Currently, we don't check if the branch-taken of a jump is reserved code of ld_imm64. Instead, such a issue is captured in check_ld_imm(). The verifier gives the following log in such case: func#0 @0 0: R1=ctx(off=0,imm=0) R10=fp0 0: (18) r4 = 0xffff888103436000 ; R4_w=map_ptr(off=0,ks=4,vs=128,imm=0) 2: (18) r1 = 0x1d ; R1_w=29 4: (55) if r4 != 0x0 goto pc+4 ; R4_w=map_ptr(off=0,ks=4,vs=128,imm=0) 5: (1c) w1 -= w1 ; R1_w=0 6: (18) r5 = 0x32 ; R5_w=50 8: (56) if w5 != 0xfffffff4 goto pc-2 mark_precise: frame0: last_idx 8 first_idx 0 subseq_idx -1 mark_precise: frame0: regs=r5 stack= before 6: (18) r5 = 0x32 7: R5_w=50 7: BUG_ld_00 invalid BPF_LD_IMM insn Here the verifier rejects the program because it thinks insn at 7 is an invalid BPF_LD_IMM, but such a error log is not accurate since the issue is jumping to reserved code not because the program contains invalid insn. Therefore, make the verifier check the jump target during check_cfg(). For the same program, the verifier reports the following log: func#0 @0 jump to reserved code from insn 8 to 7 Also adjust existing tests in ld_imm64.c, testing forward/back jump to reserved code. Signed-off-by: Hao Sun <sunhao.th@xxxxxxxxx> --- Changes in v2: - Adjust existing test cases - Link to v1: https://lore.kernel.org/bpf/20231009-jmp-into-reserved-fields-v1-1-d8006e2ac1f6@xxxxxxxxx/ --- kernel/bpf/verifier.c | 7 +++++++ tools/testing/selftests/bpf/verifier/ld_imm64.c | 8 +++----- 2 files changed, 10 insertions(+), 5 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index eed7350e15f4..725ac0b464cf 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -14980,6 +14980,7 @@ static int push_insn(int t, int w, int e, struct bpf_verifier_env *env, { int *insn_stack = env->cfg.insn_stack; int *insn_state = env->cfg.insn_state; + struct bpf_insn *insns = env->prog->insnsi; if (e == FALLTHROUGH && insn_state[t] >= (DISCOVERED | FALLTHROUGH)) return DONE_EXPLORING; @@ -14993,6 +14994,12 @@ static int push_insn(int t, int w, int e, struct bpf_verifier_env *env, return -EINVAL; } + if (e == BRANCH && insns[w].code == 0) { + verbose_linfo(env, t, "%d", t); + verbose(env, "jump to reserved code from insn %d to %d\n", t, w); + return -EINVAL; + } + if (e == BRANCH) { /* mark branch target for state pruning */ mark_prune_point(env, w); diff --git a/tools/testing/selftests/bpf/verifier/ld_imm64.c b/tools/testing/selftests/bpf/verifier/ld_imm64.c index f9297900cea6..c34aa78f1877 100644 --- a/tools/testing/selftests/bpf/verifier/ld_imm64.c +++ b/tools/testing/selftests/bpf/verifier/ld_imm64.c @@ -9,22 +9,20 @@ BPF_MOV64_IMM(BPF_REG_0, 2), BPF_EXIT_INSN(), }, - .errstr = "invalid BPF_LD_IMM insn", - .errstr_unpriv = "R1 pointer comparison", + .errstr = "jump to reserved code", .result = REJECT, }, { "test2 ld_imm64", .insns = { - BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 0, 1), BPF_LD_IMM64(BPF_REG_0, 0), + BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 0, -2), BPF_LD_IMM64(BPF_REG_0, 0), BPF_LD_IMM64(BPF_REG_0, 1), BPF_LD_IMM64(BPF_REG_0, 1), BPF_EXIT_INSN(), }, - .errstr = "invalid BPF_LD_IMM insn", - .errstr_unpriv = "R1 pointer comparison", + .errstr = "jump to reserved code", .result = REJECT, }, { --- base-commit: 3157b7ce14bbf468b0ca8613322a05c37b5ae25d change-id: 20231009-jmp-into-reserved-fields-fc1a98a8e7dc Best regards, -- Hao Sun <sunhao.th@xxxxxxxxx>
