[bpf-next,v5,3/9] bpf: Fix helper writes to read-only maps

Commit Message

Daniel Borkmann Sept. 13, 2024, 7:17 p.m. UTC

Lonial found an issue that despite user- and BPF-side frozen BPF map
(like in case of .rodata), it was still possible to write into it from
a BPF program side through specific helpers having ARG_PTR_TO_{LONG,INT}
as arguments.

In check_func_arg() when the argument is as mentioned, the meta->raw_mode
is never set. Later, check_helper_mem_access(), under the case of
PTR_TO_MAP_VALUE as register base type, it assumes BPF_READ for the
subsequent call to check_map_access_type() and given the BPF map is
read-only it succeeds.

The helpers really need to be annotated as ARG_PTR_TO_{LONG,INT} | MEM_UNINIT
when results are written into them as opposed to read out of them. The
latter indicates that it's okay to pass a pointer to uninitialized memory
as the memory is written to anyway.

However, ARG_PTR_TO_{LONG,INT} is a special case of ARG_PTR_TO_FIXED_SIZE_MEM
just with additional alignment requirement. So it is better to just get
rid of the ARG_PTR_TO_{LONG,INT} special cases altogether and reuse the
fixed size memory types. For this, add MEM_ALIGNED to additionally ensure
alignment given these helpers write directly into the args via *<ptr> = val.
The .arg*_size has been initialized reflecting the actual sizeof(*<ptr>).

MEM_ALIGNED can only be used in combination with MEM_FIXED_SIZE annotated
argument types, since in !MEM_FIXED_SIZE cases the verifier does not know
the buffer size a priori and therefore cannot blindly write *<ptr> = val.

Fixes: 57c3bb725a3d ("bpf: Introduce ARG_PTR_TO_{INT,LONG} arg types")
Reported-by: Lonial Con <[e-mail]>
Signed-off-by: Daniel Borkmann <[e-mail]>
Acked-by: Andrii Nakryiko <[e-mail]>
Acked-by: Shung-Hsi Yu <[e-mail]>
---
 v1 -> v2:
 - switch to MEM_FIXED_SIZE
 v3 -> v4:
 - fixed 64bit in strto{u,}l (Alexei)
 v4 -> v5:
 - line breaks (Andrii)

 include/linux/bpf.h      |  7 +++++--
 kernel/bpf/helpers.c     |  6 ++++--
 kernel/bpf/syscall.c     |  3 ++-
 kernel/bpf/verifier.c    | 41 +++++-----------------------------------
 kernel/trace/bpf_trace.c |  6 ++++--
 net/core/filter.c        |  6 ++++--
 6 files changed, 24 insertions(+), 45 deletions(-)

Patch

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 6f87fb014fba..6a61ed4266b6 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -695,6 +695,11 @@  enum bpf_type_flag {
 	/* DYNPTR points to xdp_buff */
 	DYNPTR_TYPE_XDP		= BIT(16 + BPF_BASE_TYPE_BITS),
 
+	/* Memory must be aligned on some architectures, used in combination with
+	 * MEM_FIXED_SIZE.
+	 */
+	MEM_ALIGNED		= BIT(17 + BPF_BASE_TYPE_BITS),
+
 	__BPF_TYPE_FLAG_MAX,
 	__BPF_TYPE_LAST_FLAG	= __BPF_TYPE_FLAG_MAX - 1,
 };
@@ -732,8 +737,6 @@  enum bpf_arg_type {
 	ARG_ANYTHING,		/* any (initialized) argument is ok */
 	ARG_PTR_TO_SPIN_LOCK,	/* pointer to bpf_spin_lock */
 	ARG_PTR_TO_SOCK_COMMON,	/* pointer to sock_common */
-	ARG_PTR_TO_INT,		/* pointer to int */
-	ARG_PTR_TO_LONG,	/* pointer to long */
 	ARG_PTR_TO_SOCKET,	/* pointer to bpf_sock (fullsock) */
 	ARG_PTR_TO_BTF_ID,	/* pointer to in-kernel struct */
 	ARG_PTR_TO_RINGBUF_MEM,	/* pointer to dynamically reserved ringbuf memory */
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 5404bb964d83..5e97fdc6b20f 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -537,7 +537,8 @@  const struct bpf_func_proto bpf_strtol_proto = {
 	.arg1_type	= ARG_PTR_TO_MEM | MEM_RDONLY,
 	.arg2_type	= ARG_CONST_SIZE,
 	.arg3_type	= ARG_ANYTHING,
-	.arg4_type	= ARG_PTR_TO_LONG,
+	.arg4_type	= ARG_PTR_TO_FIXED_SIZE_MEM | MEM_UNINIT | MEM_ALIGNED,
+	.arg4_size	= sizeof(s64),
 };
 
