Merge branch 'bpf-bounded-loops'

Alexei Starovoitov says:

====================
v2->v3: fixed issues in backtracking pointed out by Andrii.
The next step is to add a lot more tests for backtracking.

v1->v2: addressed Andrii's feedback.

this patch set introduces verifier support for bounded loops and
adds several other improvements.
Ideally they would be introduced one at a time,
but to support bounded loop the verifier needs to 'step back'
in the patch 1. That patch introduces tracking of spill/fill
of constants through the stack. Though it's a useful feature
it hurts cilium tests.
Patch 3 introduces another feature by extending is_branch_taken
logic to 'if rX op rY' conditions. This feature is also
necessary to support bounded loops.
Then patch 4 adds support for the loops while adding
key heuristics with jmp_processed.
Introduction of parentage chain of verifier states in patch 4
allows patch 9 to add backtracking of precise scalar registers
which finally resolves degradation from patch 1.

The end result is much faster verifier for existing programs
and new support for loops.
See patch 8 for many kinds of loops that are now validated.
Patch 9 is the most tricky one and could be rewritten with
a different algorithm in the future.
====================

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

1 files changed, 4 insertions, 7 deletions

diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
index cd0248c54e25..93e1d87a343a 100644
--- a/tools/testing/selftests/bpf/test_verifier.c
+++ b/tools/testing/selftests/bpf/test_verifier.c
@@ -237,10 +237,10 @@ static void bpf_fill_scale1(struct bpf_test *self)
 		insn[i++] = BPF_STX_MEM(BPF_DW, BPF_REG_1, BPF_REG_6,
 					-8 * (k % 64 + 1));
 	}
-	/* every jump adds 1 step to insn_processed, so to stay exactly
-	 * within 1m limit add MAX_TEST_INSNS - MAX_JMP_SEQ - 1 MOVs and 1 EXIT
+	/* is_state_visited() doesn't allocate state for pruning for every jump.
+	 * Hence multiply jmps by 4 to accommodate that heuristic
 	 */
-	while (i < MAX_TEST_INSNS - MAX_JMP_SEQ - 1)
+	while (i < MAX_TEST_INSNS - MAX_JMP_SEQ * 4)
 		insn[i++] = BPF_ALU64_IMM(BPF_MOV, BPF_REG_0, 42);
 	insn[i] = BPF_EXIT_INSN();
 	self->prog_len = i + 1;
@@ -269,10 +269,7 @@ static void bpf_fill_scale2(struct bpf_test *self)
 		insn[i++] = BPF_STX_MEM(BPF_DW, BPF_REG_1, BPF_REG_6,
 					-8 * (k % (64 - 4 * FUNC_NEST) + 1));
 	}
-	/* every jump adds 1 step to insn_processed, so to stay exactly
-	 * within 1m limit add MAX_TEST_INSNS - MAX_JMP_SEQ - 1 MOVs and 1 EXIT
-	 */
-	while (i < MAX_TEST_INSNS - MAX_JMP_SEQ - 1)
+	while (i < MAX_TEST_INSNS - MAX_JMP_SEQ * 4)
 		insn[i++] = BPF_ALU64_IMM(BPF_MOV, BPF_REG_0, 42);
 	insn[i] = BPF_EXIT_INSN();
 	self->prog_len = i + 1;