From 6f16101e6a8b4324c36e58a29d9e0dbb287cdedb Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Thu, 18 Jan 2018 01:15:21 +0100 Subject: [PATCH] bpf: mark dst unknown on inconsistent {s, u}bounds adjustments syzkaller generated a BPF proglet and triggered a warning with the following: 0: (b7) r0 = 0 1: (d5) if r0 s<= 0x0 goto pc+0 R0=inv0 R1=ctx(id=0,off=0,imm=0) R10=fp0 2: (1f) r0 -= r1 R0=inv0 R1=ctx(id=0,off=0,imm=0) R10=fp0 verifier internal error: known but bad sbounds What happens is that in the first insn, r0's min/max value are both 0 due to the immediate assignment, later in the jsle test the bounds are updated for the min value in the false path, meaning, they yield smin_val = 1, smax_val = 0, and when ctx pointer is subtracted from r0, verifier bails out with the internal error and throwing a WARN since smin_val != smax_val for the known constant. For min_val > max_val scenario it means that reg_set_min_max() and reg_set_min_max_inv() (which both refine existing bounds) demonstrated that such branch cannot be taken at runtime. In above scenario for the case where it will be taken, the existing [0, 0] bounds are kept intact. Meaning, the rejection is not due to a verifier internal error, and therefore the WARN() is not necessary either. We could just reject such cases in adjust_{ptr,scalar}_min_max_vals() when either known scalars have smin_val != smax_val or umin_val != umax_val or any scalar reg with bounds smin_val > smax_val or umin_val > umax_val. However, there may be a small risk of breakage of buggy programs, so handle this more gracefully and in adjust_{ptr,scalar}_min_max_vals() just taint the dst reg as unknown scalar when we see ops with such kind of src reg. Reported-by: syzbot+6d362cadd45dc0a12ba4@syzkaller.appspotmail.com Signed-off-by: Daniel Borkmann Signed-off-by: Alexei Starovoitov --- kernel/bpf/verifier.c | 27 +++-- tools/testing/selftests/bpf/test_verifier.c | 123 +++++++++++++++++++- 2 files changed, 138 insertions(+), 12 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index eb062b0fbf27..13551e623501 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -1895,17 +1895,13 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, dst_reg = ®s[dst]; - if (WARN_ON_ONCE(known && (smin_val != smax_val))) { - print_verifier_state(env, env->cur_state); - verbose(env, - "verifier internal error: known but bad sbounds\n"); - return -EINVAL; - } - if (WARN_ON_ONCE(known && (umin_val != umax_val))) { - print_verifier_state(env, env->cur_state); - verbose(env, - "verifier internal error: known but bad ubounds\n"); - return -EINVAL; + if ((known && (smin_val != smax_val || umin_val != umax_val)) || + smin_val > smax_val || umin_val > umax_val) { + /* Taint dst register if offset had invalid bounds derived from + * e.g. dead branches. + */ + __mark_reg_unknown(dst_reg); + return 0; } if (BPF_CLASS(insn->code) != BPF_ALU64) { @@ -2097,6 +2093,15 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env, src_known = tnum_is_const(src_reg.var_off); dst_known = tnum_is_const(dst_reg->var_off); + if ((src_known && (smin_val != smax_val || umin_val != umax_val)) || + smin_val > smax_val || umin_val > umax_val) { + /* Taint dst register if offset had invalid bounds derived from + * e.g. dead branches. + */ + __mark_reg_unknown(dst_reg); + return 0; + } + if (!src_known && opcode != BPF_ADD && opcode != BPF_SUB && opcode != BPF_AND) { __mark_reg_unknown(dst_reg); diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c index 67e7c41674d2..5ed4175c4ff8 100644 --- a/tools/testing/selftests/bpf/test_verifier.c +++ b/tools/testing/selftests/bpf/test_verifier.c @@ -6732,7 +6732,7 @@ static struct bpf_test tests[] = { BPF_JMP_IMM(BPF_JA, 0, 0, -7), }, .fixup_map1 = { 4 }, - .errstr = "unbounded min value", + .errstr = "R0 invalid mem access 'inv'", .result = REJECT, }, { @@ -8633,6 +8633,127 @@ static struct bpf_test tests[] = { .prog_type = BPF_PROG_TYPE_XDP, .flags = F_NEEDS_EFFICIENT_UNALIGNED_ACCESS, }, + { + "check deducing bounds from const, 1", + .insns = { + BPF_MOV64_IMM(BPF_REG_0, 1), + BPF_JMP_IMM(BPF_JSGE, BPF_REG_0, 1, 0), + BPF_ALU64_REG(BPF_SUB, BPF_REG_0, BPF_REG_1), + BPF_EXIT_INSN(), + }, + .result = REJECT, + .errstr = "R0 tried to subtract pointer from scalar", + }, + { + "check deducing bounds from const, 2", + .insns = { + BPF_MOV64_IMM(BPF_REG_0, 1), + BPF_JMP_IMM(BPF_JSGE, BPF_REG_0, 1, 1), + BPF_EXIT_INSN(), + BPF_JMP_IMM(BPF_JSLE, BPF_REG_0, 1, 1), + BPF_EXIT_INSN(), + BPF_ALU64_REG(BPF_SUB, BPF_REG_1, BPF_REG_0), + BPF_EXIT_INSN(), + }, + .result = ACCEPT, + }, + { + "check deducing bounds from const, 3", + .insns = { + BPF_MOV64_IMM(BPF_REG_0, 0), + BPF_JMP_IMM(BPF_JSLE, BPF_REG_0, 0, 0), + BPF_ALU64_REG(BPF_SUB, BPF_REG_0, BPF_REG_1), + BPF_EXIT_INSN(), + }, + .result = REJECT, + .errstr = "R0 tried to subtract pointer from scalar", + }, + { + "check deducing bounds from const, 4", + .insns = { + BPF_MOV64_IMM(BPF_REG_0, 0), + BPF_JMP_IMM(BPF_JSLE, BPF_REG_0, 0, 1), + BPF_EXIT_INSN(), + BPF_JMP_IMM(BPF_JSGE, BPF_REG_0, 0, 1), + BPF_EXIT_INSN(), + BPF_ALU64_REG(BPF_SUB, BPF_REG_1, BPF_REG_0), + BPF_EXIT_INSN(), + }, + .result = ACCEPT, + }, + { + "check deducing bounds from const, 5", + .insns = { + BPF_MOV64_IMM(BPF_REG_0, 0), + BPF_JMP_IMM(BPF_JSGE, BPF_REG_0, 0, 1), + BPF_ALU64_REG(BPF_SUB, BPF_REG_0, BPF_REG_1), + BPF_EXIT_INSN(), + }, + .result = REJECT, + .errstr = "R0 tried to subtract pointer from scalar", + }, + { + "check deducing bounds from const, 6", + .insns = { + BPF_MOV64_IMM(BPF_REG_0, 0), + BPF_JMP_IMM(BPF_JSGE, BPF_REG_0, 0, 1), + BPF_EXIT_INSN(), + BPF_ALU64_REG(BPF_SUB, BPF_REG_0, BPF_REG_1), + BPF_EXIT_INSN(), + }, + .result = REJECT, + .errstr = "R0 tried to subtract pointer from scalar", + }, + { + "check deducing bounds from const, 7", + .insns = { + BPF_MOV64_IMM(BPF_REG_0, ~0), + BPF_JMP_IMM(BPF_JSGE, BPF_REG_0, 0, 0), + BPF_ALU64_REG(BPF_SUB, BPF_REG_1, BPF_REG_0), + BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1, + offsetof(struct __sk_buff, mark)), + BPF_EXIT_INSN(), + }, + .result = REJECT, + .errstr = "dereference of modified ctx ptr", + }, + { + "check deducing bounds from const, 8", + .insns = { + BPF_MOV64_IMM(BPF_REG_0, ~0), + BPF_JMP_IMM(BPF_JSGE, BPF_REG_0, 0, 1), + BPF_ALU64_REG(BPF_ADD, BPF_REG_1, BPF_REG_0), + BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1, + offsetof(struct __sk_buff, mark)), + BPF_EXIT_INSN(), + }, + .result = REJECT, + .errstr = "dereference of modified ctx ptr", + }, + { + "check deducing bounds from const, 9", + .insns = { + BPF_MOV64_IMM(BPF_REG_0, 0), + BPF_JMP_IMM(BPF_JSGE, BPF_REG_0, 0, 0), + BPF_ALU64_REG(BPF_SUB, BPF_REG_0, BPF_REG_1), + BPF_EXIT_INSN(), + }, + .result = REJECT, + .errstr = "R0 tried to subtract pointer from scalar", + }, + { + "check deducing bounds from const, 10", + .insns = { + BPF_MOV64_IMM(BPF_REG_0, 0), + BPF_JMP_IMM(BPF_JSLE, BPF_REG_0, 0, 0), + /* Marks reg as unknown. */ + BPF_ALU64_IMM(BPF_NEG, BPF_REG_0, 0), + BPF_ALU64_REG(BPF_SUB, BPF_REG_0, BPF_REG_1), + BPF_EXIT_INSN(), + }, + .result = REJECT, + .errstr = "math between ctx pointer and register with unbounded min value is not allowed", + }, { "bpf_exit with invalid return code. test1", .insns = {