[PATCH 6.1 50/92] bpf: Add MEM_WRITE attribute

15 Jan 2025

6.1-stable review patch.  If anyone has any objections, please let me know.
------------------
From: Daniel Borkmann daniel@iogearbox.net
commit 6fad274f06f038c29660aa53fbad14241c9fd976 upstream.
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
Signed-off-by: BRUNO VERNAY bruno.vernay@se.com
Signed-off-by: Hugo SIMELIERE hsimeliere.opensource@witekio.com
Stable-dep-of: 8ea607330a39 ("bpf: Fix overloading of MEM_UNINIT's meaning")
Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
---
 include/linux/bpf.h      |   14 +++++++++++---
 kernel/bpf/helpers.c     |   10 +++++-----
 kernel/bpf/ringbuf.c     |    2 +-
 kernel/bpf/syscall.c     |    2 +-
 kernel/trace/bpf_trace.c |    4 ++--
 net/core/filter.c        |    4 ++--
 6 files changed, 22 insertions(+), 14 deletions(-)

--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -464,6 +464,7 @@ 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. */
@@ -480,6 +481,13 @@ 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,
 };
@@ -537,10 +545,10 @@ enum bpf_arg_type {
    ARG_PTR_TO_ALLOC_MEM_OR_NULL	= PTR_MAYBE_NULL | ARG_PTR_TO_ALLOC_MEM,
    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,
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -107,7 +107,7 @@ const struct bpf_func_proto bpf_map_pop_
    .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)
@@ -120,7 +120,7 @@ const struct bpf_func_proto bpf_map_peek
    .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)
@@ -531,7 +531,7 @@ const struct bpf_func_proto bpf_strtol_p
    .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),
 };
@@ -561,7 +561,7 @@ const struct bpf_func_proto bpf_strtoul_
    .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),
 };
@@ -1502,7 +1502,7 @@ static const struct bpf_func_proto bpf_d
    .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, struct bpf_dynptr_kern *, src,
--- a/kernel/bpf/ringbuf.c
+++ b/kernel/bpf/ringbuf.c
@@ -618,7 +618,7 @@ const struct bpf_func_proto bpf_ringbuf_
    .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)
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -5265,7 +5265,7 @@ static const struct bpf_func_proto bpf_k
    .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),
 };
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1192,7 +1192,7 @@ static const struct bpf_func_proto bpf_g
    .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),
 };
@@ -1209,7 +1209,7 @@ static const struct bpf_func_proto bpf_g
    .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),
 };
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -6243,7 +6243,7 @@ static const struct bpf_func_proto bpf_s
    .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,
@@ -6255,7 +6255,7 @@ static const struct bpf_func_proto bpf_x
    .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,

    

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[PATCH 6.1 50/92] bpf: Add MEM_WRITE attribute