Merge branch 'introduce-kfuncs-for-memory-reads-into-dynptrs'

Mykyta Yatsenko says:

====================
Introduce kfuncs for memory reads into dynptrs

From: Mykyta Yatsenko <yatsenko@meta.com>

This patch adds new kfuncs that enable reading variable-length
user or kernel data directly into dynptrs.
These kfuncs provide a way to perform dynamically-sized reads
while maintaining memory safety. Unlike existing
`bpf_probe_read_{user|kernel}` APIs, which are limited to constant-sized
reads, these new kfuncs allow for more flexible data access.

v4 -> v5
 * Fix pointers annotations, use __user where necessary, cast where needed

v3 -> v4
 * Added pid filtering in selftests

v2 -> v3
 * Add KF_TRUSTED_ARGS for kfuncs that take pointer to task_struct
 as an argument
 * Remove checks for non-NULL task, where it was not necessary
 * Added comments on constants used in selftests, etc.

v1 -> v2
 * Renaming helper functions to use "user_str" instead of "user_data_str"
 suffix

====================

Link: https://patch.msgid.link/20250512205348.191079-1-mykyta.yatsenko5@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

2 files changed, 204 insertions, 12 deletions

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index fed53da75025..ebb604e39eb1 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -1714,16 +1714,6 @@ void bpf_dynptr_set_null(struct bpf_dynptr_kern *ptr)
 	memset(ptr, 0, sizeof(*ptr));
 }
 
-static int bpf_dynptr_check_off_len(const struct bpf_dynptr_kern *ptr, u32 offset, u32 len)
-{
-	u32 size = __bpf_dynptr_size(ptr);
-
-	if (len > size || offset > size - len)
-		return -E2BIG;
-
-	return 0;
-}
-
 BPF_CALL_4(bpf_dynptr_from_mem, void *, data, u32, size, u64, flags, struct bpf_dynptr_kern *, ptr)
 {
 	int err;
@@ -1810,8 +1800,8 @@ static const struct bpf_func_proto bpf_dynptr_read_proto = {
 	.arg5_type	= ARG_ANYTHING,
 };
 
-static int __bpf_dynptr_write(const struct bpf_dynptr_kern *dst, u32 offset, void *src,
-			      u32 len, u64 flags)
+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;
@@ -3388,6 +3378,14 @@ BTF_ID_FLAGS(func, bpf_iter_kmem_cache_next, KF_ITER_NEXT | KF_RET_NULL | KF_SLE
 BTF_ID_FLAGS(func, bpf_iter_kmem_cache_destroy, KF_ITER_DESTROY | KF_SLEEPABLE)
 BTF_ID_FLAGS(func, bpf_local_irq_save)
 BTF_ID_FLAGS(func, bpf_local_irq_restore)
+BTF_ID_FLAGS(func, bpf_probe_read_user_dynptr)
+BTF_ID_FLAGS(func, bpf_probe_read_kernel_dynptr)
+BTF_ID_FLAGS(func, bpf_probe_read_user_str_dynptr)
+BTF_ID_FLAGS(func, bpf_probe_read_kernel_str_dynptr)
+BTF_ID_FLAGS(func, bpf_copy_from_user_dynptr, KF_SLEEPABLE)
+BTF_ID_FLAGS(func, bpf_copy_from_user_str_dynptr, KF_SLEEPABLE)
+BTF_ID_FLAGS(func, bpf_copy_from_user_task_dynptr, KF_SLEEPABLE | KF_TRUSTED_ARGS)
+BTF_ID_FLAGS(func, bpf_copy_from_user_task_str_dynptr, KF_SLEEPABLE | KF_TRUSTED_ARGS)
 BTF_KFUNCS_END(common_btf_ids)
 
 static const struct btf_kfunc_id_set common_kfunc_set = {
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 868920994517..985ce3854af8 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -3466,6 +3466,142 @@ static int __init bpf_kprobe_multi_kfuncs_init(void)
 
 late_initcall(bpf_kprobe_multi_kfuncs_init);
 
