From: Alexei Starovoitov <ast@xxxxxxxxxx>
Introduce may_goto instruction that acts on a hidden bpf_iter_num, so that
bpf_iter_num_new(), bpf_iter_num_destroy() don't need to be called explicitly.
It can be used in any normal "for" or "while" loop, like
for (i = zero; i < cnt; cond_break, i++) {
The verifier recognizes that may_goto is used in the program,
reserves additional 8 bytes of stack, initializes them in subprog
prologue, and replaces may_goto instruction with:
aux_reg = *(u64 *)(fp - 40)
if aux_reg == 0 goto pc+off
aux_reg += 1
*(u64 *)(fp - 40) = aux_reg
may_goto instruction can be used by LLVM to implement __builtin_memcpy,
__builtin_strcmp.
may_goto is not a full substitute for bpf_for() macro.
bpf_for() doesn't have induction variable that verifiers sees,
so 'i' in bpf_for(i, 0, 100) is seen as imprecise and bounded.
But when the code is written as:
for (i = 0; i < 100; cond_break, i++)
the verifier see 'i' as precise constant zero,
hence cond_break (aka may_goto) doesn't help to converge the loop.
A static or global variable can be used as a workaround:
static int zero = 0;
for (i = zero; i < 100; cond_break, i++) // works!
may_goto works well with arena pointers that don't need to be bounds-checked
on every iteration. Load/store from arena returns imprecise unbounded scalars.
Reserve new opcode BPF_JMP | BPF_JMA for may_goto insn.
JMA stands for "jump maybe", and "jump multipurpose", and "jump multi always".
Since goto_or_nop insn was proposed, it may use the same opcode.
may_goto vs goto_or_nop can be distinguished by src_reg:
code = BPF_JMP | BPF_JMA:
src_reg = 0 - may_goto
src_reg = 1 - goto_or_nop
We could have reused BPF_JMP | BPF_JA like:
src_reg = 0 - normal goto
src_reg = 1 - may_goto
src_reg = 2 - goto_or_nop
but JA is a real insn and it's unconditional, while may_goto and goto_or_nop
are pseudo instructions, and both are conditional. Hence it's better to
have a different opcode for them. Hence BPF_JMA.
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
---
include/linux/bpf_verifier.h | 2 +
include/uapi/linux/bpf.h | 1 +
kernel/bpf/core.c | 1 +
kernel/bpf/disasm.c | 3 +
kernel/bpf/verifier.c | 156 ++++++++++++++++++++++++++-------
tools/include/uapi/linux/bpf.h | 1 +
6 files changed, 134 insertions(+), 30 deletions(-)
diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 84365e6dd85d..917ca603059b 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -449,6 +449,7 @@ struct bpf_verifier_state {
u32 jmp_history_cnt;
u32 dfs_depth;
u32 callback_unroll_depth;
+ u32 may_goto_cnt;
};
#define bpf_get_spilled_reg(slot, frame, mask) \
@@ -619,6 +620,7 @@ struct bpf_subprog_info {
u32 start; /* insn idx of function entry point */
u32 linfo_idx; /* The idx to the main_prog->aux->linfo */
u16 stack_depth; /* max. stack depth used by this function */
+ u16 stack_extra;
bool has_tail_call: 1;
bool tail_call_reachable: 1;
bool has_ld_abs: 1;
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index a241f407c234..932ffef0dc88 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -42,6 +42,7 @@
#define BPF_JSGE 0x70 /* SGE is signed '>=', GE in x86 */
#define BPF_JSLT 0xc0 /* SLT is signed, '<' */
#define BPF_JSLE 0xd0 /* SLE is signed, '<=' */
+#define BPF_JMA 0xe0 /* may_goto */
#define BPF_CALL 0x80 /* function call */
#define BPF_EXIT 0x90 /* function return */
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 71c459a51d9e..ba6101447b49 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1675,6 +1675,7 @@ bool bpf_opcode_in_insntable(u8 code)
[BPF_LD | BPF_IND | BPF_B] = true,
[BPF_LD | BPF_IND | BPF_H] = true,
[BPF_LD | BPF_IND | BPF_W] = true,
+ [BPF_JMP | BPF_JMA] = true,
};
#undef BPF_INSN_3_TBL
#undef BPF_INSN_2_TBL
diff --git a/kernel/bpf/disasm.c b/kernel/bpf/disasm.c
index 49940c26a227..598cd38af84c 100644
--- a/kernel/bpf/disasm.c
+++ b/kernel/bpf/disasm.c
@@ -322,6 +322,9 @@ void print_bpf_insn(const struct bpf_insn_cbs *cbs,
} else if (insn->code == (BPF_JMP | BPF_JA)) {
verbose(cbs->private_data, "(%02x) goto pc%+d\n",
insn->code, insn->off);
+ } else if (insn->code == (BPF_JMP | BPF_JMA)) {
+ verbose(cbs->private_data, "(%02x) may_goto pc%+d\n",
+ insn->code, insn->off);
} else if (insn->code == (BPF_JMP32 | BPF_JA)) {
verbose(cbs->private_data, "(%02x) gotol pc%+d\n",
insn->code, insn->imm);
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 4dd84e13bbfe..226bb65f9c2c 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1429,6 +1429,7 @@ static int copy_verifier_state(struct bpf_verifier_state *dst_state,
dst_state->dfs_depth = src->dfs_depth;
dst_state->callback_unroll_depth = src->callback_unroll_depth;
dst_state->used_as_loop_entry = src->used_as_loop_entry;
+ dst_state->may_goto_cnt = src->may_goto_cnt;
for (i = 0; i <= src->curframe; i++) {
dst = dst_state->frame[i];
if (!dst) {
@@ -7880,6 +7881,11 @@ static int widen_imprecise_scalars(struct bpf_verifier_env *env,
return 0;
}
+static bool is_may_goto_insn(struct bpf_verifier_env *env, int insn_idx)
+{
+ return env->prog->insnsi[insn_idx].code == (BPF_JMP | BPF_JMA);
+}
+
/* process_iter_next_call() is called when verifier gets to iterator's next
* "method" (e.g., bpf_iter_num_next() for numbers iterator) call. We'll refer
* to it as just "iter_next()" in comments below.
@@ -14871,11 +14877,35 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env,
int err;
/* Only conditional jumps are expected to reach here. */
- if (opcode == BPF_JA || opcode > BPF_JSLE) {
+ if (opcode == BPF_JA || opcode > BPF_JMA) {
verbose(env, "invalid BPF_JMP/JMP32 opcode %x\n", opcode);
return -EINVAL;
}
+ if (opcode == BPF_JMA) {
+ struct bpf_verifier_state *cur_st = env->cur_state, *queued_st, *prev_st;
+ int idx = *insn_idx;
+
+ if (insn->code != (BPF_JMP | BPF_JMA) ||
+ insn->src_reg || insn->dst_reg || insn->imm || insn->off == 0) {
+ verbose(env, "invalid may_goto off %d imm %d\n",
+ insn->off, insn->imm);
+ return -EINVAL;
+ }
+ prev_st = find_prev_entry(env, cur_st->parent, idx);
+
+ /* branch out 'fallthrough' insn as a new state to explore */
+ queued_st = push_stack(env, idx + 1, idx, false);
+ if (!queued_st)
+ return -ENOMEM;
+
+ queued_st->may_goto_cnt++;
+ if (prev_st)
+ widen_imprecise_scalars(env, prev_st, queued_st);
+ *insn_idx += insn->off;
+ return 0;
+ }
+
/* check src2 operand */
err = check_reg_arg(env, insn->dst_reg, SRC_OP);
if (err)
@@ -15659,6 +15689,8 @@ static int visit_insn(int t, struct bpf_verifier_env *env)
default:
/* conditional jump with two edges */
mark_prune_point(env, t);
+ if (insn->code == (BPF_JMP | BPF_JMA))
+ mark_force_checkpoint(env, t);
ret = push_insn(t, t + 1, FALLTHROUGH, env);
if (ret)
@@ -17135,6 +17167,13 @@ static int is_state_visited(struct bpf_verifier_env *env, int insn_idx)
}
goto skip_inf_loop_check;
}
+ if (is_may_goto_insn(env, insn_idx)) {
+ if (states_equal(env, &sl->state, cur, true)) {
+ update_loop_entry(cur, &sl->state);
+ goto hit;
+ }
+ goto skip_inf_loop_check;
+ }
if (calls_callback(env, insn_idx)) {
if (states_equal(env, &sl->state, cur, true))
goto hit;
@@ -17144,6 +17183,7 @@ static int is_state_visited(struct bpf_verifier_env *env, int insn_idx)
if (states_maybe_looping(&sl->state, cur) &&
states_equal(env, &sl->state, cur, true) &&
!iter_active_depths_differ(&sl->state, cur) &&
+ sl->state.may_goto_cnt == cur->may_goto_cnt &&
sl->state.callback_unroll_depth == cur->callback_unroll_depth) {
verbose_linfo(env, insn_idx, "; ");
verbose(env, "infinite loop detected at insn %d\n", insn_idx);
@@ -19408,7 +19448,10 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
struct bpf_insn insn_buf[16];
struct bpf_prog *new_prog;
struct bpf_map *map_ptr;
- int i, ret, cnt, delta = 0;
+ int i, ret, cnt, delta = 0, cur_subprog = 0;
