bpf: WARN_ONCE on verifier bugs

Throughout the verifier's logic, there are multiple checks for
inconsistent states that should never happen and would indicate a
verifier bug. These bugs are typically logged in the verifier logs and
sometimes preceded by a WARN_ONCE.

This patch reworks these checks to consistently emit a verifier log AND
a warning when CONFIG_DEBUG_KERNEL is enabled. The consistent use of
WARN_ONCE should help fuzzers (ex. syzkaller) expose any situation
where they are actually able to reach one of those buggy verifier
states.

Acked-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
Link: https://lore.kernel.org/r/aCs1nYvNNMq8dAWP@mail.gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 83c56f4..5b25d27 100644 (file)
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -346,6 +346,12 @@ static inline const char *btf_field_type_name(enum btf_field_type type)
        }
 }
 
+#if IS_ENABLED(CONFIG_DEBUG_KERNEL)
+#define BPF_WARN_ONCE(cond, format...) WARN_ONCE(cond, format)
+#else
+#define BPF_WARN_ONCE(cond, format...) BUILD_BUG_ON_INVALID(cond)
+#endif
+
 static inline u32 btf_field_type_size(enum btf_field_type type)
 {
        switch (type) {

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index cedd668..78c97e1 100644 (file)
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -839,6 +839,17 @@ __printf(3, 4) void verbose_linfo(struct bpf_verifier_env *env,
                                  u32 insn_off,
                                  const char *prefix_fmt, ...);
 
+#define verifier_bug_if(cond, env, fmt, args...)                                               \
+       ({                                                                                      \
+               bool __cond = (cond);                                                           \
+               if (unlikely(__cond)) {                                                         \
+                       BPF_WARN_ONCE(1, "verifier bug: " fmt "(" #cond ")\n", ##args);         \
+                       bpf_log(&env->log, "verifier bug: " fmt "(" #cond ")\n", ##args);       \
+               }                                                                               \
+               (__cond);                                                                       \
+       })
+#define verifier_bug(env, fmt, args...) verifier_bug_if(1, env, fmt, ##args)
+
 static inline struct bpf_func_state *cur_func(struct bpf_verifier_env *env)
 {
        struct bpf_verifier_state *cur = env->cur_state;

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 6b21ca6..0f78283 100644 (file)
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -7659,7 +7659,7 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog)
                return 0;
 
        if (!prog->aux->func_info) {
-               bpf_log(log, "Verifier bug\n");
+               verifier_bug(env, "func_info undefined");
                return -EFAULT;
        }
 
@@ -7683,7 +7683,7 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog)
        tname = btf_name_by_offset(btf, fn_t->name_off);
 
        if (prog->aux->func_info_aux[subprog].unreliable) {
-               bpf_log(log, "Verifier bug in function %s()\n", tname);
+               verifier_bug(env, "unreliable BTF for function %s()", tname);
                return -EFAULT;
        }
        if (prog_type == BPF_PROG_TYPE_EXT)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index f6d3655..d5807d2 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1924,11 +1924,8 @@ static struct bpf_verifier_state *get_loop_entry(struct bpf_verifier_env *env,
        u32 steps = 0;
 
        while (topmost && topmost->loop_entry) {
-               if (steps++ > st->dfs_depth) {
-                       WARN_ONCE(true, "verifier bug: infinite loop in get_loop_entry\n");
-                       verbose(env, "verifier bug: infinite loop in get_loop_entry()\n");
+               if (verifier_bug_if(steps++ > st->dfs_depth, env, "infinite loop"))
                        return ERR_PTR(-EFAULT);
-               }
                topmost = topmost->loop_entry;
        }
        return topmost;
@@ -3460,12 +3457,11 @@ static int mark_reg_read(struct bpf_verifier_env *env,
                /* if read wasn't screened by an earlier write ... */
                if (writes && state->live & REG_LIVE_WRITTEN)
                        break;
-               if (parent->live & REG_LIVE_DONE) {
-                       verbose(env, "verifier BUG type %s var_off %lld off %d\n",
-                               reg_type_str(env, parent->type),
-                               parent->var_off.value, parent->off);
+               if (verifier_bug_if(parent->live & REG_LIVE_DONE, env,
+                                   "type %s var_off %lld off %d",
+                                   reg_type_str(env, parent->type),
+                                   parent->var_off.value, parent->off))
                        return -EFAULT;
-               }
                /* The first condition is more likely to be true than the
                 * second, checked it first.
                 */
@@ -3858,14 +3854,14 @@ static int push_insn_history(struct bpf_verifier_env *env, struct bpf_verifier_s
                /* atomic instructions push insn_flags twice, for READ and
                 * WRITE sides, but they should agree on stack slot
                 */
-               WARN_ONCE((env->cur_hist_ent->flags & insn_flags) &&
-                         (env->cur_hist_ent->flags & insn_flags) != insn_flags,
-                         "verifier insn history bug: insn_idx %d cur flags %x new flags %x\n",
-                         env->insn_idx, env->cur_hist_ent->flags, insn_flags);
+               verifier_bug_if((env->cur_hist_ent->flags & insn_flags) &&
+                               (env->cur_hist_ent->flags & insn_flags) != insn_flags,
+                               env, "insn history: insn_idx %d cur flags %x new flags %x",
+                               env->insn_idx, env->cur_hist_ent->flags, insn_flags);
                env->cur_hist_ent->flags |= insn_flags;
-               WARN_ONCE(env->cur_hist_ent->linked_regs != 0,
-                         "verifier insn history bug: insn_idx %d linked_regs != 0: %#llx\n",
-                         env->insn_idx, env->cur_hist_ent->linked_regs);
+               verifier_bug_if(env->cur_hist_ent->linked_regs != 0, env,
+                               "insn history: insn_idx %d linked_regs: %#llx",
+                               env->insn_idx, env->cur_hist_ent->linked_regs);
                env->cur_hist_ent->linked_regs = linked_regs;
                return 0;
        }
@@ -3988,8 +3984,7 @@ static inline u32 bt_empty(struct backtrack_state *bt)
 static inline int bt_subprog_enter(struct backtrack_state *bt)
 {
        if (bt->frame == MAX_CALL_FRAMES - 1) {
-               verbose(bt->env, "BUG subprog enter from frame %d\n", bt->frame);
-               WARN_ONCE(1, "verifier backtracking bug");
+               verifier_bug(bt->env, "subprog enter from frame %d", bt->frame);
                return -EFAULT;
        }
        bt->frame++;
@@ -3999,8 +3994,7 @@ static inline int bt_subprog_enter(struct backtrack_state *bt)
 static inline int bt_subprog_exit(struct backtrack_state *bt)
 {
        if (bt->frame == 0) {
-               verbose(bt->env, "BUG subprog exit from frame 0\n");
-               WARN_ONCE(1, "verifier backtracking bug");
+               verifier_bug(bt->env, "subprog exit from frame 0");
                return -EFAULT;
        }
        bt->frame--;
@@ -4278,14 +4272,15 @@ static int backtrack_insn(struct bpf_verifier_env *env, int idx, int subseq_idx,
                                 * should be literally next instruction in
                                 * caller program
                                 */
-                               WARN_ONCE(idx + 1 != subseq_idx, "verifier backtracking bug");
+                               verifier_bug_if(idx + 1 != subseq_idx, env,
+                                               "extra insn from subprog");
                                /* r1-r5 are invalidated after subprog call,
                                 * so for global func call it shouldn't be set
                                 * anymore
                                 */
                                if (bt_reg_mask(bt) & BPF_REGMASK_ARGS) {
-                                       verbose(env, "BUG regs %x\n", bt_reg_mask(bt));
