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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Hao Luo <haoluo@google.com>,
        Alexei Starovoitov <ast@kernel.org>
Subject: [PATCH 5.16 006/227] bpf: Introduce MEM_RDONLY flag
Date:   Mon, 21 Feb 2022 09:47:05 +0100
Message-Id: <20220221084935.044999793@linuxfoundation.org>
In-Reply-To: <20220221084934.836145070@linuxfoundation.org>
References: <20220221084934.836145070@linuxfoundation.org>
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From: Hao Luo <haoluo@google.com>

commit 20b2aff4bc15bda809f994761d5719827d66c0b4 upstream.

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
Cc: stable@vger.kernel.org # 5.16.x
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 include/linux/bpf.h       |    8 ++--
 kernel/bpf/btf.c          |    3 -
 kernel/bpf/map_iter.c     |    4 +-
 kernel/bpf/verifier.c     |   84 +++++++++++++++++++++++++++-------------------
 net/core/bpf_sk_storage.c |    2 -
 net/core/sock_map.c       |    2 -
 6 files changed, 60 insertions(+), 43 deletions(-)

--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -311,7 +311,10 @@ enum bpf_type_flag {
 	/* PTR may be NULL. */
 	PTR_MAYBE_NULL		= BIT(0 + BPF_BASE_TYPE_BITS),
 
-	__BPF_TYPE_LAST_FLAG	= PTR_MAYBE_NULL,
+	/* MEM is read-only. */
+	MEM_RDONLY		= BIT(1 + BPF_BASE_TYPE_BITS),
+
+	__BPF_TYPE_LAST_FLAG	= MEM_RDONLY,
 };
 
 /* Max number of base types. */
@@ -492,8 +495,7 @@ enum bpf_reg_type {
 	 * an explicit null check is required for this struct.
 	 */
 	PTR_TO_MEM,		 /* reg points to valid memory region */
-	PTR_TO_RDONLY_BUF,	 /* reg points to a readonly buffer */
-	PTR_TO_RDWR_BUF,	 /* reg points to a read/write buffer */
+	PTR_TO_BUF,		 /* reg points to a read/write buffer */
 	PTR_TO_PERCPU_BTF_ID,	 /* reg points to a percpu kernel variable */
 	PTR_TO_FUNC,		 /* reg points to a bpf program function */
 	__BPF_REG_TYPE_MAX,
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -4932,8 +4932,7 @@ bool btf_ctx_access(int off, int size, e
 
 		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;
--- a/kernel/bpf/map_iter.c
+++ b/kernel/bpf/map_iter.c
@@ -174,9 +174,9 @@ static const struct bpf_iter_reg bpf_map
 	.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 },
 	},
 };
 
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -452,6 +452,11 @@ static bool reg_type_may_be_refcounted_o
 		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;
@@ -527,7 +532,7 @@ static bool is_cmpxchg_insn(const struct
 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",
@@ -547,8 +552,7 @@ static const char *reg_type_str(struct b
 		[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",
 	};
@@ -561,8 +565,11 @@ static const char *reg_type_str(struct b
 			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;
 }
 
@@ -2688,8 +2695,7 @@ static bool is_spillable_regtype(enum bp
 	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:
@@ -4442,22 +4448,28 @@ static int check_mem_access(struct bpf_v
 	} 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,
@@ -4718,8 +4730,10 @@ static int check_helper_mem_access(struc
 				   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,
@@ -4738,18 +4752,20 @@ static int check_helper_mem_access(struc
 		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,
@@ -5028,8 +5044,8 @@ static const struct bpf_reg_types mem_ty
 		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,
 	},
 };
 
--- a/net/core/bpf_sk_storage.c
+++ b/net/core/bpf_sk_storage.c
@@ -929,7 +929,7 @@ static struct bpf_iter_reg bpf_sk_storag
 		{ offsetof(struct bpf_iter__bpf_sk_storage_map, sk),
 		  PTR_TO_BTF_ID_OR_NULL },
 		{ offsetof(struct bpf_iter__bpf_sk_storage_map, value),
-		  PTR_TO_RDWR_BUF | PTR_MAYBE_NULL },
+		  PTR_TO_BUF | PTR_MAYBE_NULL },
 	},
 	.seq_info		= &iter_seq_info,
 };
--- a/net/core/sock_map.c
+++ b/net/core/sock_map.c
@@ -1569,7 +1569,7 @@ static struct bpf_iter_reg sock_map_iter
 	.ctx_arg_info_size	= 2,
 	.ctx_arg_info		= {
 		{ offsetof(struct bpf_iter__sockmap, key),
-		  PTR_TO_RDONLY_BUF | PTR_MAYBE_NULL },
+		  PTR_TO_BUF | PTR_MAYBE_NULL | MEM_RDONLY },
 		{ offsetof(struct bpf_iter__sockmap, sk),
 		  PTR_TO_BTF_ID_OR_NULL },
 	},