Merge branch 'introduce-bpf_dynptr_copy-kfunc'

Mykyta Yatsenko says:

====================
introduce bpf_dynptr_copy kfunc

From: Mykyta Yatsenko <yatsenko@meta.com>

Introduce a new kfunc, bpf_dynptr_copy, which enables copying of
data from one dynptr to another. This functionality may be useful in
scenarios such as capturing XDP data to a ring buffer.
The patch set is split into 3 patches:
1. Refactor bpf_dynptr_read and bpf_dynptr_write by extracting code into
static functions, that allows calling them with no compiler warnings
2. Introduce bpf_dynptr_copy
3. Add tests for bpf_dynptr_copy

v2->v3:
  * Implemented bpf_memcmp in dynptr_success.c test, as __builtin_memcmp
  was not inlined on GCC-BPF.
====================

Link: https://patch.msgid.link/20250226183201.332713-1-mykyta.yatsenko5@gmail.com
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/helpers.c

@@ -1759,8 +1759,8 @@ static const struct bpf_func_proto bpf_dynptr_from_mem_proto = {
 	.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,
-	   u32, offset, u64, flags)
+static int __bpf_dynptr_read(void *dst, u32 len, const struct bpf_dynptr_kern *src,
+			     u32 offset, u64 flags)
 {
 	enum bpf_dynptr_type type;
 	int err;
@@ -1793,6 +1793,12 @@ BPF_CALL_5(bpf_dynptr_read, void *, dst, u32, len, const struct bpf_dynptr_kern
 	}
 }
 
+BPF_CALL_5(bpf_dynptr_read, void *, dst, u32, len, const struct bpf_dynptr_kern *, src,
+	   u32, offset, u64, flags)
+{
+	return __bpf_dynptr_read(dst, len, src, offset, flags);
+}
+
 static const struct bpf_func_proto bpf_dynptr_read_proto = {
 	.func		= bpf_dynptr_read,
 	.gpl_only	= false,
@@ -1804,8 +1810,8 @@ static const struct bpf_func_proto bpf_dynptr_read_proto = {
 	.arg5_type	= ARG_ANYTHING,
 };
 
-BPF_CALL_5(bpf_dynptr_write, const struct bpf_dynptr_kern *, dst, u32, offset, void *, src,
-	   u32, len, u64, flags)
+static int __bpf_dynptr_write(const struct bpf_dynptr_kern *dst, u32 offset, void *src,
+			      u32 len, u64 flags)
 {
 	enum bpf_dynptr_type type;
 	int err;
@@ -1843,6 +1849,12 @@ BPF_CALL_5(bpf_dynptr_write, const struct bpf_dynptr_kern *, dst, u32, offset, v
 	}
 }
 
+BPF_CALL_5(bpf_dynptr_write, const struct bpf_dynptr_kern *, dst, u32, offset, void *, src,
+	   u32, len, u64, flags)
+{
+	return __bpf_dynptr_write(dst, offset, src, len, flags);
+}
+
 static const struct bpf_func_proto bpf_dynptr_write_proto = {
 	.func		= bpf_dynptr_write,
 	.gpl_only	= false,
@@ -2758,6 +2770,61 @@ __bpf_kfunc int bpf_dynptr_clone(const struct bpf_dynptr *p,
 	return 0;
 }
 
