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Date:   Thu, 17 Sep 2020 12:05:17 -0400
From:   Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To:     Thomas Tai <thomas.tai@oracle.com>
Cc:     m.szyprowski@samsung.com, hch@lst.de, robin.murphy@arm.com,
        iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH V2] dma-direct: Fix potential NULL pointer dereference
Message-ID: <20200917160517.GB10122@char.us.oracle.com>
References: <1600289466-23805-1-git-send-email-thomas.tai@oracle.com>
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On Wed, Sep 16, 2020 at 02:51:06PM -0600, Thomas Tai wrote:
> When booting the kernel v5.9-rc4 on a VM, the kernel would panic when
> printing a warning message in swiotlb_map(). The dev->dma_mask must not
> be a NULL pointer when calling the dma mapping layer. A NULL pointer check
> can potentially avoid the panic.
> 
> [drm] Initialized virtio_gpu 0.1.0 0 for virtio0 on minor 0
>  BUG: kernel NULL pointer dereference, address: 0000000000000000
>  #PF: supervisor read access in kernel mode
>  #PF: error_code(0x0000) - not-present page
>  PGD 0 P4D 0
>  Oops: 0000 [#1] SMP PTI
>  CPU: 1 PID: 331 Comm: systemd-udevd Not tainted 5.9.0-rc4 #1
>  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009),
>  BIOS 1.13.0-1ubuntu1 04/01/2014
>  RIP: 0010:swiotlb_map+0x1ac/0x200
>  Code: e8 d9 fc ff ff 80 3d 92 ee 4c 01 00 75 51 49 8b 84 24 48 02 00 00
>  4d 8b 6c 24 50 c6 05 7c ee 4c 01 01 4d 8b bc 24 58 02 00 00 <4c> 8b 30
>  4d 85 ed 75 04 4d 8b 2c 24 4c 89 e7 e8 10 6b 4f 00 4d 89
>  RSP: 0018:ffff9f96801af6f8 EFLAGS: 00010246
>  RAX: 0000000000000000 RBX: 0000000000001000 RCX: 0000000000000080
>  RDX: 000000000000007f RSI: 0000000000000202 RDI: 0000000000000202
>  RBP: ffff9f96801af748 R08: ffffffffffffffff R09: 0000000000000020
>  R10: 0000000000000000 R11: ffff8fabfffa3000 R12: ffff8faad02c7810
>  R13: 0000000000000000 R14: 0000000000000020 R15: 0000000000000000
>  FS:  00007fabc63588c0(0000) GS:ffff8fabf7c80000(0000)
>  knlGS:0000000000000000
>  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>  CR2: 0000000000000000 CR3: 0000000151496005 CR4: 0000000000370ee0
>  DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>  DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>  Call Trace:
>   dma_direct_map_sg+0x124/0x210
>   dma_map_sg_attrs+0x32/0x50
>   drm_gem_shmem_get_pages_sgt+0x6a/0x90 [drm]
>   virtio_gpu_object_create+0x140/0x2f0 [virtio_gpu]
>   ? ww_mutex_unlock+0x26/0x30
>   virtio_gpu_mode_dumb_create+0xab/0x160 [virtio_gpu]
>   drm_mode_create_dumb+0x82/0x90 [drm]
>   drm_client_framebuffer_create+0xaa/0x200 [drm]
>   drm_fb_helper_generic_probe+0x59/0x150 [drm_kms_helper]
>   drm_fb_helper_single_fb_probe+0x29e/0x3e0 [drm_kms_helper]
>   __drm_fb_helper_initial_config_and_unlock+0x41/0xd0 [drm_kms_helper]
>   drm_fbdev_client_hotplug+0xe6/0x1a0 [drm_kms_helper]
>   drm_fbdev_generic_setup+0xaf/0x170 [drm_kms_helper]
>   virtio_gpu_probe+0xea/0x100 [virtio_gpu]
>   virtio_dev_probe+0x14b/0x1e0 [virtio]
>   really_probe+0x1db/0x440
>   driver_probe_device+0xe9/0x160
>   device_driver_attach+0x5d/0x70
>   __driver_attach+0x8f/0x150
>   ? device_driver_attach+0x70/0x70
>   bus_for_each_dev+0x7e/0xc0
>   driver_attach+0x1e/0x20
>   bus_add_driver+0x152/0x1f0
>   driver_register+0x74/0xd0
>   ? 0xffffffffc0529000
>   register_virtio_driver+0x20/0x30 [virtio]
>   virtio_gpu_driver_init+0x15/0x1000 [virtio_gpu]
>   do_one_initcall+0x4a/0x1fa
>   ? _cond_resched+0x19/0x30
>   ? kmem_cache_alloc_trace+0x16b/0x2e0
>   do_init_module+0x62/0x240
>   load_module+0xe0e/0x1100
>   ? security_kernel_post_read_file+0x5c/0x70
>   __do_sys_finit_module+0xbe/0x120
>   ? __do_sys_finit_module+0xbe/0x120
>   __x64_sys_finit_module+0x1a/0x20
>   do_syscall_64+0x38/0x50
>   entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> Signed-off-by: Thomas Tai <thomas.tai@oracle.com>

Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

Thank you!
> ---
>  include/linux/dma-direct.h |  3 ---
>  kernel/dma/mapping.c       | 11 +++++++++++
>  2 files changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/dma-direct.h b/include/linux/dma-direct.h
> index 6e87225..0648708 100644
> --- a/include/linux/dma-direct.h
> +++ b/include/linux/dma-direct.h
> @@ -62,9 +62,6 @@ static inline bool dma_capable(struct device *dev, dma_addr_t addr, size_t size,
>  {
>  	dma_addr_t end = addr + size - 1;
>  
> -	if (!dev->dma_mask)
> -		return false;
> -
>  	if (is_ram && !IS_ENABLED(CONFIG_ARCH_DMA_ADDR_T_64BIT) &&
>  	    min(addr, end) < phys_to_dma(dev, PFN_PHYS(min_low_pfn)))
>  		return false;
> diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
> index 0d12942..7133d5c 100644
> --- a/kernel/dma/mapping.c
> +++ b/kernel/dma/mapping.c
> @@ -144,6 +144,10 @@ dma_addr_t dma_map_page_attrs(struct device *dev, struct page *page,
>  	dma_addr_t addr;
>  
>  	BUG_ON(!valid_dma_direction(dir));
> +
> +	if (WARN_ON_ONCE(!dev->dma_mask))
> +		return DMA_MAPPING_ERROR;
> +
>  	if (dma_map_direct(dev, ops))
>  		addr = dma_direct_map_page(dev, page, offset, size, dir, attrs);
>  	else
> @@ -179,6 +183,10 @@ int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, int nents,
>  	int ents;
>  
>  	BUG_ON(!valid_dma_direction(dir));
> +
> +	if (WARN_ON_ONCE(!dev->dma_mask))
> +		return 0;
> +
>  	if (dma_map_direct(dev, ops))
>  		ents = dma_direct_map_sg(dev, sg, nents, dir, attrs);
>  	else
> @@ -213,6 +221,9 @@ dma_addr_t dma_map_resource(struct device *dev, phys_addr_t phys_addr,
>  
>  	BUG_ON(!valid_dma_direction(dir));
>  
> +	if (WARN_ON_ONCE(!dev->dma_mask))
> +		return DMA_MAPPING_ERROR;
> +
>  	/* Don't allow RAM to be mapped */
>  	if (WARN_ON_ONCE(pfn_valid(PHYS_PFN(phys_addr))))
>  		return DMA_MAPPING_ERROR;
> -- 
> 1.8.3.1
>