nfp: bpf: add helper for validating stack pointers

Our implementation has restriction on stack pointers for function
calls.  Move the common checks into a helper for reuse.  The state
has to be encapsulated into a structure to support parameters
other than BPF_REG_2.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Reviewed-by: Jiong Wang <jiong.wang@netronome.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

drivers/net/ethernet/netronome/nfp/bpf/jit.c

@@ -1366,8 +1366,8 @@ map_call_stack_common(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta)
 
 	/* We only have to reload LM0 if the key is not at start of stack */
 	lm_off = nfp_prog->stack_depth;
-	lm_off += meta->arg2.var_off.value + meta->arg2.off;
-	load_lm_ptr = meta->arg2_var_off || lm_off;
+	lm_off += meta->arg2.reg.var_off.value + meta->arg2.reg.off;
+	load_lm_ptr = meta->arg2.var_off || lm_off;
 
 	/* Set LM0 to start of key */
 	if (load_lm_ptr)

drivers/net/ethernet/netronome/nfp/bpf/main.h

@@ -190,6 +190,16 @@ typedef int (*instr_cb_t)(struct nfp_prog *, struct nfp_insn_meta *);
 #define nfp_meta_next(meta)	list_next_entry(meta, l)
 #define nfp_meta_prev(meta)	list_prev_entry(meta, l)
 
+/**
+ * struct nfp_bpf_reg_state - register state for calls
+ * @reg: BPF register state from latest path
+ * @var_off: for stack arg - changes stack offset on different paths
+ */
+struct nfp_bpf_reg_state {
+	struct bpf_reg_state reg;
+	bool var_off;
+};
+
 #define FLAG_INSN_IS_JUMP_DST	BIT(0)
 
 /**
@@ -207,7 +217,6 @@ typedef int (*instr_cb_t)(struct nfp_prog *, struct nfp_insn_meta *);
  * @func_id: function id for call instructions
  * @arg1: arg1 for call instructions
  * @arg2: arg2 for call instructions
- * @arg2_var_off: arg2 changes stack offset on different paths
  * @off: index of first generated machine instruction (in nfp_prog.prog)
  * @n: eBPF instruction number
  * @flags: eBPF instruction extra optimization flags
@@ -233,8 +242,7 @@ struct nfp_insn_meta {
 		struct {
 			u32 func_id;
 			struct bpf_reg_state arg1;
-			struct bpf_reg_state arg2;
-			bool arg2_var_off;
+			struct nfp_bpf_reg_state arg2;
 		};
 	};
 	unsigned int off;

drivers/net/ethernet/netronome/nfp/bpf/verifier.c

@@ -97,7 +97,7 @@ nfp_record_adjust_head(struct nfp_app_bpf *bpf, struct nfp_prog *nfp_prog,
 		if (nfp_prog->adjust_head_location != meta->n)
 			goto exit_set_location;
 
-		if (meta->arg2.var_off.value != imm)
+		if (meta->arg2.reg.var_off.value != imm)
 			goto exit_set_location;
 	}
 
@@ -106,6 +106,39 @@ exit_set_location:
 	nfp_prog->adjust_head_location = location;
 }
 
+static int
+nfp_bpf_stack_arg_ok(const char *fname, struct bpf_verifier_env *env,
+		     const struct bpf_reg_state *reg,
+		     struct nfp_bpf_reg_state *old_arg)
+{
+	s64 off, old_off;
+
+	if (reg->type != PTR_TO_STACK) {
+		pr_vlog(env, "%s: unsupported ptr type %d\n",
+			fname, reg->type);
+		return false;
+	}
+	if (!tnum_is_const(reg->var_off)) {
+		pr_vlog(env, "%s: variable pointer\n", fname);
+		return false;
+	}
+
+	off = reg->var_off.value + reg->off;
+	if (-off % 4) {
+		pr_vlog(env, "%s: unaligned stack pointer %lld\n", fname, -off);
+		return false;
+	}
+
+	/* Rest of the checks is only if we re-parse the same insn */
+	if (!old_arg)
+		return true;
+
+	old_off = old_arg->reg.var_off.value + old_arg->reg.off;
+	old_arg->var_off |= off != old_off;
+
+	return true;
+}
+
 static int
 nfp_bpf_check_call(struct nfp_prog *nfp_prog, struct bpf_verifier_env *env,
 		   struct nfp_insn_meta *meta)
@@ -114,7 +147,6 @@ nfp_bpf_check_call(struct nfp_prog *nfp_prog, struct bpf_verifier_env *env,
 	const struct bpf_reg_state *reg2 = cur_regs(env) + BPF_REG_2;
 	struct nfp_app_bpf *bpf = nfp_prog->bpf;
 	u32 func_id = meta->insn.imm;
-	s64 off, old_off;
 
 	switch (func_id) {
 	case BPF_FUNC_xdp_adjust_head:
@@ -135,32 +167,15 @@ nfp_bpf_check_call(struct nfp_prog *nfp_prog, struct bpf_verifier_env *env,
 			pr_vlog(env, "map_lookup: not supported by FW\n");
 			return -EOPNOTSUPP;
 		}
-		if (reg2->type != PTR_TO_STACK) {
-			pr_vlog(env,
-				"map_lookup: unsupported key ptr type %d\n",
-				reg2->type);
-			return -EOPNOTSUPP;
-		}
-		if (!tnum_is_const(reg2->var_off)) {
-			pr_vlog(env, "map_lookup: variable key pointer\n");
-			return -EOPNOTSUPP;
-		}
 
-		off = reg2->var_off.value + reg2->off;
-		if (-off % 4) {
-			pr_vlog(env,
-				"map_lookup: unaligned stack pointer %lld\n",
-				-off);
+		if (!nfp_bpf_stack_arg_ok("map_lookup", env, reg2,
+					  meta->func_id ? &meta->arg2 : NULL))
 			return -EOPNOTSUPP;
-		}
 
 		/* Rest of the checks is only if we re-parse the same insn */
 		if (!meta->func_id)
 			break;
 
-		old_off = meta->arg2.var_off.value + meta->arg2.off;
-		meta->arg2_var_off |= off != old_off;
-
 		if (meta->arg1.map_ptr != reg1->map_ptr) {
 			pr_vlog(env, "map_lookup: called for different map\n");
 			return -EOPNOTSUPP;
@@ -173,7 +188,7 @@ nfp_bpf_check_call(struct nfp_prog *nfp_prog, struct bpf_verifier_env *env,
 
 	meta->func_id = func_id;
 	meta->arg1 = *reg1;
-	meta->arg2 = *reg2;
+	meta->arg2.reg = *reg2;
 
 	return 0;
 }