+/**
+ * bpf_dynptr_copy() - Copy data from one dynptr to another.
+ * @dst_ptr: Destination dynptr - where data should be copied to
+ * @dst_off: Offset into the destination dynptr
+ * @src_ptr: Source dynptr - where data should be copied from
+ * @src_off: Offset into the source dynptr
+ * @size: Length of the data to copy from source to destination
+ *
+ * Copies data from source dynptr to destination dynptr.
+ * Returns 0 on success; negative error, otherwise.
+ */
+__bpf_kfunc int bpf_dynptr_copy(struct bpf_dynptr *dst_ptr, u32 dst_off,
+				struct bpf_dynptr *src_ptr, u32 src_off, u32 size)
+{
+	struct bpf_dynptr_kern *dst = (struct bpf_dynptr_kern *)dst_ptr;
+	struct bpf_dynptr_kern *src = (struct bpf_dynptr_kern *)src_ptr;
+	void *src_slice, *dst_slice;
+	char buf[256];
+	u32 off;
+
+	src_slice = bpf_dynptr_slice(src_ptr, src_off, NULL, size);
+	dst_slice = bpf_dynptr_slice_rdwr(dst_ptr, dst_off, NULL, size);
+
+	if (src_slice && dst_slice) {
+		memmove(dst_slice, src_slice, size);
+		return 0;
+	}
+
+	if (src_slice)
+		return __bpf_dynptr_write(dst, dst_off, src_slice, size, 0);
+
+	if (dst_slice)
+		return __bpf_dynptr_read(dst_slice, size, src, src_off, 0);
+
+	if (bpf_dynptr_check_off_len(dst, dst_off, size) ||
+	    bpf_dynptr_check_off_len(src, src_off, size))
+		return -E2BIG;
+
+	off = 0;
+	while (off < size) {
+		u32 chunk_sz = min_t(u32, sizeof(buf), size - off);
+		int err;
+
+		err = __bpf_dynptr_read(buf, chunk_sz, src, src_off + off, 0);
+		if (err)
+			return err;
+		err = __bpf_dynptr_write(dst, dst_off + off, buf, chunk_sz, 0);
+		if (err)
+			return err;
+
+		off += chunk_sz;
+	}
+	return 0;
+}
+
 __bpf_kfunc void *bpf_cast_to_kern_ctx(void *obj)
 {
 	return obj;
@@ -3206,6 +3273,7 @@ BTF_ID_FLAGS(func, bpf_dynptr_is_null)
 BTF_ID_FLAGS(func, bpf_dynptr_is_rdonly)
 BTF_ID_FLAGS(func, bpf_dynptr_size)
 BTF_ID_FLAGS(func, bpf_dynptr_clone)
+BTF_ID_FLAGS(func, bpf_dynptr_copy)
 #ifdef CONFIG_NET
 BTF_ID_FLAGS(func, bpf_modify_return_test_tp)
 #endif

tools/testing/selftests/bpf/prog_tests/dynptr.c

@@ -10,6 +10,7 @@ enum test_setup_type {
 	SETUP_SYSCALL_SLEEP,
 	SETUP_SKB_PROG,
 	SETUP_SKB_PROG_TP,
+	SETUP_XDP_PROG,
 };
 
 static struct {
@@ -18,6 +19,8 @@ static struct {
 } success_tests[] = {
 	{"test_read_write", SETUP_SYSCALL_SLEEP},
 	{"test_dynptr_data", SETUP_SYSCALL_SLEEP},
+	{"test_dynptr_copy", SETUP_SYSCALL_SLEEP},
+	{"test_dynptr_copy_xdp", SETUP_XDP_PROG},
 	{"test_ringbuf", SETUP_SYSCALL_SLEEP},
 	{"test_skb_readonly", SETUP_SKB_PROG},
 	{"test_dynptr_skb_data", SETUP_SKB_PROG},
@@ -120,6 +123,24 @@ static void verify_success(const char *prog_name, enum test_setup_type setup_typ
 
 		break;
 	}
+	case SETUP_XDP_PROG:
+	{
+		char data[5000];
+		int err, prog_fd;
+		LIBBPF_OPTS(bpf_test_run_opts, opts,
+			    .data_in = &data,
+			    .data_size_in = sizeof(data),
+			    .repeat = 1,
+		);
+
+		prog_fd = bpf_program__fd(prog);
+		err = bpf_prog_test_run_opts(prog_fd, &opts);
+
+		if (!ASSERT_OK(err, "test_run"))
+			goto cleanup;
+
+		break;
+	}
 	}
 
 	ASSERT_EQ(skel->bss->err, 0, "err");

tools/testing/selftests/bpf/progs/dynptr_success.c

@@ -1,20 +1,19 @@
 // SPDX-License-Identifier: GPL-2.0
 /* Copyright (c) 2022 Facebook */
 
+#include <vmlinux.h>
 #include <string.h>
 #include <stdbool.h>
-#include <linux/bpf.h>
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_tracing.h>
 #include "bpf_misc.h"
-#include "bpf_kfuncs.h"
 #include "errno.h"
 
 char _license[] SEC("license") = "GPL";
 
 int pid, err, val;
 
-struct sample {
+struct ringbuf_sample {
 	int pid;
 	int seq;
 	long value;
@@ -121,7 +120,7 @@ int test_dynptr_data(void *ctx)
 
 static int ringbuf_callback(__u32 index, void *data)
 {
-	struct sample *sample;
+	struct ringbuf_sample *sample;
 
 	struct bpf_dynptr *ptr = (struct bpf_dynptr *)data;
 
