Overview
About vulnerability
In the Linux kernel, the following vulnerability has been resolved:
dmaengine: dma-axi-dmac: use DMA pool to manange DMA descriptor
For architectures like Microblaze or arm64 (where this IP is used), DMA_DIRECT_REMAP is set which means that dma_alloc_coherent() might remap (and hence vmalloc()) some memory. This became visible in a design where dma_direct_use_pool() is not possible.
With the above, when calling dma_free_coherent(), vunmap() would be called from softirq context and thus leading to a BUG().
To fix it, use a dma pool that is allocated in .device_alloc_chan_resources() and allocate blocks from it. The key point is that now dma_pool_free() is used in axi_dmac_free_desc() to free the blocks and that just frees the blocks from the pool in the sense they can be used again. In other words, no actual call to dma_free_coherent() happens. That only happens when destroying the pool in axi_dmac_free_chan_resources() which does not happen in any interrupt context.
Details
- Affected product:
- Debian 10 ELS
- Affected packages:
- linux @ 4.19.0