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Date: Wed, 7 Jun 2017 15:58:50 +0100
From: Edward Cree <ecree@...arflare.com>
To: <davem@...emloft.net>,
Alexei Starovoitov <alexei.starovoitov@...il.com>,
Alexei Starovoitov <ast@...com>,
Daniel Borkmann <daniel@...earbox.net>
CC: <netdev@...r.kernel.org>,
iovisor-dev <iovisor-dev@...ts.iovisor.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: [RFC PATCH net-next 3/5] bpf/verifier: feed pointer-to-unknown-scalar
casts into scalar ALU path
If pointer leaks are allowed, and adjust_ptr_min_max_vals returns -EACCES,
treat the pointer as an unknown scalar and try again, because we might be
able to conclude something about the result (e.g. pointer & 0x40 is either
0 or 0x40).
Signed-off-by: Edward Cree <ecree@...arflare.com>
---
kernel/bpf/verifier.c | 244 ++++++++++++++++++++++++++------------------------
1 file changed, 127 insertions(+), 117 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index dd06e4e..1ff5b5d 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1566,6 +1566,8 @@ static void coerce_reg_to_32(struct bpf_reg_state *reg)
/* Handles arithmetic on a pointer and a scalar: computes new min/max and align.
* Caller must check_reg_overflow all argument regs beforehand.
* Caller should also handle BPF_MOV case separately.
+ * If we return -EACCES, caller may want to try again treating pointer as a
+ * scalar. So we only emit a diagnostic if !env->allow_ptr_leaks.
*/
static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env,
struct bpf_insn *insn,
@@ -1588,43 +1590,29 @@ 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) {
+ if (!env->allow_ptr_leaks)
verbose("R%d 32-bit pointer arithmetic prohibited\n",
dst);
- return -EACCES;
- }
- __mark_reg_unknown(dst_reg);
- /* High bits are known zero */
- dst_reg->align.mask = (u32)-1;
- return 0;
+ return -EACCES;
}
if (ptr_reg->type == PTR_TO_MAP_VALUE_OR_NULL) {
- if (!env->allow_ptr_leaks) {
+ if (!env->allow_ptr_leaks)
verbose("R%d pointer arithmetic on PTR_TO_MAP_VALUE_OR_NULL prohibited, null-check it first\n",
dst);
- return -EACCES;
- }
- __mark_reg_unknown(dst_reg);
- return 0;
+ return -EACCES;
}
if (ptr_reg->type == CONST_PTR_TO_MAP) {
- if (!env->allow_ptr_leaks) {
+ if (!env->allow_ptr_leaks)
verbose("R%d pointer arithmetic on CONST_PTR_TO_MAP prohibited\n",
dst);
- return -EACCES;
- }
- __mark_reg_unknown(dst_reg);
- return 0;
+ return -EACCES;
}
if (ptr_reg->type == PTR_TO_PACKET_END) {
- if (!env->allow_ptr_leaks) {
+ if (!env->allow_ptr_leaks)
verbose("R%d pointer arithmetic on PTR_TO_PACKET_END prohibited\n",
dst);
- return -EACCES;
- }
- __mark_reg_unknown(dst_reg);
- return 0;
+ return -EACCES;
}
/* In case of 'scalar += pointer', dst_reg inherits pointer type and id.
@@ -1648,8 +1636,9 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env,
break;
}
if (max_val == BPF_REGISTER_MAX_RANGE) {
- verbose("R%d tried to add unbounded value to pointer\n",
- dst);
+ if (!env->allow_ptr_leaks)
+ verbose("R%d tried to add unbounded value to pointer\n",
+ dst);
return -EACCES;
}
/* A new variable offset is created. Note that off_reg->off
@@ -1676,28 +1665,20 @@ 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) {
+ if (!env->allow_ptr_leaks)
verbose("R%d tried to subtract pointer from scalar\n",
dst);
- return -EACCES;
- }
- /* Make it an unknown scalar */
- __mark_reg_unknown(dst_reg);
- break;
+ return -EACCES;
}
/* We don't allow subtraction from FP, because (according to
* test_verifier.c test "invalid fp arithmetic", JITs might not
* be able to deal with it.
*/
if (ptr_reg->type == PTR_TO_STACK) {
- if (!env->allow_ptr_leaks) {
+ if (!env->allow_ptr_leaks)
verbose("R%d subtraction from stack pointer prohibited\n",
dst);
- return -EACCES;
- }
- /* Make it an unknown scalar */
- __mark_reg_unknown(dst_reg);
- break;
+ return -EACCES;
}
if (known && (ptr_reg->off - min_val ==
(s64)(s32)(ptr_reg->off - min_val))) {
@@ -1713,14 +1694,10 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env,
* This can happen if off_reg is an immediate.
*/
if ((s64)max_val < 0) {
- if (!env->allow_ptr_leaks) {
+ if (!env->allow_ptr_leaks)
verbose("R%d tried to subtract negative max_val %lld from pointer\n",
dst, (s64)max_val);
- return -EACCES;
- }
- /* Make it an unknown scalar */
- __mark_reg_unknown(dst_reg);
- break;
+ return -EACCES;
}
/* A new variable offset is created. If the subtrahend is known
* nonnegative, then any reg->range we had before is still good.
@@ -1747,99 +1724,37 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env,
* (However, in principle we could allow some cases, e.g.
* ptr &= ~3 which would reduce min_value by 3.)
