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• snd_sof_dsp_block_write(sdev, offset,
  

• 			(void *)block + sizeof(*block),
  

• 			block->size);
  

• /* next block */
  

• block = (void *)block + sizeof(*block) + block->size;
  

This may lead to an unaligned access.

Did you mean we should double check the block->size to prevent access to an invalid address?

You need two types of checks for the given data:

• The bounce check of block->size; We need to avoid out-of-bounce access.

s/bounce/bounds ?

• Alignment of block->size; For some non-x86 platforms, the access to an unaligned address might be illegal.

Maybe I am missing something but I don't see any sort of explicit restriction on alignment in the SOF tools. it looks implicit based on address offsets and bases.

Liam, do you see any negative side effects if we enforce a 32-bit alignment for all blocks (which essentially means all block sizes are multiple of 4)? we can try and experiment but it's better if we have an agreement on the design.

Oh, and recently another thing is sometimes needed for avoiding Spectre. This can be covered by array_index_nospec().

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Also how is the endianess guaranteed?

Did you mean we should guarantee the driver can work no matter what kernel's endianess is? ie. Use le32_to_cpu() to handle it?

Depends on the implementation. IIRC, topology API refuses the data in a different endianess by checking the magic number at beginning.

snd_sof_dsp_block_write() is implemented with a platform-specific callback, I'd expect any endianess issues to be handled in that platform-specific code?

On Fri, 21 Dec 2018 10:05:04 +0100, Bard liao wrote:

On 12/20/2018 11:07 PM, Pierre-Louis Bossart wrote:

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• snd_sof_dsp_block_write(sdev, offset,

+                    (void *)block + sizeof(*block), +                    block->size);

+        /* next block */ +        block = (void *)block + sizeof(*block) + block->size;

This may lead to an unaligned access.

Did you mean we should double check the block->size to prevent access to an invalid address?

You need two types of checks for the given data:

• The bounce check of block->size;

We need to avoid out-of-bounce access.

s/bounce/bounds ?

...

• Alignment of block->size;

For some non-x86 platforms, the access to an unaligned address might    be illegal.

Maybe I am missing something but I don't see any sort of explicit restriction on alignment in the SOF tools. it looks implicit based on address offsets and bases.

Maybe get_unaligned() is good enough to avoid unaligned access?

That's another option, but you'd need to put everywhere.

An alternative is to just copy the data on a new block header on the stack temporarily and refer it.

Or simply assuring the alignment by checking block->size as Pierre suggested...

Takashi

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Liam, do you see any negative side effects if we enforce a 32-bit alignment for all blocks (which essentially means all block sizes are multiple of 4)? we can try and experiment but it's better if we have an agreement on the design.