-                                       WARN_ONCE(1, "verifier backtracking bug");
+                                       verifier_bug(env, "global subprog unexpected regs %x",
+                                                    bt_reg_mask(bt));
                                        return -EFAULT;
                                }
                                /* global subprog always sets R0 */
@@ -4299,16 +4294,17 @@ static int backtrack_insn(struct bpf_verifier_env *env, int idx, int subseq_idx,
                                 * the current frame should be zero by now
                                 */
                                if (bt_reg_mask(bt) & ~BPF_REGMASK_ARGS) {
-                                       verbose(env, "BUG regs %x\n", bt_reg_mask(bt));
-                                       WARN_ONCE(1, "verifier backtracking bug");
+                                       verifier_bug(env, "static subprog unexpected regs %x",
+                                                    bt_reg_mask(bt));
                                        return -EFAULT;
                                }
                                /* we are now tracking register spills correctly,
                                 * so any instance of leftover slots is a bug
                                 */
                                if (bt_stack_mask(bt) != 0) {
-                                       verbose(env, "BUG stack slots %llx\n", bt_stack_mask(bt));
-                                       WARN_ONCE(1, "verifier backtracking bug (subprog leftover stack slots)");
+                                       verifier_bug(env,
+                                                    "static subprog leftover stack slots %llx",
+                                                    bt_stack_mask(bt));
                                        return -EFAULT;
                                }
                                /* propagate r1-r5 to the caller */
@@ -4331,13 +4327,13 @@ static int backtrack_insn(struct bpf_verifier_env *env, int idx, int subseq_idx,
                         * not actually arguments passed directly to callback subprogs
                         */
                        if (bt_reg_mask(bt) & ~BPF_REGMASK_ARGS) {
-                               verbose(env, "BUG regs %x\n", bt_reg_mask(bt));
-                               WARN_ONCE(1, "verifier backtracking bug");
+                               verifier_bug(env, "callback unexpected regs %x",
+                                            bt_reg_mask(bt));
                                return -EFAULT;
                        }
                        if (bt_stack_mask(bt) != 0) {
-                               verbose(env, "BUG stack slots %llx\n", bt_stack_mask(bt));
-                               WARN_ONCE(1, "verifier backtracking bug (callback leftover stack slots)");
+                               verifier_bug(env, "callback leftover stack slots %llx",
+                                            bt_stack_mask(bt));
                                return -EFAULT;
                        }
                        /* clear r1-r5 in callback subprog's mask */
@@ -4356,11 +4352,11 @@ static int backtrack_insn(struct bpf_verifier_env *env, int idx, int subseq_idx,
                        /* regular helper call sets R0 */
                        bt_clear_reg(bt, BPF_REG_0);
                        if (bt_reg_mask(bt) & BPF_REGMASK_ARGS) {
-                               /* if backtracing was looking for registers R1-R5
+                               /* if backtracking was looking for registers R1-R5
                                 * they should have been found already.
                                 */
-                               verbose(env, "BUG regs %x\n", bt_reg_mask(bt));
-                               WARN_ONCE(1, "verifier backtracking bug");
+                               verifier_bug(env, "backtracking call unexpected regs %x",
+                                            bt_reg_mask(bt));
                                return -EFAULT;
                        }
                } else if (opcode == BPF_EXIT) {
@@ -4378,8 +4374,8 @@ static int backtrack_insn(struct bpf_verifier_env *env, int idx, int subseq_idx,
                                for (i = BPF_REG_1; i <= BPF_REG_5; i++)
                                        bt_clear_reg(bt, i);
                        if (bt_reg_mask(bt) & BPF_REGMASK_ARGS) {
-                               verbose(env, "BUG regs %x\n", bt_reg_mask(bt));
-                               WARN_ONCE(1, "verifier backtracking bug");
+                               verifier_bug(env, "backtracking exit unexpected regs %x",
+                                            bt_reg_mask(bt));
                                return -EFAULT;
                        }
 
