mbox series

[v9,00/14] Restricted DMA

Message ID 20210611152659.2142983-1-tientzu@chromium.org
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Series Restricted DMA | expand

Message

Claire Chang June 11, 2021, 3:26 p.m. UTC 
This series implements mitigations for lack of DMA access control on
systems without an IOMMU, which could result in the DMA accessing the
system memory at unexpected times and/or unexpected addresses, possibly
leading to data leakage or corruption.

For example, we plan to use the PCI-e bus for Wi-Fi and that PCI-e bus is
not behind an IOMMU. As PCI-e, by design, gives the device full access to
system memory, a vulnerability in the Wi-Fi firmware could easily escalate
to a full system exploit (remote wifi exploits: [1a], [1b] that shows a
full chain of exploits; [2], [3]).

To mitigate the security concerns, we introduce restricted DMA. Restricted
DMA utilizes the existing swiotlb to bounce streaming DMA in and out of a
specially allocated region and does memory allocation from the same region.
The feature on its own provides a basic level of protection against the DMA
overwriting buffer contents at unexpected times. However, to protect
against general data leakage and system memory corruption, the system needs
to provide a way to restrict the DMA to a predefined memory region (this is
usually done at firmware level, e.g. MPU in ATF on some ARM platforms [4]).

[1a] https://googleprojectzero.blogspot.com/2017/04/over-air-exploiting-broadcoms-wi-fi_4.html
[1b] https://googleprojectzero.blogspot.com/2017/04/over-air-exploiting-broadcoms-wi-fi_11.html
[2] https://blade.tencent.com/en/advisories/qualpwn/
[3] https://www.bleepingcomputer.com/news/security/vulnerabilities-found-in-highly-popular-firmware-for-wifi-chips/
[4] https://github.com/ARM-software/arm-trusted-firmware/blob/master/plat/mediatek/mt8183/drivers/emi_mpu/emi_mpu.c#L132

v9:
Address the comments in v7 to
  - set swiotlb active pool to dev->dma_io_tlb_mem
  - get rid of get_io_tlb_mem
  - dig out the device struct for is_swiotlb_active
  - move debugfs_create_dir out of swiotlb_create_debugfs
  - do set_memory_decrypted conditionally in swiotlb_init_io_tlb_mem
  - use IS_ENABLED in kernel/dma/direct.c
  - fix redefinition of 'of_dma_set_restricted_buffer'

v8:
- Fix reserved-memory.txt and add the reg property in example.
- Fix sizeof for of_property_count_elems_of_size in
  drivers/of/address.c#of_dma_set_restricted_buffer.
- Apply Will's suggestion to try the OF node having DMA configuration in
  drivers/of/address.c#of_dma_set_restricted_buffer.
- Fix typo in the comment of drivers/of/address.c#of_dma_set_restricted_buffer.
- Add error message for PageHighMem in
  kernel/dma/swiotlb.c#rmem_swiotlb_device_init and move it to
  rmem_swiotlb_setup.
- Fix the message string in rmem_swiotlb_setup.
https://lore.kernel.org/patchwork/cover/1437112/

v7:
Fix debugfs, PageHighMem and comment style in rmem_swiotlb_device_init
https://lore.kernel.org/patchwork/cover/1431031/

v6:
Address the comments in v5
https://lore.kernel.org/patchwork/cover/1423201/

v5:
Rebase on latest linux-next
https://lore.kernel.org/patchwork/cover/1416899/

v4:
- Fix spinlock bad magic
- Use rmem->name for debugfs entry
- Address the comments in v3
https://lore.kernel.org/patchwork/cover/1378113/

v3:
Using only one reserved memory region for both streaming DMA and memory
allocation.
https://lore.kernel.org/patchwork/cover/1360992/

v2:
Building on top of swiotlb.
https://lore.kernel.org/patchwork/cover/1280705/

v1:
Using dma_map_ops.
https://lore.kernel.org/patchwork/cover/1271660/


Claire Chang (14):
  swiotlb: Refactor swiotlb init functions
  swiotlb: Refactor swiotlb_create_debugfs
  swiotlb: Set dev->dma_io_tlb_mem to the swiotlb pool used
  swiotlb: Add restricted DMA pool initialization
  swiotlb: Update is_swiotlb_buffer to add a struct device argument
  swiotlb: Update is_swiotlb_active to add a struct device argument
  swiotlb: Bounce data from/to restricted DMA pool if available
  swiotlb: Move alloc_size to find_slots
  swiotlb: Refactor swiotlb_tbl_unmap_single
  dma-direct: Add a new wrapper __dma_direct_free_pages()
  swiotlb: Add restricted DMA alloc/free support.
  dma-direct: Allocate memory from restricted DMA pool if available
  dt-bindings: of: Add restricted DMA pool
  of: Add plumbing for restricted DMA pool

