Messages in this thread Patch in this message | | | From | Gerald Schaefer <> | Subject | [RFC PATCH 1/1] dma-debug: fix check_for_illegal_area() in debug_dma_map_sg() | Date | Mon, 5 Jul 2021 20:52:52 +0200 |
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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 a broken logic in debug_dma_map_sg(). check_for_illegal_area() should check 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() contains 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 kernel start address of an sg element, and add the DMA length for overlap check, which can result in the false-positive warning because the DMA length can be larger than the actual single sg element length in kernel address space.
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").
Fixes: 884d05970bfb ("dma-debug: use sg_dma_len accessor") Tested-by: Niklas Schnelle <schnelle@linux.ibm.com> Signed-off-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com> --- kernel/dma/debug.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c index 14de1271463f..d7d44b7fe7e2 100644 --- a/kernel/dma/debug.c +++ b/kernel/dma/debug.c @@ -1299,6 +1299,12 @@ void debug_dma_map_sg(struct device *dev, struct scatterlist *sg, if (unlikely(dma_debug_disabled())) return; + for_each_sg(sg, s, nents, i) { + 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) @@ -1316,10 +1322,6 @@ void debug_dma_map_sg(struct device *dev, struct scatterlist *sg, 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); -- 2.25.1
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