From: Gerald Schaefer gerald.schaefer@linux.ibm.com
[ Upstream commit 293d92cbbd2418ca2ba43fed07f1b92e884d1c77 ]
The following warning occurred sporadically on s390: DMA-API: nvme 0006:00:00.0: device driver maps memory from kernel text or rodata [addr=0000000048cc5e2f] [len=131072] WARNING: CPU: 4 PID: 825 at kernel/dma/debug.c:1083 check_for_illegal_area+0xa8/0x138
It is a false-positive warning, due to broken logic in debug_dma_map_sg(). check_for_illegal_area() checks for overlay of sg elements with kernel text or rodata. It is called with sg_dma_len(s) instead of s->length as parameter. After the call to ->map_sg(), sg_dma_len() will contain the length of possibly combined sg elements in the DMA address space, and not the individual sg element length, which would be s->length.
The check will then use the physical start address of an sg element, and add the DMA length for the overlap check, which could result in the false warning, because the DMA length can be larger than the actual single sg element length.
In addition, the call to check_for_illegal_area() happens in the iteration over mapped_ents, which will not include all individual sg elements if any of them were combined in ->map_sg().
Fix this by using s->length instead of sg_dma_len(s). Also put the call to check_for_illegal_area() in a separate loop, iterating over all the individual sg elements ("nents" instead of "mapped_ents").
While at it, as suggested by Robin Murphy, also move check_for_stack() inside the new loop, as it is similarly concerned with validating the individual sg elements.
Link: https://lore.kernel.org/lkml/20210705185252.4074653-1-gerald.schaefer@linux.... Fixes: 884d05970bfb ("dma-debug: use sg_dma_len accessor") Signed-off-by: Gerald Schaefer gerald.schaefer@linux.ibm.com Signed-off-by: Christoph Hellwig hch@lst.de Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/dma/debug.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c index 01e893cf9b9f..b28665f4d8c7 100644 --- a/kernel/dma/debug.c +++ b/kernel/dma/debug.c @@ -1354,6 +1354,12 @@ void debug_dma_map_sg(struct device *dev, struct scatterlist *sg, if (unlikely(dma_debug_disabled())) return;
+ for_each_sg(sg, s, nents, i) { + check_for_stack(dev, sg_page(s), s->offset); + if (!PageHighMem(sg_page(s))) + check_for_illegal_area(dev, sg_virt(s), s->length); + } + for_each_sg(sg, s, mapped_ents, i) { entry = dma_entry_alloc(); if (!entry) @@ -1369,12 +1375,6 @@ void debug_dma_map_sg(struct device *dev, struct scatterlist *sg, entry->sg_call_ents = nents; entry->sg_mapped_ents = mapped_ents;
- check_for_stack(dev, sg_page(s), s->offset); - - if (!PageHighMem(sg_page(s))) { - check_for_illegal_area(dev, sg_virt(s), sg_dma_len(s)); - } - check_sg_segment(dev, s);
add_dma_entry(entry);