From d893dc26e3f42e12ae75703c52cc6de5578ff1f5 Mon Sep 17 00:00:00 2001 From: Edward Cree Date: Wed, 23 Aug 2017 15:09:46 +0100 Subject: [PATCH] selftests/bpf: add a test for a bug in liveness-based pruning Writes in straight-line code should not prevent reads from propagating along jumps. With current verifier code, the jump from 3 to 5 does not add a read mark on 3:R0 (because 5:R0 has a write mark), meaning that the jump from 1 to 3 gets pruned as safe even though R0 is NOT_INIT. Verifier output: 0: (61) r2 = *(u32 *)(r1 +0) 1: (35) if r2 >= 0x0 goto pc+1 R1=ctx(id=0,off=0,imm=0) R2=inv(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R10=fp0 2: (b7) r0 = 0 3: (35) if r2 >= 0x0 goto pc+1 R0=inv0 R1=ctx(id=0,off=0,imm=0) R2=inv(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R10=fp0 4: (b7) r0 = 0 5: (95) exit from 3 to 5: safe from 1 to 3: safe processed 8 insns, stack depth 0 Signed-off-by: Edward Cree Acked-by: Daniel Borkmann Acked-by: Alexei Starovoitov Signed-off-by: David S. Miller --- tools/testing/selftests/bpf/test_verifier.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c index c03542c417db..c912734d2364 100644 --- a/tools/testing/selftests/bpf/test_verifier.c +++ b/tools/testing/selftests/bpf/test_verifier.c @@ -6487,6 +6487,22 @@ static struct bpf_test tests[] = { .result = REJECT, .prog_type = BPF_PROG_TYPE_LWT_IN, }, + { + "liveness pruning and write screening", + .insns = { + /* Get an unknown value */ + BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1, 0), + /* branch conditions teach us nothing about R2 */ + BPF_JMP_IMM(BPF_JGE, BPF_REG_2, 0, 1), + BPF_MOV64_IMM(BPF_REG_0, 0), + BPF_JMP_IMM(BPF_JGE, BPF_REG_2, 0, 1), + BPF_MOV64_IMM(BPF_REG_0, 0), + BPF_EXIT_INSN(), + }, + .errstr = "R0 !read_ok", + .result = REJECT, + .prog_type = BPF_PROG_TYPE_LWT_IN, + }, }; static int probe_filter_length(const struct bpf_insn *fp) -- 2.20.1