diff options
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/bpf/verifier.c | 283 |
1 files changed, 166 insertions, 117 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index d4593571c404..04b24876cd23 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -1059,6 +1059,11 @@ static int check_ptr_alignment(struct bpf_verifier_env *env, break; case PTR_TO_STACK: pointer_desc = "stack "; + /* The stack spill tracking logic in check_stack_write() + * and check_stack_read() relies on stack accesses being + * aligned. + */ + strict = true; break; default: break; @@ -1067,6 +1072,29 @@ static int check_ptr_alignment(struct bpf_verifier_env *env, strict); } +/* truncate register to smaller size (in bytes) + * must be called with size < BPF_REG_SIZE + */ +static void coerce_reg_to_size(struct bpf_reg_state *reg, int size) +{ + u64 mask; + + /* clear high bits in bit representation */ + reg->var_off = tnum_cast(reg->var_off, size); + + /* fix arithmetic bounds */ + mask = ((u64)1 << (size * 8)) - 1; + if ((reg->umin_value & ~mask) == (reg->umax_value & ~mask)) { + reg->umin_value &= mask; + reg->umax_value &= mask; + } else { + reg->umin_value = 0; + reg->umax_value = mask; + } + reg->smin_value = reg->umin_value; + reg->smax_value = reg->umax_value; +} + /* check whether memory at (regno + off) is accessible for t = (read | write) * if t==write, value_regno is a register which value is stored into memory * if t==read, value_regno is a register which will receive the value from memory @@ -1200,9 +1228,7 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn if (!err && size < BPF_REG_SIZE && value_regno >= 0 && t == BPF_READ && regs[value_regno].type == SCALAR_VALUE) { /* b/h/w load zero-extends, mark upper bits as known 0 */ - regs[value_regno].var_off = - tnum_cast(regs[value_regno].var_off, size); - __update_reg_bounds(®s[value_regno]); + coerce_reg_to_size(®s[value_regno], size); } return err; } @@ -1282,6 +1308,7 @@ static int check_stack_boundary(struct bpf_verifier_env *env, int regno, tnum_strn(tn_buf, sizeof(tn_buf), regs[regno].var_off); verbose(env, "invalid variable stack read R%d var_off=%s\n", regno, tn_buf); + return -EACCES; } off = regs[regno].off + regs[regno].var_off.value; if (off >= 0 || off < -MAX_BPF_STACK || off + access_size > 0 || @@ -1674,7 +1701,13 @@ static int check_call(struct bpf_verifier_env *env, int func_id, int insn_idx) return -EINVAL; } + /* With LD_ABS/IND some JITs save/restore skb from r1. */ changes_data = bpf_helper_changes_pkt_data(fn->func); + if (changes_data && fn->arg1_type != ARG_PTR_TO_CTX) { + verbose(env, "kernel subsystem misconfigured func %s#%d: r1 != ctx\n", + func_id_name(func_id), func_id); + return -EINVAL; + } memset(&meta, 0, sizeof(meta)); meta.pkt_access = fn->pkt_access; @@ -1766,14 +1799,6 @@ static int check_call(struct bpf_verifier_env *env, int func_id, int insn_idx) return 0; } -static void coerce_reg_to_32(struct bpf_reg_state *reg) -{ - /* clear high 32 bits */ - reg->var_off = tnum_cast(reg->var_off, 4); - /* Update bounds */ - __update_reg_bounds(reg); -} - static bool signed_add_overflows(s64 a, s64 b) { /* Do the add in u64, where overflow is well-defined */ @@ -1794,6 +1819,41 @@ static bool signed_sub_overflows(s64 a, s64 b) return res > a; } +static bool check_reg_sane_offset(struct bpf_verifier_env *env, + const struct bpf_reg_state *reg, + enum bpf_reg_type type) +{ + bool known = tnum_is_const(reg->var_off); + s64 val = reg->var_off.value; + s64 smin = reg->smin_value; + + if (known && (val >= BPF_MAX_VAR_OFF || val <= -BPF_MAX_VAR_OFF)) { + verbose(env, "math between %s pointer and %lld is not allowed\n", + reg_type_str[type], val); + return false; + } + + if (reg->off >= BPF_MAX_VAR_OFF || reg->off <= -BPF_MAX_VAR_OFF) { + verbose(env, "%s pointer offset %d is not allowed\n", + reg_type_str[type], reg->off); + return