bpf: Recognize addr_space_cast instruction in the verifier.

rY = addr_space_cast(rX, 0, 1) tells the verifier that rY->type = PTR_TO_ARENA.
Any further operations on PTR_TO_ARENA register have to be in 32-bit domain.

The verifier will mark load/store through PTR_TO_ARENA with PROBE_MEM32.
JIT will generate them as kern_vm_start + 32bit_addr memory accesses.

rY = addr_space_cast(rX, 1, 0) tells the verifier that rY->type = unknown scalar.
If arena->map_flags has BPF_F_NO_USER_CONV set then convert cast_user to mov32 as well.
Otherwise JIT will convert it to:
  rY = (u32)rX;
  if (rY)
     rY |= arena->user_vm_start & ~(u64)~0U;
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240308010812.89848-6-alexei.starovoitov@gmail.com

include/linux/bpf.h

@@ -883,6 +883,7 @@ enum bpf_reg_type {
 	 * an explicit null check is required for this struct.
 	 */
 	PTR_TO_MEM,		 /* reg points to valid memory region */
+	PTR_TO_ARENA,
 	PTR_TO_BUF,		 /* reg points to a read/write buffer */
 	PTR_TO_FUNC,		 /* reg points to a bpf program function */
 	CONST_PTR_TO_DYNPTR,	 /* reg points to a const struct bpf_dynptr */

include/linux/bpf_verifier.h

@@ -548,6 +548,7 @@ struct bpf_insn_aux_data {
 	u32 seen; /* this insn was processed by the verifier at env->pass_cnt */
 	bool sanitize_stack_spill; /* subject to Spectre v4 sanitation */
 	bool zext_dst; /* this insn zero extends dst reg */
+	bool needs_zext; /* alu op needs to clear upper bits */
 	bool storage_get_func_atomic; /* bpf_*_storage_get() with atomic memory alloc */
 	bool is_iter_next; /* bpf_iter_<type>_next() kfunc call */
 	bool call_with_percpu_alloc_ptr; /* {this,per}_cpu_ptr() with prog percpu alloc */

kernel/bpf/log.c

@@ -458,6 +458,7 @@ const char *reg_type_str(struct bpf_verifier_env *env, enum bpf_reg_type type)
 		[PTR_TO_XDP_SOCK]	= "xdp_sock",
 		[PTR_TO_BTF_ID]		= "ptr_",
 		[PTR_TO_MEM]		= "mem",
+		[PTR_TO_ARENA]		= "arena",
 		[PTR_TO_BUF]		= "buf",
 		[PTR_TO_FUNC]		= "func",
 		[PTR_TO_MAP_KEY]	= "map_key",
@@ -693,6 +694,8 @@ static void print_reg_state(struct bpf_verifier_env *env,
 	}
 
 	verbose(env, "%s", reg_type_str(env, t));
+	if (t == PTR_TO_ARENA)
+		return;
 	if (t == PTR_TO_STACK) {
 		if (state->frameno != reg->frameno)
 			verbose(env, "[%d]", reg->frameno);

kernel/bpf/syscall.c

@@ -4453,6 +4453,12 @@ static struct bpf_insn *bpf_insn_prepare_dump(const struct bpf_prog *prog,
 			continue;
 		}
 
+		if ((BPF_CLASS(code) == BPF_LDX || BPF_CLASS(code) == BPF_STX ||
+		     BPF_CLASS(code) == BPF_ST) && BPF_MODE(code) == BPF_PROBE_MEM32) {
+			insns[i].code = BPF_CLASS(code) | BPF_SIZE(code) | BPF_MEM;
+			continue;
+		}
+
 		if (code != (BPF_LD | BPF_IMM | BPF_DW))
 			continue;
 

kernel/bpf/verifier.c

@@ -4386,6 +4386,7 @@ static bool is_spillable_regtype(enum bpf_reg_type type)
 	case PTR_TO_MEM:
 	case PTR_TO_FUNC:
 	case PTR_TO_MAP_KEY:
+	case PTR_TO_ARENA:
 		return true;
 	default:
 		return false;
@@ -5828,6 +5829,8 @@ static int check_ptr_alignment(struct bpf_verifier_env *env,
 	case PTR_TO_XDP_SOCK:
 		pointer_desc = "xdp_sock ";
 		break;
+	case PTR_TO_ARENA:
+		return 0;
 	default:
 		break;
 	}
@@ -6937,6 +6940,9 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
 
