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Commit b4e432f1 authored by Daniel Borkmann's avatar Daniel Borkmann Committed by David S. Miller
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bpf: enable BPF_J{LT, LE, SLT, SLE} opcodes in verifier 

Enable the newly added jump opcodes, main parts are in two
different areas, namely direct packet access and dynamic map
value access. For the direct packet access, we now allow for
the following two new patterns to match in order to trigger
markings with find_good_pkt_pointers():

Variant 1 (access ok when taking the branch):

  0: (61) r2 = *(u32 *)(r1 +76)
  1: (61) r3 = *(u32 *)(r1 +80)
  2: (bf) r0 = r2
  3: (07) r0 += 8
  4: (ad) if r0 < r3 goto pc+2
  R0=pkt(id=0,off=8,r=0) R1=ctx R2=pkt(id=0,off=0,r=0)
  R3=pkt_end R10=fp
  5: (b7) r0 = 0
  6: (95) exit

  from 4 to 7: R0=pkt(id=0,off=8,r=8) R1=ctx
               R2=pkt(id=0,off=0,r=8) R3=pkt_end R10=fp
  7: (71) r0 = *(u8 *)(r2 +0)
  8: (05) goto pc-4
  5: (b7) r0 = 0
  6: (95) exit
  processed 11 insns, stack depth 0

Variant 2 (access ok on fall-through):

  0: (61) r2 = *(u32 *)(r1 +76)
  1: (61) r3 = *(u32 *)(r1 +80)
  2: (bf) r0 = r2
  3: (07) r0 += 8
  4: (bd) if r3 <= r0 goto pc+1
  R0=pkt(id=0,off=8,r=8) R1=ctx R2=pkt(id=0,off=0,r=8)
  R3=pkt_end R10=fp
  5: (71) r0 = *(u8 *)(r2 +0)
  6: (b7) r0 = 1
  7: (95) exit

  from 4 to 6: R0=pkt(id=0,off=8,r=0) R1=ctx
               R2=pkt(id=0,off=0,r=0) R3=pkt_end R10=fp
  6: (b7) r0 = 1
  7: (95) exit
  processed 10 insns, stack depth 0

The above two basically just swap the branches where we need
to handle an exception and allow packet access compared to the
two already existing variants for find_good_pkt_pointers().

