From: Chris Cole chris@sageembedded.com
[ Upstream commit a1208f6a822ac29933e772ef1f637c5d67838da9 ]
This patch addresses possible memory corruption when v7_dma_inv_range(start_address, end_address) address parameters are not aligned to whole cache lines. This function issues "invalidate" cache management operations to all cache lines from start_address (inclusive) to end_address (exclusive). When start_address and/or end_address are not aligned, the start and/or end cache lines are first issued "clean & invalidate" operation. The assumption is this is done to ensure that any dirty data addresses outside the address range (but part of the first or last cache lines) are cleaned/flushed so that data is not lost, which could happen if just an invalidate is issued.
The problem is that these first/last partial cache lines are issued "clean & invalidate" and then "invalidate". This second "invalidate" is not required and worse can cause "lost" writes to addresses outside the address range but part of the cache line. If another component writes to its part of the cache line between the "clean & invalidate" and "invalidate" operations, the write can get lost. This fix is to remove the extra "invalidate" operation when unaligned addressed are used.
A kernel module is available that has a stress test to reproduce the issue and a unit test of the updated v7_dma_inv_range(). It can be downloaded from http://ftp.sageembedded.com/outgoing/linux/cache-test-20181107.tgz.
v7_dma_inv_range() is call by dmac_[un]map_area(addr, len, direction) when the direction is DMA_FROM_DEVICE. One can (I believe) successfully argue that DMA from a device to main memory should use buffers aligned to cache line size, because the "clean & invalidate" might overwrite data that the device just wrote using DMA. But if a driver does use unaligned buffers, at least this fix will prevent memory corruption outside the buffer.
Signed-off-by: Chris Cole chris@sageembedded.com Signed-off-by: Russell King rmk+kernel@armlinux.org.uk Signed-off-by: Sasha Levin sashal@kernel.org --- arch/arm/mm/cache-v7.S | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/arch/arm/mm/cache-v7.S b/arch/arm/mm/cache-v7.S index de78109d002d..50a70edbc863 100644 --- a/arch/arm/mm/cache-v7.S +++ b/arch/arm/mm/cache-v7.S @@ -359,14 +359,16 @@ v7_dma_inv_range: ALT_UP(W(nop)) #endif mcrne p15, 0, r0, c7, c14, 1 @ clean & invalidate D / U line + addne r0, r0, r2
tst r1, r3 bic r1, r1, r3 mcrne p15, 0, r1, c7, c14, 1 @ clean & invalidate D / U line -1: - mcr p15, 0, r0, c7, c6, 1 @ invalidate D / U line - add r0, r0, r2 cmp r0, r1 +1: + mcrlo p15, 0, r0, c7, c6, 1 @ invalidate D / U line + addlo r0, r0, r2 + cmplo r0, r1 blo 1b dsb st ret lr