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 a fixed size of 128 entries. This limits the total event size to approximately 2,760 bytes, safely under the 8KB limit while still providing sufficient debugging information for typical cases. The tracepoint now records the full nents/ents counts and a truncated flag so users can see when data has been capped. Reported-by: [email protected] Closes: https://syzkaller.appspot.com/bug?extid=28cea38c382fd15e751a 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..c4e1a9f0c9c4 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, DMA_TRACE_MAX_ENTRIES) + __dynamic_array(u64, dma_addrs, DMA_TRACE_MAX_ENTRIES) + __dynamic_array(unsigned int, lengths, 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
