bpf: Introduce MEM_RDONLY flag

This patch introduce a flag MEM_RDONLY to tag a reg value
pointing to read-only memory. It makes the following changes:

1. PTR_TO_RDWR_BUF -> PTR_TO_BUF
2. PTR_TO_RDONLY_BUF -> PTR_TO_BUF | MEM_RDONLY

Signed-off-by: Hao Luo <haoluo@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211217003152.48334-6-haoluo@google.com

3 files changed, 53 insertions, 38 deletions

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 4e2ca7bea6c4..d1447b075c73 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -4944,8 +4944,7 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
 
 		type = base_type(ctx_arg_info->reg_type);
 		flag = type_flag(ctx_arg_info->reg_type);
-		if (ctx_arg_info->offset == off &&
-		    (type == PTR_TO_RDWR_BUF || type == PTR_TO_RDONLY_BUF) &&
+		if (ctx_arg_info->offset == off && type == PTR_TO_BUF &&
 		    (flag & PTR_MAYBE_NULL)) {
 			info->reg_type = ctx_arg_info->reg_type;
 			return true;
diff --git a/kernel/bpf/map_iter.c b/kernel/bpf/map_iter.c
index 631f0e44b7a9..b0fa190b0979 100644
--- a/kernel/bpf/map_iter.c
+++ b/kernel/bpf/map_iter.c
@@ -174,9 +174,9 @@ static const struct bpf_iter_reg bpf_map_elem_reg_info = {
 	.ctx_arg_info_size	= 2,
 	.ctx_arg_info		= {
 		{ offsetof(struct bpf_iter__bpf_map_elem, key),
-		  PTR_TO_RDONLY_BUF | PTR_MAYBE_NULL },
+		  PTR_TO_BUF | PTR_MAYBE_NULL | MEM_RDONLY },
 		{ offsetof(struct bpf_iter__bpf_map_elem, value),
-		  PTR_TO_RDWR_BUF | PTR_MAYBE_NULL },
+		  PTR_TO_BUF | PTR_MAYBE_NULL },
 	},
 };
 
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 97e9d3f31443..e0a8a55ea3df 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -455,6 +455,11 @@ static bool reg_type_may_be_refcounted_or_null(enum bpf_reg_type type)
 		base_type(type) == PTR_TO_MEM;
 }
 
+static bool type_is_rdonly_mem(u32 type)
+{
+	return type & MEM_RDONLY;
+}
+
 static bool arg_type_may_be_refcounted(enum bpf_arg_type type)
 {
 	return type == ARG_PTR_TO_SOCK_COMMON;
@@ -530,7 +535,7 @@ static bool is_cmpxchg_insn(const struct bpf_insn *insn)
 static const char *reg_type_str(struct bpf_verifier_env *env,
 				enum bpf_reg_type type)
 {
-	char postfix[16] = {0};
+	char postfix[16] = {0}, prefix[16] = {0};
 	static const char * const str[] = {
 		[NOT_INIT]		= "?",
 		[SCALAR_VALUE]		= "inv",
@@ -550,8 +555,7 @@ static const char *reg_type_str(struct bpf_verifier_env *env,
 		[PTR_TO_BTF_ID]		= "ptr_",
 		[PTR_TO_PERCPU_BTF_ID]	= "percpu_ptr_",
 		[PTR_TO_MEM]		= "mem",
-		[PTR_TO_RDONLY_BUF]	= "rdonly_buf",
-		[PTR_TO_RDWR_BUF]	= "rdwr_buf",
+		[PTR_TO_BUF]		= "buf",
 		[PTR_TO_FUNC]		= "func",
 		[PTR_TO_MAP_KEY]	= "map_key",
 	};
@@ -564,8 +568,11 @@ static const char *reg_type_str(struct bpf_verifier_env *env,
 			strncpy(postfix, "_or_null", 16);
 	}
 
-	snprintf(env->type_str_buf, TYPE_STR_BUF_LEN, "%s%s",
-		 str[base_type(type)], postfix);
+	if (type & MEM_RDONLY)
+		strncpy(prefix, "rdonly_", 16);
+
+	snprintf(env->type_str_buf, TYPE_STR_BUF_LEN, "%s%s%s",
+		 prefix, str[base_type(type)], postfix);
 	return env->type_str_buf;
 }
 
