bpf: Add MEM_WRITE attribute

Add a MEM_WRITE attribute for BPF helper functions which can be used in
bpf_func_proto to annotate an argument type in order to let the verifier
know that the helper writes into the memory passed as an argument. In
the past MEM_UNINIT has been (ab)used for this function, but the latter
merely tells the verifier that the passed memory can be uninitialized.

There have been bugs with overloading the latter but aside from that
there are also cases where the passed memory is read + written which
currently cannot be expressed, see also 4b3786a6c539 ("bpf: Zero former
ARG_PTR_TO_{LONG,INT} args in case of error").

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20241021152809.33343-1-daniel@iogearbox.net
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 19d8ca8..bdadb0b 100644 (file)
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -635,6 +635,7 @@ enum bpf_type_flag {
         */
        PTR_UNTRUSTED           = BIT(6 + BPF_BASE_TYPE_BITS),
 
+       /* MEM can be uninitialized. */
        MEM_UNINIT              = BIT(7 + BPF_BASE_TYPE_BITS),
 
        /* DYNPTR points to memory local to the bpf program. */
@@ -700,6 +701,13 @@ enum bpf_type_flag {
         */
        MEM_ALIGNED             = BIT(17 + BPF_BASE_TYPE_BITS),
 
+       /* MEM is being written to, often combined with MEM_UNINIT. Non-presence
+        * of MEM_WRITE means that MEM is only being read. MEM_WRITE without the
+        * MEM_UNINIT means that memory needs to be initialized since it is also
+        * read.
+        */
+       MEM_WRITE               = BIT(18 + BPF_BASE_TYPE_BITS),
+
        __BPF_TYPE_FLAG_MAX,
        __BPF_TYPE_LAST_FLAG    = __BPF_TYPE_FLAG_MAX - 1,
 };
@@ -758,10 +766,10 @@ enum bpf_arg_type {
        ARG_PTR_TO_SOCKET_OR_NULL       = PTR_MAYBE_NULL | ARG_PTR_TO_SOCKET,
        ARG_PTR_TO_STACK_OR_NULL        = PTR_MAYBE_NULL | ARG_PTR_TO_STACK,
        ARG_PTR_TO_BTF_ID_OR_NULL       = PTR_MAYBE_NULL | ARG_PTR_TO_BTF_ID,
-       /* pointer to memory does not need to be initialized, helper function must fill
-        * all bytes or clear them in error case.
+       /* Pointer to memory does not need to be initialized, since helper function
+        * fills all bytes or clears them in error case.
         */
-       ARG_PTR_TO_UNINIT_MEM           = MEM_UNINIT | ARG_PTR_TO_MEM,
+       ARG_PTR_TO_UNINIT_MEM           = MEM_UNINIT | MEM_WRITE | ARG_PTR_TO_MEM,
        /* Pointer to valid memory of size known at compile time. */
        ARG_PTR_TO_FIXED_SIZE_MEM       = MEM_FIXED_SIZE | ARG_PTR_TO_MEM,
 

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 1a43d06..ca3f0a2 100644 (file)
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -111,7 +111,7 @@ const struct bpf_func_proto bpf_map_pop_elem_proto = {
        .gpl_only       = false,
        .ret_type       = RET_INTEGER,
        .arg1_type      = ARG_CONST_MAP_PTR,
-       .arg2_type      = ARG_PTR_TO_MAP_VALUE | MEM_UNINIT,
+       .arg2_type      = ARG_PTR_TO_MAP_VALUE | MEM_UNINIT | MEM_WRITE,
 };
 
 BPF_CALL_2(bpf_map_peek_elem, struct bpf_map *, map, void *, value)
@@ -124,7 +124,7 @@ const struct bpf_func_proto bpf_map_peek_elem_proto = {
        .gpl_only       = false,
        .ret_type       = RET_INTEGER,
        .arg1_type      = ARG_CONST_MAP_PTR,
-       .arg2_type      = ARG_PTR_TO_MAP_VALUE | MEM_UNINIT,
+       .arg2_type      = ARG_PTR_TO_MAP_VALUE | MEM_UNINIT | MEM_WRITE,
 };
 
 BPF_CALL_3(bpf_map_lookup_percpu_elem, struct bpf_map *, map, void *, key, u32, cpu)
@@ -538,7 +538,7 @@ 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_FIXED_SIZE_MEM | MEM_UNINIT | MEM_ALIGNED,
+       .arg4_type      = ARG_PTR_TO_FIXED_SIZE_MEM | MEM_UNINIT | MEM_WRITE | MEM_ALIGNED,
        .arg4_size      = sizeof(s64),
 };
 