For the dynamic map value access, we add the new instructions
to reg_set_min_max() and reg_set_min_max_inv() in order to
learn bounds. Verifier test cases for both are added in a
follow-up patch.
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarJohn Fastabend <john.fastabend@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 5dd294d4
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Showing with 58 additions and 4 deletions
kernel/bpf/verifier.c
View file @ b4e432f1
......@@ -312,11 +312,15 @@ static const char *const bpf_jmp_string[16] = {
[BPF_JA >> 4] = "jmp",
[BPF_JEQ >> 4] = "==",
[BPF_JGT >> 4] = ">",
[BPF_JLT >> 4] = "<",
[BPF_JGE >> 4] = ">=",
[BPF_JLE >> 4] = "<=",
[BPF_JSET >> 4] = "&",
[BPF_JNE >> 4] = "!=",
[BPF_JSGT >> 4] = "s>",
[BPF_JSLT >> 4] = "s<",
[BPF_JSGE >> 4] = "s>=",
[BPF_JSLE >> 4] = "s<=",
[BPF_CALL >> 4] = "call",
[BPF_EXIT >> 4] = "exit",
};
......@@ -2383,27 +2387,37 @@ static void find_good_pkt_pointers(struct bpf_verifier_state *state,
*/
return;
/* LLVM can generate two kind of checks:
/* LLVM can generate four kind of checks:
*
* Type 1:
* Type 1/2:
*
* r2 = r3;
* r2 += 8;
* if (r2 > pkt_end) goto <handle exception>
* <access okay>
*
* r2 = r3;
* r2 += 8;
* if (r2 < pkt_end) goto <access okay>
* <handle exception>
*
* Where:
* r2 == dst_reg, pkt_end == src_reg
* r2=pkt(id=n,off=8,r=0)
* r3=pkt(id=n,off=0,r=0)
*
* Type 2:
* Type 3/4:
*
* r2 = r3;
* r2 += 8;
* if (pkt_end >= r2) goto <access okay>
* <handle exception>
*
* r2 = r3;
* r2 += 8;
* if (pkt_end <= r2) goto <handle exception>
* <access okay>
*
* Where:
* pkt_end == dst_reg, r2 == src_reg
* r2=pkt(id=n,off=8,r=0)
......@@ -2471,6 +2485,14 @@ static void reg_set_min_max(struct bpf_reg_state *true_reg,
false_reg->smax_value = min_t(s64, false_reg->smax_value, val);
true_reg->smin_value = max_t(s64, true_reg->smin_value, val + 1);
break;
case BPF_JLT:
false_reg->umin_value = max(false_reg->umin_value, val);
true_reg->umax_value = min(true_reg->umax_value, val - 1);
break;
case BPF_JSLT:
false_reg->smin_value = max_t(s64, false_reg->smin_value, val);
true_reg->smax_value = min_t(s64, true_reg->smax_value, val - 1);
break;
case BPF_JGE:
false_reg->umax_value = min(false_reg->umax_value, val - 1);
true_reg->umin_value = max(true_reg->umin_value, val);
......@@ -2479,6 +2501,14 @@ static void reg_set_min_max(struct bpf_reg_state *true_reg,
false_reg->smax_value = min_t(s64, false_reg->smax_value, val - 1);
true_reg->smin_value = max_t(s64, true_reg->smin_value, val);
break;
case BPF_JLE:
false_reg->umin_value = max(false_reg->umin_value, val + 1);
true_reg->umax_value = min(true_reg->umax_value, val);
break;
case BPF_JSLE:
false_reg->smin_value = max_t(s64, false_reg->smin_value, val + 1);
true_reg->smax_value = min_t(s64, true_reg->smax_value, val);
break;
default:
break;
}
......@@ -2527,6 +2557,14 @@ static void reg_set_min_max_inv(struct bpf_reg_state *true_reg,
true_reg->smax_value = min_t(s64, true_reg->smax_value, val - 1);
false_reg->smin_value = max_t(s64, false_reg->smin_value, val);
break;
case BPF_JLT:
true_reg->umin_value = max(true_reg->umin_value, val + 1);
false_reg->umax_value = min(false_reg->umax_value, val);
break;
case BPF_JSLT:
true_reg->smin_value = max_t(s64, true_reg->smin_value, val + 1);
false_reg->smax_value = min_t(s64, false_reg->smax_value, val);
break;
case BPF_JGE:
true_reg->umax_value = min(true_reg->umax_value, val);
false_reg->umin_value = max(false_reg->umin_value, val + 1);
......@@ -2535,6 +2573,14 @@ static void reg_set_min_max_inv(struct bpf_reg_state *true_reg,
true_reg->smax_value = min_t(s64, true_reg->smax_value, val);
false_reg->smin_value = max_t(s64, false_reg->smin_value, val + 1);
break;
case BPF_JLE:
true_reg->umin_value = max(true_reg->umin_value, val);
false_reg->umax_value = min(false_reg->umax_value, val - 1);
break;
case BPF_JSLE:
true_reg->smin_value = max_t(s64, true_reg->smin_value, val);
false_reg->smax_value = min_t(s64, false_reg->smax_value, val - 1);
break;
default:
break;
}
......@@ -2659,7 +2705,7 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env,
u8 opcode = BPF_OP(insn->code);
int err;
if (opcode > BPF_EXIT) {
if (opcode > BPF_JSLE) {
verbose("invalid BPF_JMP opcode %x\n", opcode);
return -EINVAL;
}
......@@ -2761,10 +2807,18 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env,
dst_reg->type == PTR_TO_PACKET &&
regs[insn->src_reg].type == PTR_TO_PACKET_END) {
find_good_pkt_pointers(this_branch, dst_reg);
} else if (BPF_SRC(insn->code) == BPF_X && opcode == BPF_JLT &&
dst_reg->type == PTR_TO_PACKET &&
regs[insn->src_reg].type == PTR_TO_PACKET_END) {
find_good_pkt_pointers(other_branch, dst_reg);
} else if (BPF_SRC(insn->code) == BPF_X && opcode == BPF_JGE &&
dst_reg->type == PTR_TO_PACKET_END &&
regs[insn->src_reg].type == PTR_TO_PACKET) {
find_good_pkt_pointers(other_branch, &regs[insn->src_reg]);
} else if (BPF_SRC(insn->code) == BPF_X && opcode == BPF_JLE &&
dst_reg->type == PTR_TO_PACKET_END &&
regs[insn->src_reg].type == PTR_TO_PACKET) {
find_good_pkt_pointers(this_branch, &regs[insn->src_reg]);
} else if (is_pointer_value(env, insn->dst_reg)) {
verbose("R%d pointer comparison prohibited\n", insn->dst_reg);
return -EACCES;
......
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