aboutsummaryrefslogtreecommitdiffstats
path: root/kernel/bpf/verifier.c
diff options
context:
space:
mode:
Diffstat (limited to 'kernel/bpf/verifier.c')
-rw-r--r--kernel/bpf/verifier.c283
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(&regs[value_regno]);
+ coerce_reg_to_size(&regs[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 = &regs[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(&regs[insn->dst_reg]);
+ coerce_reg_to_size(&regs[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
Copyright © 1996 – 2023 Jason A. Donenfeld. All Rights Reverse Engineered.