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tracing/dma: Cap dma_map_sg tracepoint arrays to prevent buffer overflow

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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: syzbot+28cea38c382fd15e751a@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=28cea38c382fd15e751a
Tested-by: syzbot+28cea38c382fd15e751a@syzkaller.appspotmail.com
Signed-off-by: Deepanshu Kartikey <Kartikey406@gmail.com>
Reviwed-by: Sean Anderson <sean.anderson@linux.dev>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Link: https://lore.kernel.org/r/20260130155215.69737-1-kartikey406@gmail.com
This commit is contained in:
Deepanshu Kartikey 2026-01-30 21:22:15 +05:30 • committed by Marek Szyprowski
parent 56c430c7f0
commit daafcc0ef0
1 changed files with 19 additions and 6 deletions
Download patch file Download diff file Expand all files Collapse all files

25
include/trace/events/dma.h
View file

@ -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)),