*/
- if (!env->allow_ptr_leaks) {
+ if (!env->allow_ptr_leaks)
verbose("R%d bitwise operator %s on pointer prohibited\n",
dst, bpf_alu_string[opcode >> 4]);
- return -EACCES;
- }
- /* Make it an unknown scalar */
- __mark_reg_unknown(dst_reg);
+ return -EACCES;
default:
/* other operators (e.g. MUL,LSH) produce non-pointer results */
- if (!env->allow_ptr_leaks) {
+ if (!env->allow_ptr_leaks)
verbose("R%d pointer arithmetic with %s operator prohibited\n",
dst, bpf_alu_string[opcode >> 4]);
- return -EACCES;
- }
- /* Make it an unknown scalar */
- __mark_reg_unknown(dst_reg);
+ return -EACCES;
}
check_reg_overflow(dst_reg);
return 0;
}
-/* Handles ALU ops other than BPF_END, BPF_NEG and BPF_MOV: computes new min/max
- * and align.
- * TODO: check this is legit for ALU32, particularly around negatives
- */
-static int adjust_reg_min_max_vals(struct bpf_verifier_env *env,
- struct bpf_insn *insn)
+static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env,
+ struct bpf_insn *insn,
+ struct bpf_reg_state *dst_reg,
+ struct bpf_reg_state *src_reg)
{
- struct bpf_reg_state *regs = env->cur_state.regs, *dst_reg, *src_reg;
- struct bpf_reg_state *ptr_reg = NULL, off_reg = {0};
+ struct bpf_reg_state *regs = env->cur_state.regs;
s64 min_val = BPF_REGISTER_MIN_RANGE;
u64 max_val = BPF_REGISTER_MAX_RANGE;
u8 opcode = BPF_OP(insn->code);
bool src_known, dst_known;
- dst_reg = ®s[insn->dst_reg];
- check_reg_overflow(dst_reg);
- src_reg = NULL;
- if (dst_reg->type != SCALAR_VALUE)
- ptr_reg = dst_reg;
- if (BPF_SRC(insn->code) == BPF_X) {
- src_reg = ®s[insn->src_reg];
- check_reg_overflow(src_reg);
-
- if (src_reg->type != SCALAR_VALUE) {
- if (dst_reg->type != SCALAR_VALUE) {
- /* Combining two pointers by any ALU op yields
- * an arbitrary scalar.
- */
- if (!env->allow_ptr_leaks) {
- verbose("R%d pointer %s pointer prohibited\n",
- insn->dst_reg,
- bpf_alu_string[opcode >> 4]);
- return -EACCES;
- }
- mark_reg_unknown(regs, insn->dst_reg);
- return 0;
- } else {
- /* scalar += pointer
- * This is legal, but we have to reverse our
- * src/dest handling in computing the range
- */
- return adjust_ptr_min_max_vals(env, insn,
- src_reg, dst_reg);
- }
- } else if (ptr_reg) {
- /* pointer += scalar */
- 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
- * need to be able to read from this state.
- */
- off_reg.type = SCALAR_VALUE;
- off_reg.align = tn_const(insn->imm);
- off_reg.min_value = insn->imm;
- off_reg.max_value = insn->imm;
- src_reg = &off_reg;
- if (ptr_reg) /* pointer += K */
- return adjust_ptr_min_max_vals(env, insn,
- ptr_reg, src_reg);
- }
-
- /* Got here implies adding two SCALAR_VALUEs */
- if (WARN_ON_ONCE(ptr_reg)) {
- verbose("verifier internal error\n");
- return -EINVAL;
- }
- if (WARN_ON(!src_reg)) {
- verbose("verifier internal error\n");
- return -EINVAL;
+ 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);
}
if (BPF_CLASS(insn->code) != BPF_ALU64) {
/* 32-bit ALU ops are (32,32)->64 */
@@ -1990,6 +1905,101 @@ static int adjust_reg_min_max_vals(struct bpf_verifier_env *env,
return 0;
}
+/* Handles ALU ops other than BPF_END, BPF_NEG and BPF_MOV: computes new min/max
+ * and align.
+ */
+static int adjust_reg_min_max_vals(struct bpf_verifier_env *env,
+ struct bpf_insn *insn)
+{
+ struct bpf_reg_state *regs = env->cur_state.regs, *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];
+ check_reg_overflow(dst_reg);
+ src_reg = NULL;
+ if (dst_reg->type != SCALAR_VALUE)
+ ptr_reg = dst_reg;
+ if (BPF_SRC(insn->code) == BPF_X) {
+ src_reg = ®s[insn->src_reg];
+ check_reg_overflow(src_reg);
+
+ if (src_reg->type != SCALAR_VALUE) {
+ if (dst_reg->type != SCALAR_VALUE) {
+ /* Combining two pointers by any ALU op yields
+ * an arbitrary scalar.
+ */
+ if (!env->allow_ptr_leaks) {
+ verbose("R%d pointer %s pointer prohibited\n",
+ insn->dst_reg,
+ bpf_alu_string[opcode >> 4]);
+ return -EACCES;
+ }
+ mark_reg_unknown(regs, insn->dst_reg);
+ return 0;
+ } 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;
+ }
+ } 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;
+ }
+ } else {
+ /* Pretend the src is a reg with a known value, since we only
+ * need to be able to read from this state.
+ */
+ off_reg.type = SCALAR_VALUE;
+ off_reg.align = tn_const(insn->imm);
+ off_reg.min_value = insn->imm;
+ off_reg.max_value = 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;
+ }
+ }
+
+ /* Got here implies adding two SCALAR_VALUEs */
+ if (WARN_ON_ONCE(ptr_reg)) {
+ verbose("verifier internal error\n");
+ return -EINVAL;
+ }
+ if (WARN_ON(!src_reg)) {
+ verbose("verifier internal error\n");
+ return -EINVAL;
+ }
+ return adjust_scalar_min_max_vals(env, insn, dst_reg, src_reg);
+}
+
/* check validity of 32-bit and 64-bit arithmetic operations */
static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn)
{
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