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Message-ID: <9913d026-fddd-c188-0873-0f7a66fb2c3c@arm.com>
Date: Tue, 18 Jan 2022 13:49:36 +0000
From: Robin Murphy <robin.murphy@....com>
To: Vijayanand Jitta <quic_vjitta@...cinc.com>, joro@...tes.org,
will@...nel.org, iommu@...ts.linux-foundation.org,
linux-kernel@...r.kernel.org
Cc: vjitta@...eaurora.org, kernel-team@...roid.com
Subject: Re: [PATCH v3] iommu: Fix potential use-after-free during probe
On 2022-01-12 13:13, Vijayanand Jitta wrote:
> Kasan has reported the following use after free on dev->iommu.
> when a device probe fails and it is in process of freeing dev->iommu
> in dev_iommu_free function, a deferred_probe_work_func runs in parallel
> and tries to access dev->iommu->fwspec in of_iommu_configure path thus
> causing use after free.
>
> BUG: KASAN: use-after-free in of_iommu_configure+0xb4/0x4a4
> Read of size 8 at addr ffffff87a2f1acb8 by task kworker/u16:2/153
>
> Workqueue: events_unbound deferred_probe_work_func
> Call trace:
> dump_backtrace+0x0/0x33c
> show_stack+0x18/0x24
> dump_stack_lvl+0x16c/0x1e0
> print_address_description+0x84/0x39c
> __kasan_report+0x184/0x308
> kasan_report+0x50/0x78
> __asan_load8+0xc0/0xc4
> of_iommu_configure+0xb4/0x4a4
> of_dma_configure_id+0x2fc/0x4d4
> platform_dma_configure+0x40/0x5c
> really_probe+0x1b4/0xb74
> driver_probe_device+0x11c/0x228
> __device_attach_driver+0x14c/0x304
> bus_for_each_drv+0x124/0x1b0
> __device_attach+0x25c/0x334
> device_initial_probe+0x24/0x34
> bus_probe_device+0x78/0x134
> deferred_probe_work_func+0x130/0x1a8
> process_one_work+0x4c8/0x970
> worker_thread+0x5c8/0xaec
> kthread+0x1f8/0x220
> ret_from_fork+0x10/0x18
>
> Allocated by task 1:
> ____kasan_kmalloc+0xd4/0x114
> __kasan_kmalloc+0x10/0x1c
> kmem_cache_alloc_trace+0xe4/0x3d4
> __iommu_probe_device+0x90/0x394
> probe_iommu_group+0x70/0x9c
> bus_for_each_dev+0x11c/0x19c
> bus_iommu_probe+0xb8/0x7d4
> bus_set_iommu+0xcc/0x13c
> arm_smmu_bus_init+0x44/0x130 [arm_smmu]
> arm_smmu_device_probe+0xb88/0xc54 [arm_smmu]
> platform_drv_probe+0xe4/0x13c
> really_probe+0x2c8/0xb74
> driver_probe_device+0x11c/0x228
> device_driver_attach+0xf0/0x16c
> __driver_attach+0x80/0x320
> bus_for_each_dev+0x11c/0x19c
> driver_attach+0x38/0x48
> bus_add_driver+0x1dc/0x3a4
> driver_register+0x18c/0x244
> __platform_driver_register+0x88/0x9c
> init_module+0x64/0xff4 [arm_smmu]
> do_one_initcall+0x17c/0x2f0
> do_init_module+0xe8/0x378
> load_module+0x3f80/0x4a40
> __se_sys_finit_module+0x1a0/0x1e4
> __arm64_sys_finit_module+0x44/0x58
> el0_svc_common+0x100/0x264
> do_el0_svc+0x38/0xa4
> el0_svc+0x20/0x30
> el0_sync_handler+0x68/0xac
> el0_sync+0x160/0x180
>
> Freed by task 1:
> kasan_set_track+0x4c/0x84
> kasan_set_free_info+0x28/0x4c
> ____kasan_slab_free+0x120/0x15c
> __kasan_slab_free+0x18/0x28
> slab_free_freelist_hook+0x204/0x2fc
> kfree+0xfc/0x3a4
> __iommu_probe_device+0x284/0x394
> probe_iommu_group+0x70/0x9c
> bus_for_each_dev+0x11c/0x19c
> bus_iommu_probe+0xb8/0x7d4
> bus_set_iommu+0xcc/0x13c
> arm_smmu_bus_init+0x44/0x130 [arm_smmu]
> arm_smmu_device_probe+0xb88/0xc54 [arm_smmu]
> platform_drv_probe+0xe4/0x13c
> really_probe+0x2c8/0xb74
> driver_probe_device+0x11c/0x228
> device_driver_attach+0xf0/0x16c
> __driver_attach+0x80/0x320
> bus_for_each_dev+0x11c/0x19c
> driver_attach+0x38/0x48
> bus_add_driver+0x1dc/0x3a4
> driver_register+0x18c/0x244
> __platform_driver_register+0x88/0x9c
> init_module+0x64/0xff4 [arm_smmu]
> do_one_initcall+0x17c/0x2f0
> do_init_module+0xe8/0x378
> load_module+0x3f80/0x4a40
> __se_sys_finit_module+0x1a0/0x1e4
> __arm64_sys_finit_module+0x44/0x58
> el0_svc_common+0x100/0x264
> do_el0_svc+0x38/0xa4
> el0_svc+0x20/0x30
> el0_sync_handler+0x68/0xac
> el0_sync+0x160/0x180
>
> Fix this by taking device_lock during probe_iommu_group.
>
> Signed-off-by: Vijayanand Jitta <quic_vjitta@...cinc.com>
> ---
> drivers/iommu/iommu.c | 12 ++++++++----
> 1 file changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index dd7863e..261792d 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -1617,7 +1617,7 @@ static int probe_iommu_group(struct device *dev, void *data)
> {
> struct list_head *group_list = data;
> struct iommu_group *group;
> - int ret;
> + int ret = 0;
>
> /* Device is probed already if in a group */
> group = iommu_group_get(dev);
> @@ -1626,9 +1626,13 @@ static int probe_iommu_group(struct device *dev, void *data)
> return 0;
> }
>
> - ret = __iommu_probe_device(dev, group_list);
> - if (ret == -ENODEV)
> - ret = 0;
> + ret = device_trylock(dev);
> + if (ret) {
This doesn't seem right - we can't have a non-deterministic situation
where __iommu_probe_device() may or may not be called depending on what
anyone else might be doing with the device at the same time.
I don't fully understand how __iommu_probe_device() and
of_iommu_configure() can be running for the same device at the same
time, but if that's not a race which can be fixed in its own right, then
I think adding a refcount to dev_iommu would be a more sensible way to
mitigate it.
Robin.
> + ret = __iommu_probe_device(dev, group_list);
> + if (ret == -ENODEV)
> + ret = 0;
> + device_unlock(dev);
> + }
>
> return ret;
> }
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