On Tue, 2023-10-10 at 14:03 +0200, Hao Sun wrote: > 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> Please see a nitpick below. Acked-by: Eduard Zingerman <eddyz87@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), This change is not really necessary, the test reports same error either way. > 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,
