 00000000000000c0 > ... > [ 2.775619] [00000000000000c0] user address but active_mm is swapper > [ 2.782039] Internal error: Oops: 96000005 [#1] PREEMPT SMP > [ 2.787670] Modules linked in: > [ 2.790769] CPU: 6 PID: 1 Comm: swapper/0 Tainted: G W 5.10.0-rc1-mainline-00025-g272a618fc36-dirty #3973 > [ 2.801719] Hardware name: Thundercomm Dragonboard 845c (DT) > [ 2.807431] pstate: 00c00005 (nzcv daif +PAN +UAO -TCO BTYPE=--) > [ 2.813508] pc : iommu_group_remove_device+0x30/0x1b0 > [ 2.818611] lr : iommu_release_device+0x4c/0x78 > [ 2.823189] sp : ffffffc01005b950 > ... > [ 2.907082] Call trace: > [ 2.909566] iommu_group_remove_device+0x30/0x1b0 > [ 2.914323] iommu_release_device+0x4c/0x78 > [ 2.918559] iommu_bus_notifier+0xe8/0x108 > [ 2.922708] blocking_notifier_call_chain+0x78/0xb8 > [ 2.927641] device_del+0x2ac/0x3d0 > [ 2.931177] platform_device_del.part.9+0x20/0x98 > [ 2.935933] platform_device_unregister+0x2c/0x40 > [ 2.940694] of_platform_device_destroy+0xd8/0xe0 > [ 2.945450] device_for_each_child_reverse+0x58/0xb0 > [ 2.950471] of_platform_depopulate+0x4c/0x78 > [ 2.954886] dwc3_qcom_probe+0x93c/0xcb8 > [ 2.958858] platform_drv_probe+0x58/0xa8 > [ 2.962917] really_probe+0xec/0x398 > [ 2.966531] driver_probe_device+0x5c/0xb8 > [ 2.970677] device_driver_attach+0x74/0x98 > [ 2.974911] __driver_attach+0x60/0xe8 > [ 2.978700] bus_for_each_dev+0x84/0xd8 > [ 2.982581] driver_attach+0x30/0x40 > [ 2.986194] bus_add_driver+0x160/0x208 > [ 2.990076] driver_register+0x64/0x110 > [ 2.993957] __platform_driver_register+0x58/0x68 > [ 2.998716] dwc3_qcom_driver_init+0x20/0x28 > [ 3.003041] do_one_initcall+0x6c/0x2d0 > [ 3.006925] kernel_init_freeable+0x214/0x268 > [ 3.011339] kernel_init+0x18/0x118 > [ 3.014876] ret_from_fork+0x10/0x18 > [ 3.018495] Code: d0006a21 f9417295 91130021 910162b6 (b940c2a2) > > In the case above, the arm-smmu driver fails to probe with > EPROBE_DEFER, and I'm guessing I'm guessing that causes > iommu_group_add_device() to fail and sets the > dev->iommu_group = NULL, then somehow we hit > iommu_group_remove_device() and trip over the null value? > I'm not really sure... > > Anyway, adding the null check seems to avoid the issue and the > system boots fine after the arm-smmu driver later reprobed. > > Feedback or better ideas for a solution would be appreciated! I think the real issue is that we shouldn't even be here. If the device was still waiting for an IOMMU when it got torn down, then dev->iommu would be non-NULL due to a fwspec being allocated, but it's possible that none of the other setup would have been done, so iommu_release_device() shouldn't be blindly trying to undo it. It happens that iommu_device_unlink() and arm_smmu_release_device() still have some left-over tolerance for invalid inputs, but even if we do make iommu_group_remove_device() similarly tolerant of invalid input, the subsequent module_put() could still be unbalanced if the fwspec and deferral came from of_iommu_configure() without iommu_probe_device() even being called. Therefore I think this needs to be fundamentally fixed by making iommu_release_device() better at handling partially-configured devices in the first place. Robin. > Cc: Robin Murphy > Cc: Will Deacon > Cc: Andy Gross > Cc: Maulik Shah > Cc: Bjorn Andersson > Cc: Saravana Kannan > Cc: Marc Zyngier > Cc: Lina Iyer > Cc: iommu@lists.linux-foundation.org > Cc: linux-arm-msm > Signed-off-by: John Stultz > --- > drivers/iommu/iommu.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c > index b53446bb8c6b4..28229f7ef7d5a 100644 > --- a/drivers/iommu/iommu.c > +++ b/drivers/iommu/iommu.c > @@ -877,6 +877,10 @@ void iommu_group_remove_device(struct device *dev) > struct iommu_group *group = dev->iommu_group; > struct group_device *tmp_device, *device = NULL; > > + /* Avoid crash if iommu_group value is null */ > + if (!group) > + return; > + > dev_info(dev, "Removing from iommu group %d\n", group->id); > > /* Pre-notify listeners that a device is being removed. */ > _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu