From: Maxim Mikityanskiy <maxim@xxxxxxxxxxxxx>
The goal of this series is to extend the verifier's capabilities of
tracking scalars when they are spilled to stack, especially when the
spill or fill is narrowing. It also contains a fix by Eduard for
infinite loop detection and a state pruning optimization by Eduard that
compensates for a verification complexity regression introduced by
tracking unbounded scalars. These improvements reduce the surface of
false rejections that I saw while working on Cilium codebase.
Patches 1-9 of the original series were previously applied in v2.
Patches 1-2 (Maxim): Support the case when boundary checks are first
performed after the register was spilled to the stack.
Patches 3-4 (Maxim): Support narrowing fills.
Patches 5-6 (Eduard): Optimization for state pruning in stacksafe() to
mitigate the verification complexity regression.
veristat -e file,prog,states -f '!states_diff<50' -f '!states_pct<10' -f '!states_a<10' -f '!states_b<10' -C ...
* Without patch 5:
File Program States (A) States (B) States (DIFF)
-------------------- -------- ---------- ---------- ----------------
pyperf100.bpf.o on_event 4878 6528 +1650 (+33.83%)
pyperf180.bpf.o on_event 6936 11032 +4096 (+59.05%)
pyperf600.bpf.o on_event 22271 39455 +17184 (+77.16%)
pyperf600_iter.bpf.o on_event 400 490 +90 (+22.50%)
strobemeta.bpf.o on_event 4895 14028 +9133 (+186.58%)
* With patch 5:
File Program States (A) States (B) States (DIFF)
----------------------- ------------- ---------- ---------- ---------------
bpf_xdp.o tail_lb_ipv4 2770 2224 -546 (-19.71%)
pyperf100.bpf.o on_event 4878 5848 +970 (+19.89%)
pyperf180.bpf.o on_event 6936 8868 +1932 (+27.85%)
pyperf600.bpf.o on_event 22271 29656 +7385 (+33.16%)
pyperf600_iter.bpf.o on_event 400 450 +50 (+12.50%)
xdp_synproxy_kern.bpf.o syncookie_tc 280 226 -54 (-19.29%)
xdp_synproxy_kern.bpf.o syncookie_xdp 302 228 -74 (-24.50%)
v2 changes:
Fixed comments in patch 1, moved endianness checks to header files in
patch 12 where possible, added Eduard's ACKs.
v3 changes:
Maxim: Removed __is_scalar_unbounded altogether, addressed Andrii's
comments.
Eduard: Patch #5 (#14 in v2) changed significantly:
- Logical changes:
- Handling of STACK_{MISC,ZERO} mix turned out to be incorrect:
a mix of MISC and ZERO in old state is not equivalent to e.g.
just MISC is current state, because verifier could have deduced
zero scalars from ZERO slots in old state for some loads.
- There is no reason to limit the change only to cases when
old or current stack is a spill of unbounded scalar,
it is valid to compare any 64-bit scalar spill with fake
register impersonating MISC.
- STACK_ZERO vs spilled zero case was dropped,
after recent changes for zero handling by Andrii and Yonghong
it is hard (impossible?) to conjure all ZERO slots for an spi.
=> the case does not make any difference in veristat results.
- Use global static variable for unbound_reg (Andrii)
- Code shuffling to remove duplication in stacksafe() (Andrii)
Eduard Zingerman (2):
bpf: handle scalar spill vs all MISC in stacksafe()
selftests/bpf: states pruning checks for scalar vs STACK_MISC
Maxim Mikityanskiy (4):
bpf: Track spilled unbounded scalars
selftests/bpf: Test tracking spilled unbounded scalars
bpf: Preserve boundaries and track scalars on narrowing fill
selftests/bpf: Add test cases for narrowing fill
include/linux/bpf_verifier.h | 9 +
kernel/bpf/verifier.c | 103 ++++--
.../selftests/bpf/progs/verifier_spill_fill.c | 324 +++++++++++++++++-
3 files changed, 404 insertions(+), 32 deletions(-)
--
2.43.0