 BPF_CALL_4(bpf_strtoul, const char *, buf, size_t, buf_len, u64, flags,
@@ -563,7 +564,8 @@  const struct bpf_func_proto bpf_strtoul_proto = {
 	.arg1_type	= ARG_PTR_TO_MEM | MEM_RDONLY,
 	.arg2_type	= ARG_CONST_SIZE,
 	.arg3_type	= ARG_ANYTHING,
-	.arg4_type	= ARG_PTR_TO_LONG,
+	.arg4_type	= ARG_PTR_TO_FIXED_SIZE_MEM | MEM_UNINIT | MEM_ALIGNED,
+	.arg4_size	= sizeof(u64),
 };
 
 BPF_CALL_3(bpf_strncmp, const char *, s1, u32, s1_sz, const char *, s2)
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 6988e432fc3d..a7cd3719e26a 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -5954,7 +5954,8 @@  static const struct bpf_func_proto bpf_kallsyms_lookup_name_proto = {
 	.arg1_type	= ARG_PTR_TO_MEM,
 	.arg2_type	= ARG_CONST_SIZE_OR_ZERO,
 	.arg3_type	= ARG_ANYTHING,
-	.arg4_type	= ARG_PTR_TO_LONG,
+	.arg4_type	= ARG_PTR_TO_FIXED_SIZE_MEM | MEM_UNINIT | MEM_ALIGNED,
+	.arg4_size	= sizeof(u64),
 };
 
 static const struct bpf_func_proto *
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index f35b80c16cda..2d8af74994ae 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -8301,16 +8301,6 @@  static bool arg_type_is_dynptr(enum bpf_arg_type type)
 	return base_type(type) == ARG_PTR_TO_DYNPTR;
 }
 
-static int int_ptr_type_to_size(enum bpf_arg_type type)
-{
-	if (type == ARG_PTR_TO_INT)
-		return sizeof(u32);
-	else if (type == ARG_PTR_TO_LONG)
-		return sizeof(u64);
-
-	return -EINVAL;
-}
-
 static int resolve_map_arg_type(struct bpf_verifier_env *env,
 				 const struct bpf_call_arg_meta *meta,
 				 enum bpf_arg_type *arg_type)
@@ -8383,16 +8373,6 @@  static const struct bpf_reg_types mem_types = {
 	},
 };
 
