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authorAlexei Starovoitov <ast@kernel.org>2018-12-03 22:46:05 -0800
committerDaniel Borkmann <daniel@iogearbox.net>2018-12-04 17:22:02 +0100
commit4f7b3e82589e0de723780198ec7983e427144c0a (patch)
tree38fa3a5035551cfe6b4e5d7d5268ca4834e353f5 /kernel
parentc3494801cd1785e2c25f1a5735fa19ddcf9665da (diff)
bpf: improve verifier branch analysis
pathological bpf programs may try to force verifier to explode in the number of branch states: 20: (d5) if r1 s<= 0x24000028 goto pc+0 21: (b5) if r0 <= 0xe1fa20 goto pc+2 22: (d5) if r1 s<= 0x7e goto pc+0 23: (b5) if r0 <= 0xe880e000 goto pc+0 24: (c5) if r0 s< 0x2100ecf4 goto pc+0 25: (d5) if r1 s<= 0xe880e000 goto pc+1 26: (c5) if r0 s< 0xf4041810 goto pc+0 27: (d5) if r1 s<= 0x1e007e goto pc+0 28: (b5) if r0 <= 0xe86be000 goto pc+0 29: (07) r0 += 16614 30: (c5) if r0 s< 0x6d0020da goto pc+0 31: (35) if r0 >= 0x2100ecf4 goto pc+0 Teach verifier to recognize always taken and always not taken branches. This analysis is already done for == and != comparison. Expand it to all other branches. It also helps real bpf programs to be verified faster: before after bpf_lb-DLB_L3.o 2003 1940 bpf_lb-DLB_L4.o 3173 3089 bpf_lb-DUNKNOWN.o 1080 1065 bpf_lxc-DDROP_ALL.o 29584 28052 bpf_lxc-DUNKNOWN.o 36916 35487 bpf_netdev.o 11188 10864 bpf_overlay.o 6679 6643 bpf_lcx_jit.o 39555 38437 Reported-by: Anatoly Trosinenko <anatoly.trosinenko@gmail.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Edward Cree <ecree@solarflare.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/bpf/verifier.c93
1 files changed, 80 insertions, 13 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 751bb30b7c5c..55a49703f423 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3751,6 +3751,79 @@ static void find_good_pkt_pointers(struct bpf_verifier_state *vstate,
}
}
+/* compute branch direction of the expression "if (reg opcode val) goto target;"
+ * and return:
+ * 1 - branch will be taken and "goto target" will be executed
+ * 0 - branch will not be taken and fall-through to next insn
+ * -1 - unknown. Example: "if (reg < 5)" is unknown when register value range [0,10]
+ */
+static int is_branch_taken(struct bpf_reg_state *reg, u64 val, u8 opcode)
+{
+ if (__is_pointer_value(false, reg))
+ return -1;
+
+ switch (opcode) {
+ case BPF_JEQ:
+ if (tnum_is_const(reg->var_off))
+ return !!tnum_equals_const(reg->var_off, val);
+ break;
+ case BPF_JNE:
+ if (tnum_is_const(reg->var_off))
+ return !tnum_equals_const(reg->var_off, val);
+ break;
+ case BPF_JGT:
+ if (reg->umin_value > val)
+ return 1;
+ else if (reg->umax_value <= val)
+ return 0;
+ break;
+ case BPF_JSGT:
+ if (reg->smin_value > (s64)val)
+ return 1;
+ else if (reg->smax_value < (s64)val)
+ return 0;
+ break;
+ case BPF_JLT:
+ if (reg->umax_value < val)
+ return 1;
+ else if (reg->umin_value >= val)
+ return 0;
+ break;
+ case BPF_JSLT:
+ if (reg->smax_value < (s64)val)
+ return 1;
+ else if (reg->smin_value >= (s64)val)
+ return 0;
+ break;
+ case BPF_JGE:
+ if (reg->umin_value >= val)
+ return 1;
+ else if (reg->umax_value < val)
+ return 0;
+ break;
+ case BPF_JSGE:
+ if (reg->smin_value >= (s64)val)
+ return 1;
+ else if (reg->smax_value < (s64)val)
+ return 0;
+ break;
+ case BPF_JLE:
+ if (reg->umax_value <= val)
+ return 1;
+ else if (reg->umin_value > val)
+ return 0;
+ break;
+ case BPF_JSLE:
+ if (reg->smax_value <= (s64)val)
+ return 1;
+ else if (reg->smin_value > (s64)val)
+ return 0;
+ break;
+ }
+
+ return -1;
+}
+
/* Adjusts the register min/max values in the case that the dst_reg is the
* variable register that we are working on, and src_reg is a constant or we're
* simply doing a BPF_K check.
@@ -4152,21 +4225,15 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env,
dst_reg = &regs[insn->dst_reg];
- /* detect if R == 0 where R was initialized to zero earlier */
- if (BPF_SRC(insn->code) == BPF_K &&
- (opcode == BPF_JEQ || opcode == BPF_JNE) &&
- dst_reg->type == SCALAR_VALUE &&
- tnum_is_const(dst_reg->var_off)) {
- if ((opcode == BPF_JEQ && dst_reg->var_off.value == insn->imm) ||
- (opcode == BPF_JNE && dst_reg->var_off.value != insn->imm)) {
- /* if (imm == imm) goto pc+off;
- * only follow the goto, ignore fall-through
- */
+ if (BPF_SRC(insn->code) == BPF_K) {
+ int pred = is_branch_taken(dst_reg, insn->imm, opcode);
+
+ if (pred == 1) {
+ /* only follow the goto, ignore fall-through */
*insn_idx += insn->off;
return 0;
- } else {
- /* if (imm != imm) goto pc+off;
- * only follow fall-through branch, since
+ } else if (pred == 0) {
+ /* only follow fall-through branch, since
* that's where the program will go
*/
return 0;