From d3bd7413e0ca40b60cf60d4003246d067cafdeda Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Sun, 6 Jan 2019 00:54:37 +0100 Subject: [PATCH 1/2] bpf: fix sanitation of alu op with pointer / scalar type from different paths While 979d63d50c0c ("bpf: prevent out of bounds speculation on pointer arithmetic") took care of rejecting alu op on pointer when e.g. pointer came from two different map values with different map properties such as value size, Jann reported that a case was not covered yet when a given alu op is used in both "ptr_reg += reg" and "numeric_reg += reg" from different branches where we would incorrectly try to sanitize based on the pointer's limit. Catch this corner case and reject the program instead. Fixes: 979d63d50c0c ("bpf: prevent out of bounds speculation on pointer arithmetic") Reported-by: Jann Horn Signed-off-by: Daniel Borkmann Acked-by: Alexei Starovoitov Signed-off-by: Alexei Starovoitov --- include/linux/bpf_verifier.h | 1 + kernel/bpf/verifier.c | 61 ++++++++++++++++++++++++++++-------- 2 files changed, 49 insertions(+), 13 deletions(-) diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h index 27b74947cd2b..573cca00a0e6 100644 --- a/include/linux/bpf_verifier.h +++ b/include/linux/bpf_verifier.h @@ -172,6 +172,7 @@ struct bpf_verifier_state_list { #define BPF_ALU_SANITIZE_SRC 1U #define BPF_ALU_SANITIZE_DST 2U #define BPF_ALU_NEG_VALUE (1U << 2) +#define BPF_ALU_NON_POINTER (1U << 3) #define BPF_ALU_SANITIZE (BPF_ALU_SANITIZE_SRC | \ BPF_ALU_SANITIZE_DST) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index f6bc62a9ee8e..56674a7c3778 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -3103,6 +3103,40 @@ static int retrieve_ptr_limit(const struct bpf_reg_state *ptr_reg, } } +static bool can_skip_alu_sanitation(const struct bpf_verifier_env *env, + const struct bpf_insn *insn) +{ + return env->allow_ptr_leaks || BPF_SRC(insn->code) == BPF_K; +} + +static int update_alu_sanitation_state(struct bpf_insn_aux_data *aux, + u32 alu_state, u32 alu_limit) +{ + /* If we arrived here from different branches with different + * state or limits to sanitize, then this won't work. + */ + if (aux->alu_state && + (aux->alu_state != alu_state || + aux->alu_limit != alu_limit)) + return -EACCES; + + /* Corresponding fixup done in fixup_bpf_calls(). */ + aux->alu_state = alu_state; + aux->alu_limit = alu_limit; + return 0; +} + +static int sanitize_val_alu(struct bpf_verifier_env *env, + struct bpf_insn *insn) +{ + struct bpf_insn_aux_data *aux = cur_aux(env); + + if (can_skip_alu_sanitation(env, insn)) + return 0; + + return update_alu_sanitation_state(aux, BPF_ALU_NON_POINTER, 0); +} + static int sanitize_ptr_alu(struct bpf_verifier_env *env, struct bpf_insn *insn, const struct bpf_reg_state *ptr_reg, @@ -3117,7 +3151,7 @@ static int sanitize_ptr_alu(struct bpf_verifier_env *env, struct bpf_reg_state tmp; bool ret; - if (env->allow_ptr_leaks || BPF_SRC(insn->code) == BPF_K) + if (can_skip_alu_sanitation(env, insn)) return 0; /* We already marked aux for masking from non-speculative @@ -3133,19 +3167,8 @@ static int sanitize_ptr_alu(struct bpf_verifier_env *env, if (retrieve_ptr_limit(ptr_reg, &alu_limit, opcode, off_is_neg)) return 0; - - /* If we arrived here from different branches with different - * limits to sanitize, then this won't work. - */ - if (aux->alu_state && - (aux->alu_state != alu_state || - aux->alu_limit != alu_limit)) + if (update_alu_sanitation_state(aux, alu_state, alu_limit)) return -EACCES; - - /* Corresponding fixup done in fixup_bpf_calls(). */ - aux->alu_state = alu_state; - aux->alu_limit = alu_limit; - do_sim: /* Simulate and find potential out-of-bounds access under * speculative execution from truncation as a result of @@ -3418,6 +3441,8 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env, s64 smin_val, smax_val; u64 umin_val, umax_val; u64 insn_bitness = (BPF_CLASS(insn->code) == BPF_ALU64) ? 64 : 32; + u32 dst = insn->dst_reg; + int ret; if (insn_bitness == 32) { /* Relevant for 32-bit RSH: Information can propagate towards @@ -3452,6 +3477,11 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env, switch (opcode) { case BPF_ADD: + ret = sanitize_val_alu(env, insn); + if (ret < 0) { + verbose(env, "R%d tried to add from different pointers or scalars\n", dst); + return ret; + } if (signed_add_overflows(dst_reg->smin_value, smin_val) || signed_add_overflows(dst_reg->smax_value, smax_val)) { dst_reg->smin_value = S64_MIN; @@ -3471,6 +3501,11 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env, dst_reg->var_off = tnum_add(dst_reg->var_off, src_reg.var_off); break; case BPF_SUB: + ret = sanitize_val_alu(env, insn); + if (ret < 0) { + verbose(env, "R%d tried to sub from different pointers or scalars\n", dst); + return ret; + } if (signed_sub_overflows(dst_reg->smin_value, smax_val) || signed_sub_overflows(dst_reg->smax_value, smin_val)) { /* Overflow possible, we know nothing */ From 1cbbcfbbd56efd994d643428c69467fe3c8ab672 Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Sun, 6 Jan 2019 00:54:38 +0100 Subject: [PATCH 2/2] bpf: add various test cases for alu op on mixed dst register types Add couple of test_verifier tests to check sanitation of alu op insn with pointer and scalar type coming from different paths. This also includes BPF insns of the test reproducer provided by Jann Horn. Signed-off-by: Daniel Borkmann Acked-by: Alexei Starovoitov Signed-off-by: Alexei Starovoitov --- tools/testing/selftests/bpf/test_verifier.c | 120 ++++++++++++++++++++ 1 file changed, 120 insertions(+) diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c index 10d44446e801..2fd90d456892 100644 --- a/tools/testing/selftests/bpf/test_verifier.c +++ b/tools/testing/selftests/bpf/test_verifier.c @@ -6933,6 +6933,126 @@ static struct bpf_test tests[] = { .result = ACCEPT, .retval = 1, }, + { + "map access: mixing value pointer and scalar, 1", + .insns = { + // load map value pointer into r0 and r2 + BPF_MOV64_IMM(BPF_REG_0, 1), + BPF_LD_MAP_FD(BPF_REG_ARG1, 0), + BPF_MOV64_REG(BPF_REG_ARG2, BPF_REG_FP), + BPF_ALU64_IMM(BPF_ADD, BPF_REG_ARG2, -16), + BPF_ST_MEM(BPF_DW, BPF_REG_FP, -16, 0), + BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem), + BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 1), + BPF_EXIT_INSN(), + // load some number from the map into r1 + BPF_LDX_MEM(BPF_B, BPF_REG_1, BPF_REG_0, 0), + // depending on r1, branch: + BPF_JMP_IMM(BPF_JNE, BPF_REG_1, 0, 3), + // branch A + BPF_MOV64_REG(BPF_REG_2, BPF_REG_0), + BPF_MOV64_IMM(BPF_REG_3, 0), + BPF_JMP_A(2), + // branch