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6361cd26e4
A test case with ridiculously deep bpf_for() nesting and
a conditional update of a stack location.
Consider the innermost loop structure:
1: bpf_for(o, 0, 10)
2: if (unlikely(bpf_get_prandom_u32()))
3: buf[0] = 42;
4: <exit>
Assuming that verifier.c:clean_live_states() operates w/o change from
the previous patch (e.g. as on current master) verification would
proceed as follows:
- at (1) state {buf[0]=?,o=drained}:
- checkpoint
- push visit to (2) for later
- at (4) {buf[0]=?,o=drained}
- pop (2) {buf[0]=?,o=active}, push visit to (3) for later
- at (1) {buf[0]=?,o=active}
- checkpoint
- push visit to (2) for later
- at (4) {buf[0]=?,o=drained}
- pop (2) {buf[0]=?,o=active}, push visit to (3) for later
- at (1) {buf[0]=?,o=active}:
- checkpoint reached, checkpoint's branch count becomes 0
- checkpoint is processed by clean_live_states() and
becomes {o=active}
- pop (3) {buf[0]=42,o=active}
- at (1), {buf[0]=42,o=active}
- checkpoint
- push visit to (2) for later
- at (4) {buf[0]=42,o=drained}
- pop (2) {buf[0]=42,o=active}, push visit to (3) for later
- at (1) {buf[0]=42,o=active}, checkpoint reached
- pop (3) {buf[0]=42,o=active}
- at (1) {buf[0]=42,o=active}:
- checkpoint reached, checkpoint's branch count becomes 0
- checkpoint is processed by clean_live_states() and
becomes {o=active}
- ...
Note how clean_live_states() converted the checkpoint
{buf[0]=42,o=active} to {o=active} and it can no longer be matched
against {buf[0]=<any>,o=active}, because iterator based states
are compared using stacksafe(... RANGE_WITHIN), that requires
stack slots to have same types. At the same time there are
still states {buf[0]=42,o=active} pushed to DFS stack.
This behaviour becomes exacerbated with multiple nesting levels,
here are veristat results:
- nesting level 1: 69 insns
- nesting level 2: 258 insns
- nesting level 3: 900 insns
- nesting level 4: 4754 insns
- nesting level 5: 35944 insns
- nesting level 6: 312558 insns
- nesting level 7: 1M limit
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20250215110411.3236773-5-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
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| .. | ||
| accounting | ||
| arch | ||
| bootconfig | ||
| bpf | ||
| build | ||
| certs | ||
| cgroup | ||
| counter | ||
| crypto | ||
| debugging | ||
| firewire | ||
| firmware | ||
| gpio | ||
| hv | ||
| iio | ||
| include | ||
| kvm/kvm_stat | ||
| laptop | ||
| leds | ||
| lib | ||
| memory-model | ||
| mm | ||
| net | ||
| objtool | ||
| pcmcia | ||
| perf | ||
| power | ||
| rcu | ||
| sched_ext | ||
| scripts | ||
| sound | ||
| spi | ||
| testing | ||
| thermal | ||
| time | ||
| tracing | ||
| usb | ||
| verification | ||
| virtio | ||
| wmi | ||
| workqueue | ||
| writeback | ||
| Makefile | ||