@@ -138,7 +137,7 @@ SEC("?tp/syscalls/sys_enter_nanosleep")
 int test_ringbuf(void *ctx)
 {
 	struct bpf_dynptr ptr;
-	struct sample *sample;
+	struct ringbuf_sample *sample;
 
 	if (bpf_get_current_pid_tgid() >> 32 != pid)
 		return 0;
@@ -567,3 +566,117 @@ int BPF_PROG(test_dynptr_skb_tp_btf, void *skb, void *location)
 
 	return 1;
 }
+
+static inline int bpf_memcmp(const char *a, const char *b, u32 size)
+{
+	int i;
+
+	bpf_for(i, 0, size) {
+		if (a[i] != b[i])
+			return a[i] < b[i] ? -1 : 1;
+	}
+	return 0;
+}
+
+SEC("?tp/syscalls/sys_enter_nanosleep")
+int test_dynptr_copy(void *ctx)
+{
+	char data[] = "hello there, world!!";
+	char buf[32] = {'\0'};
+	__u32 sz = sizeof(data);
+	struct bpf_dynptr src, dst;
+
+	bpf_ringbuf_reserve_dynptr(&ringbuf, sz, 0, &src);
+	bpf_ringbuf_reserve_dynptr(&ringbuf, sz, 0, &dst);
+
+	/* Test basic case of copying contiguous memory backed dynptrs */
+	err = bpf_dynptr_write(&src, 0, data, sz, 0);
+	err = err ?: bpf_dynptr_copy(&dst, 0, &src, 0, sz);
+	err = err ?: bpf_dynptr_read(buf, sz, &dst, 0, 0);
+	err = err ?: bpf_memcmp(data, buf, sz);
+
+	/* Test that offsets are handled correctly */
+	err = err ?: bpf_dynptr_copy(&dst, 3, &src, 5, sz - 5);
+	err = err ?: bpf_dynptr_read(buf, sz - 5, &dst, 3, 0);
+	err = err ?: bpf_memcmp(data + 5, buf, sz - 5);
+
+	bpf_ringbuf_discard_dynptr(&src, 0);
+	bpf_ringbuf_discard_dynptr(&dst, 0);
+	return 0;
+}
+
+SEC("xdp")
+int test_dynptr_copy_xdp(struct xdp_md *xdp)
+{
+	struct bpf_dynptr ptr_buf, ptr_xdp;
+	char data[] = "qwertyuiopasdfghjkl";
+	char buf[32] = {'\0'};
+	__u32 len = sizeof(data);
+	int i, chunks = 200;
+
+	/* ptr_xdp is backed by non-contiguous memory */
+	bpf_dynptr_from_xdp(xdp, 0, &ptr_xdp);
+	bpf_ringbuf_reserve_dynptr(&ringbuf, len * chunks, 0, &ptr_buf);
+
+	/* Destination dynptr is backed by non-contiguous memory */
+	bpf_for(i, 0, chunks) {
+		err = bpf_dynptr_write(&ptr_buf, i * len, data, len, 0);
+		if (err)
+			goto out;
+	}
+
+	err = bpf_dynptr_copy(&ptr_xdp, 0, &ptr_buf, 0, len * chunks);
+	if (err)
+		goto out;
+
+	bpf_for(i, 0, chunks) {
+		__builtin_memset(buf, 0, sizeof(buf));
+		err = bpf_dynptr_read(&buf, len, &ptr_xdp, i * len, 0);
+		if (err)
+			goto out;
+		if (bpf_memcmp(data, buf, len) != 0)
+			goto out;
+	}
+
+	/* Source dynptr is backed by non-contiguous memory */
+	__builtin_memset(buf, 0, sizeof(buf));
+	bpf_for(i, 0, chunks) {
+		err = bpf_dynptr_write(&ptr_buf, i * len, buf, len, 0);
+		if (err)
+			goto out;
+	}
+
+	err = bpf_dynptr_copy(&ptr_buf, 0, &ptr_xdp, 0, len * chunks);
+	if (err)
+		goto out;
+
+	bpf_for(i, 0, chunks) {
+		__builtin_memset(buf, 0, sizeof(buf));
+		err = bpf_dynptr_read(&buf, len, &ptr_buf, i * len, 0);
+		if (err)
+			goto out;
+		if (bpf_memcmp(data, buf, len) != 0)
+			goto out;
+	}
+
+	/* Both source and destination dynptrs are backed by non-contiguous memory */
+	err = bpf_dynptr_copy(&ptr_xdp, 2, &ptr_xdp, len, len * (chunks - 1));
+	if (err)
+		goto out;
+
+	bpf_for(i, 0, chunks - 1) {
+		__builtin_memset(buf, 0, sizeof(buf));
+		err = bpf_dynptr_read(&buf, len, &ptr_xdp, 2 + i * len, 0);
+		if (err)
+			goto out;
+		if (bpf_memcmp(data, buf, len) != 0)
+			goto out;
+	}
+
+	if (bpf_dynptr_copy(&ptr_xdp, 2000, &ptr_xdp, 0, len * chunks) != -E2BIG)
+		err = 1;
+
+out:
+	bpf_ringbuf_discard_dynptr(&ptr_buf, 0);
+	return XDP_DROP;
+}