 .../reserved-memory/reserved-memory.txt       |  36 ++-
 drivers/gpu/drm/i915/gem/i915_gem_internal.c  |   2 +-
 drivers/gpu/drm/nouveau/nouveau_ttm.c         |   2 +-
 drivers/iommu/dma-iommu.c                     |  12 +-
 drivers/of/address.c                          |  33 +++
 drivers/of/device.c                           |   6 +
 drivers/of/of_private.h                       |   6 +
 drivers/pci/xen-pcifront.c                    |   2 +-
 drivers/xen/swiotlb-xen.c                     |   2 +-
 include/linux/device.h                        |   4 +
 include/linux/swiotlb.h                       |  45 +++-
 kernel/dma/Kconfig                            |  14 +
 kernel/dma/direct.c                           |  62 +++--
 kernel/dma/direct.h                           |   9 +-
 kernel/dma/swiotlb.c                          | 242 +++++++++++++-----
 15 files changed, 376 insertions(+), 101 deletions(-)

Comments

Christoph Hellwig June 14, 2021, 6:16 a.m. UTC | #1 
On Fri, Jun 11, 2021 at 11:26:46PM +0800, Claire Chang wrote:
> +	spin_lock_init(&mem->lock);

> +	for (i = 0; i < mem->nslabs; i++) {

> +		mem->slots[i].list = IO_TLB_SEGSIZE - io_tlb_offset(i);

> +		mem->slots[i].orig_addr = INVALID_PHYS_ADDR;

> +		mem->slots[i].alloc_size = 0;

> +	}

> +

> +	if (memory_decrypted)

> +		set_memory_decrypted((unsigned long)vaddr, bytes >> PAGE_SHIFT);

> +	memset(vaddr, 0, bytes);


We don't really need to do this call before the memset.  Which means we
can just move it to the callers that care instead of having a bool
argument.

Otherwise looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>
Christoph Hellwig June 14, 2021, 6:17 a.m. UTC | #2 
On Fri, Jun 11, 2021 at 11:26:47PM +0800, Claire Chang wrote:
> Split the debugfs creation to make the code reusable for supporting

> different bounce buffer pools, e.g. restricted DMA pool.

> 

> Signed-off-by: Claire Chang <tientzu@chromium.org>

> ---

>  kernel/dma/swiotlb.c | 23 ++++++++++++++++-------

>  1 file changed, 16 insertions(+), 7 deletions(-)

> 

> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c

> index 1a1208c81e85..8a3e2b3b246d 100644

> --- a/kernel/dma/swiotlb.c

> +++ b/kernel/dma/swiotlb.c

> @@ -64,6 +64,9 @@

>  enum swiotlb_force swiotlb_force;

>  

>  struct io_tlb_mem *io_tlb_default_mem;

> +#ifdef CONFIG_DEBUG_FS

> +static struct dentry *debugfs_dir;

> +#endif


What about moving this declaration into the main CONFIG_DEBUG_FS block
near the functions using it?

Otherwise looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>
Christoph Hellwig June 14, 2021, 6:25 a.m. UTC | #3 
On Fri, Jun 11, 2021 at 11:26:53PM +0800, Claire Chang wrote:
> Move the maintenance of alloc_size to find_slots for better code

> reusability later.


Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>
Christoph Hellwig June 14, 2021, 6:28 a.m. UTC | #4 
I think merging this with the next two patches would be a little more
clear.
Christoph Hellwig June 14, 2021, 6:28 a.m. UTC | #5 
On Mon, Jun 14, 2021 at 08:28:01AM +0200, Christoph Hellwig wrote:
> I think merging this with the next two patches would be a little more

> clear.


Sorry, I mean the next patch and the previous one.
Claire Chang June 15, 2021, 4:06 a.m. UTC | #6 
On Mon, Jun 14, 2021 at 2:16 PM Christoph Hellwig <hch@lst.de> wrote:
>
> On Fri, Jun 11, 2021 at 11:26:46PM +0800, Claire Chang wrote:
> > +     spin_lock_init(&mem->lock);
> > +     for (i = 0; i < mem->nslabs; i++) {
> > +             mem->slots[i].list = IO_TLB_SEGSIZE - io_tlb_offset(i);
> > +             mem->slots[i].orig_addr = INVALID_PHYS_ADDR;
> > +             mem->slots[i].alloc_size = 0;
> > +     }
> > +
> > +     if (memory_decrypted)
> > +             set_memory_decrypted((unsigned long)vaddr, bytes >> PAGE_SHIFT);
> > +     memset(vaddr, 0, bytes);
>
> We don't really need to do this call before the memset.  Which means we
> can just move it to the callers that care instead of having a bool
> argument.
>
> Otherwise looks good:
>
> Reviewed-by: Christoph Hellwig <hch@lst.de>

Thanks for the review. Will wait more days for other reviews and send
v10 to address the comments in this and other patches.
Claire Chang June 15, 2021, 1:30 p.m. UTC | #7 
v10 here: https://lore.kernel.org/patchwork/cover/1446882/