+ struct bpf_subprog_info *subprogs = env->subprog_info;
+ u16 stack_depth = subprogs[cur_subprog].stack_depth;
+ u16 stack_depth_extra = 0;
if (env->seen_exception && !env->exception_callback_subprog) {
struct bpf_insn patch[] = {
@@ -19428,7 +19471,7 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
mark_subprog_exc_cb(env, env->exception_callback_subprog);
}
- for (i = 0; i < insn_cnt; i++, insn++) {
+ for (i = 0; i < insn_cnt;) {
/* Make divide-by-zero exceptions impossible. */
if (insn->code == (BPF_ALU64 | BPF_MOD | BPF_X) ||
insn->code == (BPF_ALU64 | BPF_DIV | BPF_X) ||
@@ -19467,7 +19510,7 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
delta += cnt - 1;
env->prog = prog = new_prog;
insn = new_prog->insnsi + i + delta;
- continue;
+ goto next_insn;
}
/* Implement LD_ABS and LD_IND with a rewrite, if supported by the program type. */
@@ -19487,7 +19530,7 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
delta += cnt - 1;
env->prog = prog = new_prog;
insn = new_prog->insnsi + i + delta;
- continue;
+ goto next_insn;
}
/* Rewrite pointer arithmetic to mitigate speculation attacks. */
@@ -19502,7 +19545,7 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
aux = &env->insn_aux_data[i + delta];
if (!aux->alu_state ||
aux->alu_state == BPF_ALU_NON_POINTER)
- continue;
+ goto next_insn;
isneg = aux->alu_state & BPF_ALU_NEG_VALUE;
issrc = (aux->alu_state & BPF_ALU_SANITIZE) ==
@@ -19540,19 +19583,39 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
delta += cnt - 1;
env->prog = prog = new_prog;
insn = new_prog->insnsi + i + delta;
- continue;
+ goto next_insn;
+ }
+
+ if (insn->code == (BPF_JMP | BPF_JMA)) {
+ int stack_off = -stack_depth - 8;
+
+ stack_depth_extra = 8;
+ insn_buf[0] = BPF_LDX_MEM(BPF_DW, BPF_REG_AX, BPF_REG_10, stack_off);
+ insn_buf[1] = BPF_JMP_IMM(BPF_JEQ, BPF_REG_AX, 0, insn->off + 2);
+ insn_buf[2] = BPF_ALU64_IMM(BPF_SUB, BPF_REG_AX, 1);
+ insn_buf[3] = BPF_STX_MEM(BPF_DW, BPF_REG_10, BPF_REG_AX, stack_off);
+ cnt = 4;
+
+ new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, cnt);
+ if (!new_prog)
+ return -ENOMEM;
+
+ delta += cnt - 1;
+ env->prog = prog = new_prog;
+ insn = new_prog->insnsi + i + delta;
+ goto next_insn;
}
if (insn->code != (BPF_JMP | BPF_CALL))
- continue;
+ goto next_insn;
if (insn->src_reg == BPF_PSEUDO_CALL)
- continue;
+ goto next_insn;
if (insn->src_reg == BPF_PSEUDO_KFUNC_CALL) {
ret = fixup_kfunc_call(env, insn, insn_buf, i + delta, &cnt);
if (ret)
return ret;
if (cnt == 0)
- continue;
+ goto next_insn;
new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, cnt);
if (!new_prog)
@@ -19561,7 +19624,7 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
delta += cnt - 1;
env->prog = prog = new_prog;
insn = new_prog->insnsi + i + delta;
- continue;
+ goto next_insn;
}
if (insn->imm == BPF_FUNC_get_route_realm)
@@ -19609,11 +19672,11 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
}
insn->imm = ret + 1;
- continue;
+ goto next_insn;
}
if (!bpf_map_ptr_unpriv(aux))
- continue;
+ goto next_insn;
/* instead of changing every JIT dealing with tail_call
* emit two extra insns:
@@ -19642,7 +19705,7 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
delta += cnt - 1;
env->prog = prog = new_prog;
insn = new_prog->insnsi + i + delta;
- continue;
+ goto next_insn;
}
if (insn->imm == BPF_FUNC_timer_set_callback) {
@@ -19754,7 +19817,7 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
delta += cnt - 1;
env->prog = prog = new_prog;
insn = new_prog->insnsi + i + delta;
- continue;
+ goto next_insn;
}
BUILD_BUG_ON(!__same_type(ops->map_lookup_elem,
@@ -19785,31 +19848,31 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
switch (insn->imm) {
case BPF_FUNC_map_lookup_elem:
insn->imm = BPF_CALL_IMM(ops->map_lookup_elem);
- continue;
+ goto next_insn;
case BPF_FUNC_map_update_elem:
insn->imm = BPF_CALL_IMM(ops->map_update_elem);