 		if (!err && value_regno >= 0 && (rdonly_mem || t == BPF_READ))
 			mark_reg_unknown(env, regs, value_regno);
+	} else if (reg->type == PTR_TO_ARENA) {
+		if (t == BPF_READ && value_regno >= 0)
+			mark_reg_unknown(env, regs, value_regno);
 	} else {
 		verbose(env, "R%d invalid mem access '%s'\n", regno,
 			reg_type_str(env, reg->type));
@@ -8408,6 +8414,7 @@ static int check_func_arg_reg_off(struct bpf_verifier_env *env,
 	case PTR_TO_MEM | MEM_RINGBUF:
 	case PTR_TO_BUF:
 	case PTR_TO_BUF | MEM_RDONLY:
+	case PTR_TO_ARENA:
 	case SCALAR_VALUE:
 		return 0;
 	/* All the rest must be rejected, except PTR_TO_BTF_ID which allows
@@ -13852,6 +13859,21 @@ static int adjust_reg_min_max_vals(struct bpf_verifier_env *env,
 
 	dst_reg = &regs[insn->dst_reg];
 	src_reg = NULL;
+
+	if (dst_reg->type == PTR_TO_ARENA) {
+		struct bpf_insn_aux_data *aux = cur_aux(env);
+
+		if (BPF_CLASS(insn->code) == BPF_ALU64)
+			/*
+			 * 32-bit operations zero upper bits automatically.
+			 * 64-bit operations need to be converted to 32.
+			 */
+			aux->needs_zext = true;
+
+		/* Any arithmetic operations are allowed on arena pointers */
+		return 0;
+	}
+
 	if (dst_reg->type != SCALAR_VALUE)
 		ptr_reg = dst_reg;
 	else
@@ -13969,19 +13991,20 @@ static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn)
 	} else if (opcode == BPF_MOV) {
 
 		if (BPF_SRC(insn->code) == BPF_X) {
-			if (insn->imm != 0) {
+			if (BPF_CLASS(insn->code) == BPF_ALU) {
+				if ((insn->off != 0 && insn->off != 8 && insn->off != 16) ||
+				    insn->imm) {
 					verbose(env, "BPF_MOV uses reserved fields\n");
 					return -EINVAL;
 				}
-
-			if (BPF_CLASS(insn->code) == BPF_ALU) {
-				if (insn->off != 0 && insn->off != 8 && insn->off != 16) {
-					verbose(env, "BPF_MOV uses reserved fields\n");
+			} else if (insn->off == BPF_ADDR_SPACE_CAST) {
+				if (insn->imm != 1 && insn->imm != 1u << 16) {
+					verbose(env, "addr_space_cast insn can only convert between address space 1 and 0\n");
 					return -EINVAL;
 				}
 			} else {
-				if (insn->off != 0 && insn->off != 8 && insn->off != 16 &&
-				    insn->off != 32) {
+				if ((insn->off != 0 && insn->off != 8 && insn->off != 16 &&
+				     insn->off != 32) || insn->imm) {
 					verbose(env, "BPF_MOV uses reserved fields\n");
 					return -EINVAL;
 				}
@@ -14008,7 +14031,12 @@ static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn)
 			struct bpf_reg_state *dst_reg = regs + insn->dst_reg;
 
 			if (BPF_CLASS(insn->code) == BPF_ALU64) {
-				if (insn->off == 0) {
+				if (insn->imm) {
+					/* off == BPF_ADDR_SPACE_CAST */
+					mark_reg_unknown(env, regs, insn->dst_reg);
+					if (insn->imm == 1) /* cast from as(1) to as(0) */
+						dst_reg->type = PTR_TO_ARENA;
+				} else if (insn->off == 0) {
 					/* case: R1 = R2
 					 * copy register state to dest reg
 					 */
@@ -15182,6 +15210,10 @@ static int check_ld_imm(struct bpf_verifier_env *env, struct bpf_insn *insn)
 
