Invalidating the buffer memory in arch_sync_dma_for_device() for FROM_DEVICE transfers

When using the streaming DMA API to map a buffer prior to inbound non-coherent DMA (i.e. DMA_FROM_DEVICE), we invalidate any dirty CPU cachelines so that they will not be written back during the transfer and corrupt the buffer contents written by the DMA. This, however, poses two potential problems:

(1) If the DMA transfer does not write to every byte in the buffer, then the unwritten bytes will contain stale data once the transfer has completed.

(2) If the buffer has a virtual alias in userspace, then stale data may be visible via this alias during the period between performing the cache invalidation and the DMA writes landing in memory.

Address both of these issues by cleaning (aka writing-back) the dirty lines in arch_sync_dma_for_device(DMA_FROM_DEVICE) instead of discarding them using invalidation.

Cc: Ard Biesheuvel ardb@kernel.org Cc: Christoph Hellwig hch@lst.de Cc: Catalin Marinas catalin.marinas@arm.com Cc: Robin Murphy robin.murphy@arm.com Cc: Russell King linux@armlinux.org.uk Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20220606152150.GA31568@willie-the-truck Signed-off-by: Will Deacon will@kernel.org --- arch/arm64/mm/cache.S | 2 -- 1 file changed, 2 deletions(-)

diff --git a/arch/arm64/mm/cache.S b/arch/arm64/mm/cache.S index 0ea6cc25dc66..21c907987080 100644 --- a/arch/arm64/mm/cache.S +++ b/arch/arm64/mm/cache.S @@ -218,8 +218,6 @@ SYM_FUNC_ALIAS(__dma_flush_area, __pi___dma_flush_area) */ SYM_FUNC_START(__pi___dma_map_area) add x1, x0, x1 - cmp w2, #DMA_FROM_DEVICE - b.eq __pi_dcache_inval_poc b __pi_dcache_clean_poc SYM_FUNC_END(__pi___dma_map_area) SYM_FUNC_ALIAS(__dma_map_area, __pi___dma_map_area)