@@ -566,7 +566,7 @@ 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_FIXED_SIZE_MEM | MEM_UNINIT | MEM_ALIGNED,
+       .arg4_type      = ARG_PTR_TO_FIXED_SIZE_MEM | MEM_UNINIT | MEM_WRITE | MEM_ALIGNED,
        .arg4_size      = sizeof(u64),
 };
 
@@ -1742,7 +1742,7 @@ static const struct bpf_func_proto bpf_dynptr_from_mem_proto = {
        .arg1_type      = ARG_PTR_TO_UNINIT_MEM,
        .arg2_type      = ARG_CONST_SIZE_OR_ZERO,
        .arg3_type      = ARG_ANYTHING,
-       .arg4_type      = ARG_PTR_TO_DYNPTR | DYNPTR_TYPE_LOCAL | MEM_UNINIT,
+       .arg4_type      = ARG_PTR_TO_DYNPTR | DYNPTR_TYPE_LOCAL | MEM_UNINIT | MEM_WRITE,
 };
 
 BPF_CALL_5(bpf_dynptr_read, void *, dst, u32, len, const struct bpf_dynptr_kern *, src,

diff --git a/kernel/bpf/ringbuf.c b/kernel/bpf/ringbuf.c
index de3b681..e1cfe89 100644 (file)
--- a/kernel/bpf/ringbuf.c
+++ b/kernel/bpf/ringbuf.c
@@ -632,7 +632,7 @@ const struct bpf_func_proto bpf_ringbuf_reserve_dynptr_proto = {
        .arg1_type      = ARG_CONST_MAP_PTR,
        .arg2_type      = ARG_ANYTHING,
        .arg3_type      = ARG_ANYTHING,
-       .arg4_type      = ARG_PTR_TO_DYNPTR | DYNPTR_TYPE_RINGBUF | MEM_UNINIT,
+       .arg4_type      = ARG_PTR_TO_DYNPTR | DYNPTR_TYPE_RINGBUF | MEM_UNINIT | MEM_WRITE,
 };
 
 BPF_CALL_2(bpf_ringbuf_submit_dynptr, struct bpf_dynptr_kern *, ptr, u64, flags)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 8cfa718..6717952 100644 (file)
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -5892,7 +5892,7 @@ 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_FIXED_SIZE_MEM | MEM_UNINIT | MEM_ALIGNED,
+       .arg4_type      = ARG_PTR_TO_FIXED_SIZE_MEM | MEM_UNINIT | MEM_WRITE | MEM_ALIGNED,
        .arg4_size      = sizeof(u64),
 };
 

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 3bd402f..95b6b3b 100644 (file)
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1202,7 +1202,7 @@ 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_FIXED_SIZE_MEM | MEM_UNINIT | MEM_ALIGNED,
+       .arg3_type      = ARG_PTR_TO_FIXED_SIZE_MEM | MEM_UNINIT | MEM_WRITE | MEM_ALIGNED,
        .arg3_size      = sizeof(u64),
 };
 
@@ -1219,7 +1219,7 @@ 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_FIXED_SIZE_MEM | MEM_UNINIT | MEM_ALIGNED,
+       .arg2_type      = ARG_PTR_TO_FIXED_SIZE_MEM | MEM_UNINIT | MEM_WRITE | MEM_ALIGNED,
        .arg2_size      = sizeof(u64),
 };
 

diff --git a/net/core/filter.c b/net/core/filter.c
index cb272b3..16b324d 100644 (file)
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -6368,7 +6368,7 @@ 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_FIXED_SIZE_MEM | MEM_UNINIT | MEM_ALIGNED,
+       .arg3_type      = ARG_PTR_TO_FIXED_SIZE_MEM | MEM_UNINIT | MEM_WRITE | MEM_ALIGNED,
        .arg3_size      = sizeof(u32),
        .arg4_type      = ARG_ANYTHING,
        .arg5_type      = ARG_ANYTHING,
@@ -6380,7 +6380,7 @@ 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_FIXED_SIZE_MEM | MEM_UNINIT | MEM_ALIGNED,
+       .arg3_type      = ARG_PTR_TO_FIXED_SIZE_MEM | MEM_UNINIT | MEM_WRITE | MEM_ALIGNED,
        .arg3_size      = sizeof(u32),
        .arg4_type      = ARG_ANYTHING,
        .arg5_type      = ARG_ANYTHING,