 	if (insn->src_reg == BPF_PSEUDO_MAP_VALUE ||
 	    insn->src_reg == BPF_PSEUDO_MAP_IDX_VALUE) {
+		if (map->map_type == BPF_MAP_TYPE_ARENA) {
+			__mark_reg_unknown(env, dst_reg);
+			return 0;
+		}
 		dst_reg->type = PTR_TO_MAP_VALUE;
 		dst_reg->off = aux->map_off;
 		WARN_ON_ONCE(map->max_entries != 1);
@@ -16568,6 +16600,8 @@ static bool regsafe(struct bpf_verifier_env *env, struct bpf_reg_state *rold,
 		 * the same stack frame, since fp-8 in foo != fp-8 in bar
 		 */
 		return regs_exact(rold, rcur, idmap) && rold->frameno == rcur->frameno;
+	case PTR_TO_ARENA:
+		return true;
 	default:
 		return regs_exact(rold, rcur, idmap);
 	}
@@ -17443,6 +17477,7 @@ static bool reg_type_mismatch_ok(enum bpf_reg_type type)
 	case PTR_TO_TCP_SOCK:
 	case PTR_TO_XDP_SOCK:
 	case PTR_TO_BTF_ID:
+	case PTR_TO_ARENA:
 		return false;
 	default:
 		return true;
@@ -18296,6 +18331,31 @@ static int resolve_pseudo_ldimm64(struct bpf_verifier_env *env)
 				fdput(f);
 				return -EBUSY;
 			}
+			if (map->map_type == BPF_MAP_TYPE_ARENA) {
+				if (env->prog->aux->arena) {
+					verbose(env, "Only one arena per program\n");
+					fdput(f);
+					return -EBUSY;
+				}
+				if (!env->allow_ptr_leaks || !env->bpf_capable) {
+					verbose(env, "CAP_BPF and CAP_PERFMON are required to use arena\n");
+					fdput(f);
+					return -EPERM;
+				}
+				if (!env->prog->jit_requested) {
+					verbose(env, "JIT is required to use arena\n");
+					return -EOPNOTSUPP;
+				}
+				if (!bpf_jit_supports_arena()) {
+					verbose(env, "JIT doesn't support arena\n");
+					return -EOPNOTSUPP;
+				}
+				env->prog->aux->arena = (void *)map;
+				if (!bpf_arena_get_user_vm_start(env->prog->aux->arena)) {
+					verbose(env, "arena's user address must be set via map_extra or mmap()\n");
+					return -EINVAL;
+				}
+			}
 
 			fdput(f);
 next_insn:
@@ -18917,6 +18977,14 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
 				env->prog->aux->num_exentries++;
 			}
 			continue;
+		case PTR_TO_ARENA:
+			if (BPF_MODE(insn->code) == BPF_MEMSX) {
+				verbose(env, "sign extending loads from arena are not supported yet\n");
+				return -EOPNOTSUPP;
+			}
+			insn->code = BPF_CLASS(insn->code) | BPF_PROBE_MEM32 | BPF_SIZE(insn->code);
+			env->prog->aux->num_exentries++;
+			continue;
 		default:
 			continue;
 		}
@@ -19102,13 +19170,19 @@ static int jit_subprogs(struct bpf_verifier_env *env)
 		func[i]->aux->nr_linfo = prog->aux->nr_linfo;
 		func[i]->aux->jited_linfo = prog->aux->jited_linfo;
 		func[i]->aux->linfo_idx = env->subprog_info[i].linfo_idx;
+		func[i]->aux->arena = prog->aux->arena;
 		num_exentries = 0;
 		insn = func[i]->insnsi;
 		for (j = 0; j < func[i]->len; j++, insn++) {
 			if (BPF_CLASS(insn->code) == BPF_LDX &&
 			    (BPF_MODE(insn->code) == BPF_PROBE_MEM ||
+			     BPF_MODE(insn->code) == BPF_PROBE_MEM32 ||
 			     BPF_MODE(insn->code) == BPF_PROBE_MEMSX))
 				num_exentries++;
+			if ((BPF_CLASS(insn->code) == BPF_STX ||
+			     BPF_CLASS(insn->code) == BPF_ST) &&
+			     BPF_MODE(insn->code) == BPF_PROBE_MEM32)
+				num_exentries++;
 		}
 		func[i]->aux->num_exentries = num_exentries;
 		func[i]->aux->tail_call_reachable = env->subprog_info[i].tail_call_reachable;
@@ -19507,6 +19581,21 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
 	}
 
 	for (i = 0; i < insn_cnt;) {
+		if (insn->code == (BPF_ALU64 | BPF_MOV | BPF_X) && insn->imm) {
+			if ((insn->off == BPF_ADDR_SPACE_CAST && insn->imm == 1) ||
+			    (((struct bpf_map *)env->prog->aux->arena)->map_flags & BPF_F_NO_USER_CONV)) {
+				/* convert to 32-bit mov that clears upper 32-bit */
+				insn->code = BPF_ALU | BPF_MOV | BPF_X;
+				/* clear off, so it's a normal 'wX = wY' from JIT pov */
+				insn->off = 0;
+			} /* cast from as(0) to as(1) should be handled by JIT */
+			goto next_insn;
+		}
+
+		if (env->insn_aux_data[i + delta].needs_zext)
+			/* Convert BPF_CLASS(insn->code) == BPF_ALU64 to 32-bit ALU */
+			insn->code = BPF_ALU | BPF_OP(insn->code) | BPF_SRC(insn->code);
+
 		/* Make divide-by-zero exceptions impossible. */
 		if (insn->code == (BPF_ALU64 | BPF_MOD | BPF_X) ||
 		    insn->code == (BPF_ALU64 | BPF_DIV | BPF_X) ||