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Date: Wed, 7 Jun 2017 19:35:42 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Edward Cree <ecree@...arflare.com>
Cc: davem@...emloft.net, Alexei Starovoitov <ast@...com>,
Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org,
iovisor-dev <iovisor-dev@...ts.iovisor.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH net-next 3/5] bpf/verifier: feed
pointer-to-unknown-scalar casts into scalar ALU path
On Wed, Jun 07, 2017 at 03:58:50PM +0100, Edward Cree wrote:
> 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;
such large back and forth move doesn't help reviewing.
may be just merge it into previous patch?
Or keep that function in the right place in patch 2 already?
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