-static const struct bpf_reg_types int_ptr_types = {
-	.types = {
-		PTR_TO_STACK,
-		PTR_TO_PACKET,
-		PTR_TO_PACKET_META,
-		PTR_TO_MAP_KEY,
-		PTR_TO_MAP_VALUE,
-	},
-};
-
 static const struct bpf_reg_types spin_lock_types = {
 	.types = {
 		PTR_TO_MAP_VALUE,
@@ -8453,8 +8433,6 @@  static const struct bpf_reg_types *compatible_reg_types[__BPF_ARG_TYPE_MAX] = {
 	[ARG_PTR_TO_SPIN_LOCK]		= &spin_lock_types,
 	[ARG_PTR_TO_MEM]		= &mem_types,
 	[ARG_PTR_TO_RINGBUF_MEM]	= &ringbuf_mem_types,
-	[ARG_PTR_TO_INT]		= &int_ptr_types,
-	[ARG_PTR_TO_LONG]		= &int_ptr_types,
 	[ARG_PTR_TO_PERCPU_BTF_ID]	= &percpu_btf_ptr_types,
 	[ARG_PTR_TO_FUNC]		= &func_ptr_types,
 	[ARG_PTR_TO_STACK]		= &stack_ptr_types,
@@ -9017,9 +8995,11 @@  static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
 		 */
 		meta->raw_mode = arg_type & MEM_UNINIT;
 		if (arg_type & MEM_FIXED_SIZE) {
-			err = check_helper_mem_access(env, regno,
-						      fn->arg_size[arg], false,
-						      meta);
+			err = check_helper_mem_access(env, regno, fn->arg_size[arg], false, meta);
+			if (err)
+				return err;
+			if (arg_type & MEM_ALIGNED)
+				err = check_ptr_alignment(env, reg, 0, fn->arg_size[arg], true);
 		}
 		break;
 	case ARG_CONST_SIZE:
@@ -9044,17 +9024,6 @@  static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
 		if (err)
 			return err;
 		break;
-	case ARG_PTR_TO_INT:
-	case ARG_PTR_TO_LONG:
-	{
-		int size = int_ptr_type_to_size(arg_type);
-
-		err = check_helper_mem_access(env, regno, size, false, meta);
-		if (err)
-			return err;
-		err = check_ptr_alignment(env, reg, 0, size, true);
-		break;
-	}
 	case ARG_PTR_TO_CONST_STR:
 	{
 		err = check_reg_const_str(env, reg, regno);
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 98e395f1baae..843bb0ca6f20 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1202,7 +1202,8 @@  static const struct bpf_func_proto bpf_get_func_arg_proto = {
 	.ret_type	= RET_INTEGER,
 	.arg1_type	= ARG_PTR_TO_CTX,
 	.arg2_type	= ARG_ANYTHING,
-	.arg3_type	= ARG_PTR_TO_LONG,
+	.arg3_type	= ARG_PTR_TO_FIXED_SIZE_MEM | MEM_UNINIT | MEM_ALIGNED,
+	.arg3_size	= sizeof(u64),
 };
 
 BPF_CALL_2(get_func_ret, void *, ctx, u64 *, value)
@@ -1218,7 +1219,8 @@  static const struct bpf_func_proto bpf_get_func_ret_proto = {
 	.func		= get_func_ret,
 	.ret_type	= RET_INTEGER,
 	.arg1_type	= ARG_PTR_TO_CTX,
-	.arg2_type	= ARG_PTR_TO_LONG,
+	.arg2_type	= ARG_PTR_TO_FIXED_SIZE_MEM | MEM_UNINIT | MEM_ALIGNED,
+	.arg2_size	= sizeof(u64),
 };
 
 BPF_CALL_1(get_func_arg_cnt, void *, ctx)
diff --git a/net/core/filter.c b/net/core/filter.c
index ecf2ddf633bf..d0550c87e520 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -6346,7 +6346,8 @@  static const struct bpf_func_proto bpf_skb_check_mtu_proto = {
 	.ret_type	= RET_INTEGER,
 	.arg1_type      = ARG_PTR_TO_CTX,
 	.arg2_type      = ARG_ANYTHING,
-	.arg3_type      = ARG_PTR_TO_INT,
+	.arg3_type      = ARG_PTR_TO_FIXED_SIZE_MEM | MEM_UNINIT | MEM_ALIGNED,
+	.arg3_size	= sizeof(u32),
 	.arg4_type      = ARG_ANYTHING,
 	.arg5_type      = ARG_ANYTHING,
 };
@@ -6357,7 +6358,8 @@  static const struct bpf_func_proto bpf_xdp_check_mtu_proto = {
 	.ret_type	= RET_INTEGER,
 	.arg1_type      = ARG_PTR_TO_CTX,
 	.arg2_type      = ARG_ANYTHING,
-	.arg3_type      = ARG_PTR_TO_INT,
+	.arg3_type      = ARG_PTR_TO_FIXED_SIZE_MEM | MEM_UNINIT | MEM_ALIGNED,
+	.arg3_size	= sizeof(u32),
 	.arg4_type      = ARG_ANYTHING,
 	.arg5_type      = ARG_ANYTHING,
 };