B + BPF_MOV64_IMM(BPF_REG_2, 0), + BPF_MOV64_IMM(BPF_REG_3, 0x100000), + // common instruction + BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_3), + // depending on r1, branch: + BPF_JMP_IMM(BPF_JNE, BPF_REG_1, 0, 1), + // branch A + BPF_JMP_A(4), + // branch B + BPF_MOV64_IMM(BPF_REG_0, 0x13371337), + // verifier follows fall-through + BPF_JMP_IMM(BPF_JNE, BPF_REG_2, 0x100000, 2), + BPF_MOV64_IMM(BPF_REG_0, 0), + BPF_EXIT_INSN(), + // fake-dead code; targeted from branch A to + // prevent dead code sanitization + BPF_LDX_MEM(BPF_B, BPF_REG_0, BPF_REG_0, 0), + BPF_MOV64_IMM(BPF_REG_0, 0), + BPF_EXIT_INSN(), + }, + .fixup_map_array_48b = { 1 }, + .result = ACCEPT, + .result_unpriv = REJECT, + .errstr_unpriv = "R2 tried to add from different pointers or scalars", + .retval = 0, + }, + { + "map access: mixing value pointer and scalar, 2", + .insns = { + // load map value pointer into r0 and r2 + BPF_MOV64_IMM(BPF_REG_0, 1), + BPF_LD_MAP_FD(BPF_REG_ARG1, 0), + BPF_MOV64_REG(BPF_REG_ARG2, BPF_REG_FP), + BPF_ALU64_IMM(BPF_ADD, BPF_REG_ARG2, -16), + BPF_ST_MEM(BPF_DW, BPF_REG_FP, -16, 0), + BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem), + BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 1), + BPF_EXIT_INSN(), + // load some number from the map into r1 + BPF_LDX_MEM(BPF_B, BPF_REG_1, BPF_REG_0, 0), + // depending on r1, branch: + BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 0, 3), + // branch A + BPF_MOV64_IMM(BPF_REG_2, 0), + BPF_MOV64_IMM(BPF_REG_3, 0x100000), + BPF_JMP_A(2), + // branch B + BPF_MOV64_REG(BPF_REG_2, BPF_REG_0), + BPF_MOV64_IMM(BPF_REG_3, 0), + // common instruction + BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_3), + // depending on r1, branch: + BPF_JMP_IMM(BPF_JNE, BPF_REG_1, 0, 1), + // branch A + BPF_JMP_A(4), + // branch B + BPF_MOV64_IMM(BPF_REG_0, 0x13371337), + // verifier follows fall-through + BPF_JMP_IMM(BPF_JNE, BPF_REG_2, 0x100000, 2), + BPF_MOV64_IMM(BPF_REG_0, 0), + BPF_EXIT_INSN(), + // fake-dead code; targeted from branch A to + // prevent dead code sanitization + BPF_LDX_MEM(BPF_B, BPF_REG_0, BPF_REG_0, 0), + BPF_MOV64_IMM(BPF_REG_0, 0), + BPF_EXIT_INSN(), + }, + .fixup_map_array_48b = { 1 }, + .result = ACCEPT, + .result_unpriv = REJECT, + .errstr_unpriv = "R2 tried to add from different maps or paths", + .retval = 0, + }, + { + "sanitation: alu with different scalars", + .insns = { + BPF_MOV64_IMM(BPF_REG_0, 1), + BPF_LD_MAP_FD(BPF_REG_ARG1, 0), + BPF_MOV64_REG(BPF_REG_ARG2, BPF_REG_FP), + BPF_ALU64_IMM(BPF_ADD, BPF_REG_ARG2, -16), + BPF_ST_MEM(BPF_DW, BPF_REG_FP, -16, 0), + BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem), + BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 1), + BPF_EXIT_INSN(), + BPF_LDX_MEM(BPF_B, BPF_REG_1, BPF_REG_0, 0), + BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 0, 3), + BPF_MOV64_IMM(BPF_REG_2, 0), + BPF_MOV64_IMM(BPF_REG_3, 0x100000), + BPF_JMP_A(2), + BPF_MOV64_IMM(BPF_REG_2, 42), + BPF_MOV64_IMM(BPF_REG_3, 0x100001), + BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_3), + BPF_MOV64_REG(BPF_REG_0, BPF_REG_2), + BPF_EXIT_INSN(), + }, + .fixup_map_array_48b = { 1 }, + .result = ACCEPT, + .retval = 0x100000, + }, { "map access: value_ptr += known scalar, upper oob arith, test 1", .insns = {