@@ -2755,8 +2762,7 @@ static bool is_spillable_regtype(enum bpf_reg_type type)
 	case PTR_TO_TCP_SOCK:
 	case PTR_TO_XDP_SOCK:
 	case PTR_TO_BTF_ID:
-	case PTR_TO_RDONLY_BUF:
-	case PTR_TO_RDWR_BUF:
+	case PTR_TO_BUF:
 	case PTR_TO_PERCPU_BTF_ID:
 	case PTR_TO_MEM:
 	case PTR_TO_FUNC:
@@ -4508,22 +4514,28 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
 	} else if (reg->type == CONST_PTR_TO_MAP) {
 		err = check_ptr_to_map_access(env, regs, regno, off, size, t,
 					      value_regno);
-	} else if (reg->type == PTR_TO_RDONLY_BUF) {
-		if (t == BPF_WRITE) {
-			verbose(env, "R%d cannot write into %s\n",
-				regno, reg_type_str(env, reg->type));
-			return -EACCES;
+	} else if (base_type(reg->type) == PTR_TO_BUF) {
+		bool rdonly_mem = type_is_rdonly_mem(reg->type);
+		const char *buf_info;
+		u32 *max_access;
+
+		if (rdonly_mem) {
+			if (t == BPF_WRITE) {
+				verbose(env, "R%d cannot write into %s\n",
+					regno, reg_type_str(env, reg->type));
+				return -EACCES;
+			}
+			buf_info = "rdonly";
+			max_access = &env->prog->aux->max_rdonly_access;
+		} else {
+			buf_info = "rdwr";
+			max_access = &env->prog->aux->max_rdwr_access;
 		}
+
 		err = check_buffer_access(env, reg, regno, off, size, false,
-					  "rdonly",
-					  &env->prog->aux->max_rdonly_access);
-		if (!err && value_regno >= 0)
-			mark_reg_unknown(env, regs, value_regno);
-	} else if (reg->type == PTR_TO_RDWR_BUF) {
-		err = check_buffer_access(env, reg, regno, off, size, false,
-					  "rdwr",
-					  &env->prog->aux->max_rdwr_access);
-		if (!err && t == BPF_READ && value_regno >= 0)
+					  buf_info, max_access);
+
+		if (!err && value_regno >= 0 && (rdonly_mem || t == BPF_READ))
 			mark_reg_unknown(env, regs, value_regno);
 	} else {
 		verbose(env, "R%d invalid mem access '%s'\n", regno,
@@ -4771,8 +4783,10 @@ static int check_helper_mem_access(struct bpf_verifier_env *env, int regno,
 				   struct bpf_call_arg_meta *meta)
 {
 	struct bpf_reg_state *regs = cur_regs(env), *reg = &regs[regno];
+	const char *buf_info;
+	u32 *max_access;
 
-	switch (reg->type) {
+	switch (base_type(reg->type)) {
 	case PTR_TO_PACKET:
 	case PTR_TO_PACKET_META:
 		return check_packet_access(env, regno, reg->off, access_size,
@@ -4791,18 +4805,20 @@ static int check_helper_mem_access(struct bpf_verifier_env *env, int regno,
 		return check_mem_region_access(env, regno, reg->off,
 					       access_size, reg->mem_size,
 					       zero_size_allowed);
-	case PTR_TO_RDONLY_BUF:
-		if (meta && meta->raw_mode)
-			return -EACCES;
-		return check_buffer_access(env, reg, regno, reg->off,
-					   access_size, zero_size_allowed,
-					   "rdonly",
-					   &env->prog->aux->max_rdonly_access);
-	case PTR_TO_RDWR_BUF:
+	case PTR_TO_BUF:
+		if (type_is_rdonly_mem(reg->type)) {
+			if (meta && meta->raw_mode)
+				return -EACCES;
+
+			buf_info = "rdonly";
+			max_access = &env->prog->aux->max_rdonly_access;
+		} else {
+			buf_info = "rdwr";
+			max_access = &env->prog->aux->max_rdwr_access;
+		}
 		return check_buffer_access(env, reg, regno, reg->off,
 					   access_size, zero_size_allowed,
-					   "rdwr",
-					   &env->prog->aux->max_rdwr_access);
+					   buf_info, max_access);
 	case PTR_TO_STACK:
 		return check_stack_range_initialized(
 				env,
@@ -5081,8 +5097,8 @@ static const struct bpf_reg_types mem_types = {
 		PTR_TO_MAP_KEY,
 		PTR_TO_MAP_VALUE,
 		PTR_TO_MEM,
-		PTR_TO_RDONLY_BUF,
-		PTR_TO_RDWR_BUF,
+		PTR_TO_BUF,
+		PTR_TO_BUF | MEM_RDONLY,
 	},
 };