false; + } + + if (smin == S64_MIN) { + verbose(env, "math between %s pointer and register with unbounded min value is not allowed\n", + reg_type_str[type]); + return false; + } + + if (smin >= BPF_MAX_VAR_OFF || smin <= -BPF_MAX_VAR_OFF) { + verbose(env, "value %lld makes %s pointer be out of bounds\n", + smin, reg_type_str[type]); + return false; + } + + return true; +} + /* Handles arithmetic on a pointer and a scalar: computes new min/max and var_off. * Caller should also handle BPF_MOV case separately. * If we return -EACCES, caller may want to try again treating pointer as a @@ -1830,29 +1890,25 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, if (BPF_CLASS(insn->code) != BPF_ALU64) { /* 32-bit ALU ops on pointers produce (meaningless) scalars */ - if (!env->allow_ptr_leaks) - verbose(env, - "R%d 32-bit pointer arithmetic prohibited\n", - dst); + verbose(env, + "R%d 32-bit pointer arithmetic prohibited\n", + dst); return -EACCES; } if (ptr_reg->type == PTR_TO_MAP_VALUE_OR_NULL) { - if (!env->allow_ptr_leaks) - verbose(env, "R%d pointer arithmetic on PTR_TO_MAP_VALUE_OR_NULL prohibited, null-check it first\n", - dst); + verbose(env, "R%d pointer arithmetic on PTR_TO_MAP_VALUE_OR_NULL prohibited, null-check it first\n", + dst); return -EACCES; } if (ptr_reg->type == CONST_PTR_TO_MAP) { - if (!env->allow_ptr_leaks) - verbose(env, "R%d pointer arithmetic on CONST_PTR_TO_MAP prohibited\n", - dst); + verbose(env, "R%d pointer arithmetic on CONST_PTR_TO_MAP prohibited\n", + dst); return -EACCES; } if (ptr_reg->type == PTR_TO_PACKET_END) { - if (!env->allow_ptr_leaks) - verbose(env, "R%d pointer arithmetic on PTR_TO_PACKET_END prohibited\n", - dst); + verbose(env, "R%d pointer arithmetic on PTR_TO_PACKET_END prohibited\n", + dst); return -EACCES; } @@ -1862,6 +1918,10 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, dst_reg->type = ptr_reg->type; dst_reg->id = ptr_reg->id; + if (!check_reg_sane_offset(env, off_reg, ptr_reg->type) || + !check_reg_sane_offset(env, ptr_reg, ptr_reg->type)) + return -EINVAL; + switch (opcode) { case BPF_ADD: /* We can take a fixed offset as long as it doesn't overflow @@ -1915,9 +1975,8 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, case BPF_SUB: if (dst_reg == off_reg) { /* scalar -= pointer. Creates an unknown scalar */ - if (!env->allow_ptr_leaks) - verbose(env, "R%d tried to subtract pointer from scalar\n", - dst); + verbose(env, "R%d tried to subtract pointer from scalar\n", + dst); return -EACCES; } /* We don't allow subtraction from FP, because (according to @@ -1925,9 +1984,8 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, * be able to deal with it. */ if (ptr_reg->type == PTR_TO_STACK) { - if (!env->allow_ptr_leaks) - verbose(env, "R%d subtraction from stack pointer prohibited\n", - dst); + verbose(env, "R%d subtraction from stack pointer prohibited\n", + dst); return -EACCES; } if (known && (ptr_reg->off - smin_val == @@ -1976,28 +2034,30 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, case BPF_AND: case BPF_OR: case BPF_XOR: - /* bitwise ops on pointers are troublesome, prohibit for now. - * (However, in principle we could allow some cases, e.g. - * ptr &= ~3 which would reduce min_value by 3.) - */ - if (!env->allow_ptr_leaks) - verbose(env, "R%d bitwise operator %s on pointer prohibited\n", - dst, bpf_alu_string[opcode >> 4]); + /* bitwise ops on pointers are troublesome, prohibit. */ + verbose(env, "R%d bitwise operator %s on pointer prohibited\n", + dst, bpf_alu_string[opcode >> 4]); return -EACCES; default: /* other operators (e.g. MUL,LSH) produce non-pointer results */ - if (!env->allow_ptr_leaks) - verbose(env, "R%d pointer arithmetic with %s operator prohibited\n", - dst, bpf_alu_string[opcode >> 4]); + verbose(env, "R%d pointer arithmetic with %s operator prohibited\n", + dst, bpf_alu_string[opcode >> 4]); return -EACCES; } + if (!check_reg_sane_offset(env, dst_reg, ptr_reg->type)) + return -EINVAL; + __update_reg_bounds(dst_reg); __reg_deduce_bounds(dst_reg); __reg_bound_offset(dst_reg); return 0; } +/* WARNING: This function does calculations on 64-bit values, but the actual + * execution may occur on 32-bit values. Therefore, things like bitshifts + * need extra checks in the 32-bit case. + */ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env, struct bpf_insn *insn, struct bpf_reg_state *dst_reg, @@ -2008,12 +2068,8 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env, bool src_known, dst_known; s64 smin_val, smax_val; u64 umin_val, umax_val; + u64 insn_bitness = (BPF_CLASS(insn->code) == BPF_ALU64) ? 64 : 32; - if (BPF_CLASS(insn->code) != BPF_ALU64) { - /* 32-bit ALU ops are (32,32)->64 */ - coerce_reg_to_32(dst_reg); - coerce_reg_to_32(&src_reg); - } smin_val = src_reg.smin_value; smax_val = src_reg.smax_value; umin_val = src_reg.umin_value; @@ -2021,6 +2077,12 @@ 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 && + opcode != BPF_ADD && opcode != BPF_SUB && opcode != BPF_AND) { + __mark_reg_unknown(dst_reg); + return 0; + } + switch (opcode) { case BPF_ADD: if (signed_add_overflows(dst_reg->smin_value, smin_val) || @@ -2149,9 +2211,9 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env, __update_reg_bounds(dst_reg); break; case BPF_LSH: - if (umax_val > 63) { - /* Shifts greater than 63 are undefined. This includes - * shifts by a negative number. + if (umax_val >= insn_bitness) { + /* Shifts greater than 31 or 63 are undefined. + * This includes shifts by a negative number. */ mark_reg_unknown(env, regs, insn->dst_reg); break; @@ -2177,27 +2239,29 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env, __update_reg_bounds(dst_reg); break; case BPF_RSH: - if (umax_val > 63) { - /* Shifts greater than 63 are undefined. This includes - * shifts by a negative number. + if (umax_val >= insn_bitness) { + /* Shifts greater than 31 or 63 are undefined. + * This includes shifts by a negative number. */ mark_reg_unknown(env, regs, insn->dst_reg); break; } - /* BPF_RSH is an unsigned shift, so make the appropriate casts */ - if (dst_reg->smin_value < 0) { - if (umin_val) { - /* Sign bit will be cleared */ - dst_reg->smin_value = 0; - } else { - /* Lost sign bit information */ - dst_reg->smin_value = S64_MIN; - dst_reg->smax_value = S64_MAX; - } - } else { - dst_reg->smin_value = - (u64)(dst_reg->smin_value) >> umax_val; - } + /* BPF_RSH is an unsigned shift. If the value in dst_reg might + * be negative, then either: + * 1) src_reg might be zero, so the sign bit of the result is + * unknown, so we lose our signed bounds + * 2) it's known negative, thus the unsigned bounds capture the + * signed bounds + * 3) the signed bounds cross zero, so they tell us nothing + * about the result + * If the value in dst_reg is known nonnegative, then again the + * unsigned bounts capture the signed bounds. + * Thus, in all cases it suffices to blow away our signed bounds + * and rely on inferring new ones from the unsigned bounds and + * var_off of the result. + */ + dst_reg->smin_value = S64_MIN; + dst_reg->smax_value = S64_MAX; if (src_known) dst_reg->var_off = tnum_rshift(dst_reg->var_off, umin_val); @@ -2213,6 +2277,12 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env, break; } + if (BPF_CLASS(insn->code) != BPF_ALU64) { + /* 32-bit ALU ops are (32,32)->32 */ + coerce_reg_to_size(dst_reg, 4); + coerce_reg_to_size(&src_reg, 4); + } + __reg_deduce_bounds(dst_reg); __reg_bound_offset(dst_reg); return 0; @@ -2227,7 +2297,6 @@ static int adjust_reg_min_max_vals(struct bpf_verifier_env *env, struct bpf_reg_state *regs = cur_regs(env), *dst_reg, *src_reg; struct bpf_reg_state *ptr_reg = NULL, off_reg = {0}; u8 opcode = BPF_OP(insn->code); - int rc; dst_reg = ®s[insn->dst_reg]; src_reg = NULL; @@ -2238,43 +2307,29 @@ static int adjust_reg_min_max_vals(struct bpf_verifier_env *env, if (src_reg->type != SCALAR_VALUE) { if (dst_reg->type != SCALAR_VALUE) { /* Combining two pointers by any ALU op yields - * an arbitrary scalar. + * an arbitrary scalar. Disallow all math except + * pointer subtraction */ - if (!env->allow_ptr_leaks) { - verbose(env, "R%d pointer %s pointer prohibited\n", - insn->dst_reg, - bpf_alu_string[opcode >> 4]); - return -EACCES; + if (opcode == BPF_SUB){ + mark_reg_unknown(env, regs, insn->dst_reg); + return 0; } - mark_reg_unknown(env, regs, insn->dst_reg); - return 0; + verbose(env, "R%d pointer %s pointer prohibited\n", + insn->dst_reg, + bpf_alu_string[opcode >> 4]); + return -EACCES; } else { /* scalar += pointer * This is legal, but we have to reverse our * src/dest handling in computing the range */ - rc = adjust_ptr_min_max_vals(env, insn, - src_reg, dst_reg); - if (rc == -EACCES && env->allow_ptr_leaks) { - /* scalar += unknown scalar */ - __mark_reg_unknown(&off_reg); - return adjust_scalar_min_max_vals( - env, insn, - dst_reg, off_reg); - } - return rc; + return adjust_ptr_min_max_vals(env, insn, + src_reg, dst_reg); } } else if (ptr_reg) { /* pointer += scalar */ - rc = adjust_ptr_min_max_vals(env, insn, - dst_reg, src_reg); - if (rc == -EACCES && env->allow_ptr_leaks) { - /* unknown scalar += scalar */ - __mark_reg_unknown(dst_reg); - return adjust_scalar_min_max_vals( - env, insn, dst_reg, *src_reg); - } - return rc; + return adjust_ptr_min_max_vals(env, insn, + dst_reg, src_reg); } } else { /* Pretend the src is a reg with a known value, since we only @@ -2283,17 +2338,9 @@ static int adjust_reg_min_max_vals(struct bpf_verifier_env *env, off_reg.type = SCALAR_VALUE; __mark_reg_known(&off_reg, insn->imm); src_reg = &off_reg; - if (ptr_reg) { /* pointer += K */ - rc = adjust_ptr_min_max_vals(env, insn, - ptr_reg, src_reg); - if (rc == -EACCES && env->allow_ptr_leaks) { - /* unknown scalar += K */ - __mark_reg_unknown(dst_reg); - return adjust_scalar_min_max_vals( - env, insn, dst_reg, off_reg); - } - return rc; - } + if (ptr_reg) /* pointer += K */ + return adjust_ptr_min_max_vals(env, insn, + ptr_reg, src_reg); } /* Got here implies adding two SCALAR_VALUEs */ @@ -2390,17 +2437,20 @@ static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn) return -EACCES; } mark_reg_unknown(env, regs, insn->dst_reg); - /* high 32 bits are known zero. */ - regs[insn->dst_reg].var_off = tnum_cast( - regs[insn->dst_reg].var_off, 4); - __update_reg_bounds(®s[insn->dst_reg]); + coerce_reg_to_size(®s[insn->dst_reg], 4); } } else { /* case: R = imm * remember the value we stored into this reg */ regs[insn->dst_reg].type = SCALAR_VALUE; - __mark_reg_known(regs + insn->dst_reg, insn->imm); + if (BPF_CLASS(insn->code) == BPF_ALU64) { + __mark_reg_known(regs + insn->dst_reg, + insn->imm); + } else { + __mark_reg_known(regs + insn->dst_reg, + (u32)insn->imm); + } } } else if (opcode > BPF_END) { @@ -3431,15 +3481,14 @@ static bool regsafe(struct bpf_reg_state *rold, struct bpf_reg_state *rcur, return range_within(rold, rcur) && tnum_in(rold->var_off, rcur->var_off); } else { - /* if we knew anything about the old value, we're not - * equal, because we can't know anything about the - * scalar value of the pointer in the new value. + /* We're trying to use a pointer in place of a scalar. + * Even if the scalar was unbounded, this could lead to + * pointer leaks because scalars are allowed to leak + * while pointers are not. We could make this safe in + * special cases if root is calling us, but it's + * probably not worth the hassle. */ - return rold->umin_value == 0 && - rold->umax_value == U64_MAX && - rold->smin_value == S64_MIN && - rold->smax_value == S64_MAX && - tnum_is_unknown(rold->var_off); + return false; } case PTR_TO_MAP_VALUE: /* If the new min/max/var_off satisfy the old ones and |