- continue;
+ goto next_insn;
case BPF_FUNC_map_delete_elem:
insn->imm = BPF_CALL_IMM(ops->map_delete_elem);
- continue;
+ goto next_insn;
case BPF_FUNC_map_push_elem:
insn->imm = BPF_CALL_IMM(ops->map_push_elem);
- continue;
+ goto next_insn;
case BPF_FUNC_map_pop_elem:
insn->imm = BPF_CALL_IMM(ops->map_pop_elem);
- continue;
+ goto next_insn;
case BPF_FUNC_map_peek_elem:
insn->imm = BPF_CALL_IMM(ops->map_peek_elem);
- continue;
+ goto next_insn;
case BPF_FUNC_redirect_map:
insn->imm = BPF_CALL_IMM(ops->map_redirect);
- continue;
+ goto next_insn;
case BPF_FUNC_for_each_map_elem:
insn->imm = BPF_CALL_IMM(ops->map_for_each_callback);
- continue;
+ goto next_insn;
case BPF_FUNC_map_lookup_percpu_elem:
insn->imm = BPF_CALL_IMM(ops->map_lookup_percpu_elem);
- continue;
+ goto next_insn;
}
goto patch_call_imm;
@@ -19837,7 +19900,7 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
delta += cnt - 1;
env->prog = prog = new_prog;
insn = new_prog->insnsi + i + delta;
- continue;
+ goto next_insn;
}
/* Implement bpf_get_func_arg inline. */
@@ -19862,7 +19925,7 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
delta += cnt - 1;
env->prog = prog = new_prog;
insn = new_prog->insnsi + i + delta;
- continue;
+ goto next_insn;
}
/* Implement bpf_get_func_ret inline. */
@@ -19890,7 +19953,7 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
delta += cnt - 1;
env->prog = prog = new_prog;
insn = new_prog->insnsi + i + delta;
- continue;
+ goto next_insn;
}
/* Implement get_func_arg_cnt inline. */
@@ -19905,7 +19968,7 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
env->prog = prog = new_prog;
insn = new_prog->insnsi + i + delta;
- continue;
+ goto next_insn;
}
/* Implement bpf_get_func_ip inline. */
@@ -19920,7 +19983,7 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
env->prog = prog = new_prog;
insn = new_prog->insnsi + i + delta;
- continue;
+ goto next_insn;
}
/* Implement bpf_kptr_xchg inline */
@@ -19938,7 +20001,7 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
delta += cnt - 1;
env->prog = prog = new_prog;
insn = new_prog->insnsi + i + delta;
- continue;
+ goto next_insn;
}
patch_call_imm:
fn = env->ops->get_func_proto(insn->imm, env->prog);
@@ -19952,6 +20015,39 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
return -EFAULT;
}
insn->imm = fn->func - __bpf_call_base;
+next_insn:
+ if (subprogs[cur_subprog + 1].start == i + delta + 1) {
+ subprogs[cur_subprog].stack_depth += stack_depth_extra;
+ subprogs[cur_subprog].stack_extra = stack_depth_extra;
+ cur_subprog++;
+ stack_depth = subprogs[cur_subprog].stack_depth;
+ stack_depth_extra = 0;
+ }
+ i++; insn++;
+ }
+
+ env->prog->aux->stack_depth = subprogs[0].stack_depth;
+ for (i = 0; i < env->subprog_cnt; i++) {
+ int subprog_start = subprogs[i].start, j;
+ int stack_slots = subprogs[i].stack_extra / 8;
+
+ if (stack_slots >= ARRAY_SIZE(insn_buf)) {
+ verbose(env, "verifier bug: stack_extra is too large\n");
+ return -EFAULT;
+ }
+
+ /* Add insns to subprog prologue to init extra stack */
+ for (j = 0; j < stack_slots; j++)
+ insn_buf[j] = BPF_ST_MEM(BPF_DW, BPF_REG_FP,
+ -subprogs[i].stack_depth + j * 8, BPF_MAX_LOOPS);
+ if (j) {
+ insn_buf[j] = env->prog->insnsi[subprog_start];
+
+ new_prog = bpf_patch_insn_data(env, subprog_start, insn_buf, j + 1);
+ if (!new_prog)
+ return -ENOMEM;
+ env->prog = prog = new_prog;
+ }
}
/* Since poke tab is now finalized, publish aux to tracker. */
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index a241f407c234..932ffef0dc88 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -42,6 +42,7 @@
#define BPF_JSGE 0x70 /* SGE is signed '>=', GE in x86 */
#define BPF_JSLT 0xc0 /* SLT is signed, '<' */
#define BPF_JSLE 0xd0 /* SLE is signed, '<=' */
+#define BPF_JMA 0xe0 /* may_goto */
#define BPF_CALL 0x80 /* function call */
#define BPF_EXIT 0x90 /* function return */
--
2.43.0