@@ -4720,9 +4716,8 @@ static int __mark_chain_precision(struct bpf_verifier_env *env, int regno)
                                return 0;
                        }
 
-                       verbose(env, "BUG backtracking func entry subprog %d reg_mask %x stack_mask %llx\n",
-                               st->frame[0]->subprogno, bt_reg_mask(bt), bt_stack_mask(bt));
-                       WARN_ONCE(1, "verifier backtracking bug");
+                       verifier_bug(env, "backtracking func entry subprog %d reg_mask %x stack_mask %llx",
+                                    st->frame[0]->subprogno, bt_reg_mask(bt), bt_stack_mask(bt));
                        return -EFAULT;
                }
 
@@ -4758,8 +4753,7 @@ static int __mark_chain_precision(struct bpf_verifier_env *env, int regno)
                                 * It means the backtracking missed the spot where
                                 * particular register was initialized with a constant.
                                 */
-                               verbose(env, "BUG backtracking idx %d\n", i);
-                               WARN_ONCE(1, "verifier backtracking bug");
+                               verifier_bug(env, "backtracking idx %d", i);
                                return -EFAULT;
                        }
                }
@@ -4784,12 +4778,10 @@ static int __mark_chain_precision(struct bpf_verifier_env *env, int regno)
 
                        bitmap_from_u64(mask, bt_frame_stack_mask(bt, fr));
                        for_each_set_bit(i, mask, 64) {
-                               if (i >= func->allocated_stack / BPF_REG_SIZE) {
-                                       verbose(env, "BUG backtracking (stack slot %d, total slots %d)\n",
-                                               i, func->allocated_stack / BPF_REG_SIZE);
-                                       WARN_ONCE(1, "verifier backtracking bug (stack slot out of bounds)");
+                               if (verifier_bug_if(i >= func->allocated_stack / BPF_REG_SIZE,
+                                                   env, "stack slot %d, total slots %d",
+                                                   i, func->allocated_stack / BPF_REG_SIZE))
                                        return -EFAULT;
-                               }
 
                                if (!is_spilled_scalar_reg(&func->stack[i])) {
                                        bt_clear_frame_slot(bt, fr, i);
@@ -6562,21 +6554,18 @@ continue_func:
                /* find the callee */
                next_insn = i + insn[i].imm + 1;
                sidx = find_subprog(env, next_insn);
-               if (sidx < 0) {
-                       WARN_ONCE(1, "verifier bug. No program starts at insn %d\n",
-                                 next_insn);
+               if (verifier_bug_if(sidx < 0, env, "callee not found at insn %d", next_insn))
                        return -EFAULT;
-               }
                if (subprog[sidx].is_async_cb) {
                        if (subprog[sidx].has_tail_call) {
-                               verbose(env, "verifier bug. subprog has tail_call and async cb\n");
+                               verifier_bug(env, "subprog has tail_call and async cb");
                                return -EFAULT;
                        }
                        /* async callbacks don't increase bpf prog stack size unless called directly */
                        if (!bpf_pseudo_call(insn + i))
                                continue;
                        if (subprog[sidx].is_exception_cb) {
-                               verbose(env, "insn %d cannot call exception cb directly\n", i);
+                               verbose(env, "insn %d cannot call exception cb directly", i);
                                return -EINVAL;
                        }
                }
@@ -6676,11 +6665,8 @@ static int get_callee_stack_depth(struct bpf_verifier_env *env,
        int start = idx + insn->imm + 1, subprog;
 
        subprog = find_subprog(env, start);
-       if (subprog < 0) {
-               WARN_ONCE(1, "verifier bug. No program starts at insn %d\n",
-                         start);
+       if (verifier_bug_if(subprog < 0, env, "get stack depth: no program at insn %d", start))
                return -EFAULT;
-       }
        return env->subprog_info[subprog].stack_depth;
 }
 #endif
@@ -7985,7 +7971,7 @@ static int check_stack_range_initialized(
                slot = -i - 1;
                spi = slot / BPF_REG_SIZE;
                if (state->allocated_stack <= slot) {
-                       verbose(env, "verifier bug: allocated_stack too small\n");
+                       verbose(env, "allocated_stack too small\n");
                        return -EFAULT;
                }
 
@@ -8414,7 +8400,7 @@ static int process_timer_func(struct bpf_verifier_env *env, int regno,
                return -EINVAL;
        }
        if (meta->map_ptr) {
-               verbose(env, "verifier bug. Two map pointers in a timer helper\n");
+               verifier_bug(env, "Two map pointers in a timer helper");
                return -EFAULT;
        }
        meta->map_uid = reg->map_uid;
@@ -10286,8 +10272,7 @@ static int setup_func_entry(struct bpf_verifier_env *env, int subprog, int calls
        }
 
        if (state->frame[state->curframe + 1]) {
-               verbose(env, "verifier bug. Frame %d already allocated\n",
-                       state->curframe + 1);
+               verifier_bug(env, "Frame %d already allocated", state->curframe + 1);
                return -EFAULT;
        }
 
