The dma_map_sg tracepoint can trigger a perf buffer overflow when tracing large scatter-gather lists. With devices like virtio-gpu creating large DRM buffers, nents can exceed 1000 entries, resulting in:
phys_addrs: 1000 * 8 bytes = 8,000 bytes dma_addrs: 1000 * 8 bytes = 8,000 bytes lengths: 1000 * 4 bytes = 4,000 bytes Total: ~20,000 bytes This exceeds PERF_MAX_TRACE_SIZE (8192 bytes), causing: WARNING: CPU: 0 PID: 5497 at kernel/trace/trace_event_perf.c:405 perf buffer not large enough, wanted 24620, have 8192 Cap all three dynamic arrays at 128 entries using min() in the array size calculation. This ensures arrays are only as large as needed (up to the cap), avoiding unnecessary memory allocation for small operations while preventing overflow for large ones. The tracepoint now records the full nents/ents counts and a truncated flag so users can see when data has been capped. Changes in v2: - Use min(nents, DMA_TRACE_MAX_ENTRIES) for dynamic array sizing instead of fixed DMA_TRACE_MAX_ENTRIES allocation (feedback from Steven Rostedt) - This allocates only what's needed up to the cap, avoiding waste for small operations Reported-by: [email protected] Closes: https://syzkaller.appspot.com/bug?extid=28cea38c382fd15e751a Tested-by: [email protected] Signed-off-by: Deepanshu Kartikey <[email protected]> --- include/trace/events/dma.h | 25 +++++++++++++++++++------ 1 file changed, 19 insertions(+), 6 deletions(-) diff --git a/include/trace/events/dma.h b/include/trace/events/dma.h index b3fef140ae15..33e99e792f1a 100644 --- a/include/trace/events/dma.h +++ b/include/trace/events/dma.h @@ -275,6 +275,8 @@ TRACE_EVENT(dma_free_sgt, sizeof(u64), sizeof(u64))) ); +#define DMA_TRACE_MAX_ENTRIES 128 + TRACE_EVENT(dma_map_sg, TP_PROTO(struct device *dev, struct scatterlist *sgl, int nents, int ents, enum dma_data_direction dir, unsigned long attrs), @@ -282,9 +284,12 @@ TRACE_EVENT(dma_map_sg, TP_STRUCT__entry( __string(device, dev_name(dev)) - __dynamic_array(u64, phys_addrs, nents) - __dynamic_array(u64, dma_addrs, ents) - __dynamic_array(unsigned int, lengths, ents) + __field(int, full_nents) + __field(int, full_ents) + __field(bool, truncated) + __dynamic_array(u64, phys_addrs, min(nents, DMA_TRACE_MAX_ENTRIES)) + __dynamic_array(u64, dma_addrs, min(ents, DMA_TRACE_MAX_ENTRIES)) + __dynamic_array(unsigned int, lengths, min(ents, DMA_TRACE_MAX_ENTRIES)) __field(enum dma_data_direction, dir) __field(unsigned long, attrs) ), @@ -292,11 +297,16 @@ TRACE_EVENT(dma_map_sg, TP_fast_assign( struct scatterlist *sg; int i; + int traced_nents = min_t(int, nents, DMA_TRACE_MAX_ENTRIES); + int traced_ents = min_t(int, ents, DMA_TRACE_MAX_ENTRIES); __assign_str(device); - for_each_sg(sgl, sg, nents, i) + __entry->full_nents = nents; + __entry->full_ents = ents; + __entry->truncated = (nents > DMA_TRACE_MAX_ENTRIES) || (ents > DMA_TRACE_MAX_ENTRIES); + for_each_sg(sgl, sg, traced_nents, i) ((u64 *)__get_dynamic_array(phys_addrs))[i] = sg_phys(sg); - for_each_sg(sgl, sg, ents, i) { + for_each_sg(sgl, sg, traced_ents, i) { ((u64 *)__get_dynamic_array(dma_addrs))[i] = sg_dma_address(sg); ((unsigned int *)__get_dynamic_array(lengths))[i] = @@ -306,9 +316,12 @@ TRACE_EVENT(dma_map_sg, __entry->attrs = attrs; ), - TP_printk("%s dir=%s dma_addrs=%s sizes=%s phys_addrs=%s attrs=%s", + TP_printk("%s dir=%s nents=%d/%d ents=%d/%d%s dma_addrs=%s sizes=%s phys_addrs=%s attrs=%s", __get_str(device), decode_dma_data_direction(__entry->dir), + min_t(int, __entry->full_nents, DMA_TRACE_MAX_ENTRIES), __entry->full_nents, + min_t(int, __entry->full_ents, DMA_TRACE_MAX_ENTRIES), __entry->full_ents, + __entry->truncated ? " [TRUNCATED]" : "", __print_array(__get_dynamic_array(dma_addrs), __get_dynamic_array_len(dma_addrs) / sizeof(u64), sizeof(u64)), -- 2.43.0