@@ -10401,8 +10386,7 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env, int subprog,
                        if (err)
                                return err;
                } else {
-                       bpf_log(log, "verifier bug: unrecognized arg#%d type %d\n",
-                               i, arg->arg_type);
+                       verifier_bug(env, "unrecognized arg#%d type %d", i, arg->arg_type);
                        return -EFAULT;
                }
        }
@@ -10465,13 +10449,13 @@ static int push_callback_call(struct bpf_verifier_env *env, struct bpf_insn *ins
        env->subprog_info[subprog].is_cb = true;
        if (bpf_pseudo_kfunc_call(insn) &&
            !is_callback_calling_kfunc(insn->imm)) {
-               verbose(env, "verifier bug: kfunc %s#%d not marked as callback-calling\n",
-                       func_id_name(insn->imm), insn->imm);
+               verifier_bug(env, "kfunc %s#%d not marked as callback-calling",
+                            func_id_name(insn->imm), insn->imm);
                return -EFAULT;
        } else if (!bpf_pseudo_kfunc_call(insn) &&
                   !is_callback_calling_function(insn->imm)) { /* helper */
-               verbose(env, "verifier bug: helper %s#%d not marked as callback-calling\n",
-                       func_id_name(insn->imm), insn->imm);
+               verifier_bug(env, "helper %s#%d not marked as callback-calling",
+                            func_id_name(insn->imm), insn->imm);
                return -EFAULT;
        }
 
@@ -10523,10 +10507,9 @@ static int check_func_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 
        target_insn = *insn_idx + insn->imm + 1;
        subprog = find_subprog(env, target_insn);
-       if (subprog < 0) {
-               verbose(env, "verifier bug. No program starts at insn %d\n", target_insn);
+       if (verifier_bug_if(subprog < 0, env, "target of func call at insn %d is not a program",
+                           target_insn))
                return -EFAULT;
-       }
 
        caller = state->frame[state->curframe];
        err = btf_check_subprog_call(env, subprog, caller->regs);
@@ -11125,7 +11108,7 @@ static int check_bpf_snprintf_call(struct bpf_verifier_env *env,
        err = fmt_map->ops->map_direct_value_addr(fmt_map, &fmt_addr,
                                                  fmt_map_off);
        if (err) {
-               verbose(env, "verifier bug\n");
+               verbose(env, "failed to retrieve map value address\n");
                return -EFAULT;
        }
        fmt = (char *)(long)fmt_addr + fmt_map_off;
@@ -19706,10 +19689,9 @@ process_bpf_exit:
                                                return err;
                                        break;
                                } else {
-                                       if (WARN_ON_ONCE(env->cur_state->loop_entry)) {
-                                               verbose(env, "verifier bug: env->cur_state->loop_entry != NULL\n");
+                                       if (verifier_bug_if(env->cur_state->loop_entry, env,
+                                                           "broken loop detection"))
                                                return -EFAULT;
-                                       }
                                        do_print_state = true;
                                        continue;
                                }
@@ -20767,10 +20749,9 @@ static int opt_subreg_zext_lo32_rnd_hi32(struct bpf_verifier_env *env,
                if (bpf_pseudo_kfunc_call(&insn))
                        continue;
 
-               if (WARN_ON(load_reg == -1)) {
-                       verbose(env, "verifier bug. zext_dst is set, but no reg is defined\n");
+               if (verifier_bug_if(load_reg == -1, env,
+                                   "zext_dst is set, but no reg is defined"))
                        return -EFAULT;
-               }
 
                zext_patch[0] = insn;
                zext_patch[1].dst_reg = load_reg;
@@ -21087,11 +21068,9 @@ static int jit_subprogs(struct bpf_verifier_env *env)
                 * propagated in any case.
                 */
                subprog = find_subprog(env, i + insn->imm + 1);
-               if (subprog < 0) {
-                       WARN_ONCE(1, "verifier bug. No program starts at insn %d\n",
-                                 i + insn->imm + 1);
+               if (verifier_bug_if(subprog < 0, env, "No program to jit at insn %d",
+                                   i + insn->imm + 1))
                        return -EFAULT;
-               }
                /* temporarily remember subprog id inside insn instead of
                 * aux_data, since next loop will split up all insns into funcs
                 */
@@ -22454,7 +22433,7 @@ next_insn:
                        continue;
                /* We need two slots in case timed may_goto is supported. */
                if (stack_slots > slots) {
-                       verbose(env, "verifier bug: stack_slots supports may_goto only\n");
+                       verifier_bug(env, "stack_slots supports may_goto only");
                        return -EFAULT;
                }