+typedef int (*copy_fn_t)(void *dst, const void *src, u32 size, struct task_struct *tsk);
+
+/*
+ * The __always_inline is to make sure the compiler doesn't
+ * generate indirect calls into callbacks, which is expensive,
+ * on some kernel configurations. This allows compiler to put
+ * direct calls into all the specific callback implementations
+ * (copy_user_data_sleepable, copy_user_data_nofault, and so on)
+ */
+static __always_inline int __bpf_dynptr_copy_str(struct bpf_dynptr *dptr, u32 doff, u32 size,
+						 const void *unsafe_src,
+						 copy_fn_t str_copy_fn,
+						 struct task_struct *tsk)
+{
+	struct bpf_dynptr_kern *dst;
+	u32 chunk_sz, off;
+	void *dst_slice;
+	int cnt, err;
+	char buf[256];
+
+	dst_slice = bpf_dynptr_slice_rdwr(dptr, doff, NULL, size);
+	if (likely(dst_slice))
+		return str_copy_fn(dst_slice, unsafe_src, size, tsk);
+
+	dst = (struct bpf_dynptr_kern *)dptr;
+	if (bpf_dynptr_check_off_len(dst, doff, size))
+		return -E2BIG;
+
+	for (off = 0; off < size; off += chunk_sz - 1) {
+		chunk_sz = min_t(u32, sizeof(buf), size - off);
+		/* Expect str_copy_fn to return count of copied bytes, including
+		 * zero terminator. Next iteration increment off by chunk_sz - 1 to
+		 * overwrite NUL.
+		 */
+		cnt = str_copy_fn(buf, unsafe_src + off, chunk_sz, tsk);
+		if (cnt < 0)
+			return cnt;
+		err = __bpf_dynptr_write(dst, doff + off, buf, cnt, 0);
+		if (err)
+			return err;
+		if (cnt < chunk_sz || chunk_sz == 1) /* we are done */
+			return off + cnt;
+	}
+	return off;
+}
+
+static __always_inline int __bpf_dynptr_copy(const struct bpf_dynptr *dptr, u32 doff,
+					     u32 size, const void *unsafe_src,
+					     copy_fn_t copy_fn, struct task_struct *tsk)
+{
+	struct bpf_dynptr_kern *dst;
+	void *dst_slice;
+	char buf[256];
+	u32 off, chunk_sz;
+	int err;
+
+	dst_slice = bpf_dynptr_slice_rdwr(dptr, doff, NULL, size);
+	if (likely(dst_slice))
+		return copy_fn(dst_slice, unsafe_src, size, tsk);
+
+	dst = (struct bpf_dynptr_kern *)dptr;
+	if (bpf_dynptr_check_off_len(dst, doff, size))
+		return -E2BIG;
+
+	for (off = 0; off < size; off += chunk_sz) {
+		chunk_sz = min_t(u32, sizeof(buf), size - off);
+		err = copy_fn(buf, unsafe_src + off, chunk_sz, tsk);
+		if (err)
+			return err;
+		err = __bpf_dynptr_write(dst, doff + off, buf, chunk_sz, 0);
+		if (err)
+			return err;
+	}
+	return 0;
+}
+
+static __always_inline int copy_user_data_nofault(void *dst, const void *unsafe_src,
+						  u32 size, struct task_struct *tsk)
+{
+	return copy_from_user_nofault(dst, (const void __user *)unsafe_src, size);
+}
+
+static __always_inline int copy_user_data_sleepable(void *dst, const void *unsafe_src,
+						    u32 size, struct task_struct *tsk)
+{
+	int ret;
+
+	if (!tsk) /* Read from the current task */
+		return copy_from_user(dst, (const void __user *)unsafe_src, size);
+
+	ret = access_process_vm(tsk, (unsigned long)unsafe_src, dst, size, 0);
+	if (ret != size)
+		return -EFAULT;
+	return 0;
+}
+
+static __always_inline int copy_kernel_data_nofault(void *dst, const void *unsafe_src,
+						    u32 size, struct task_struct *tsk)
+{
+	return copy_from_kernel_nofault(dst, unsafe_src, size);
+}
+
+static __always_inline int copy_user_str_nofault(void *dst, const void *unsafe_src,
+						 u32 size, struct task_struct *tsk)
+{
+	return strncpy_from_user_nofault(dst, (const void __user *)unsafe_src, size);
+}
+
+static __always_inline int copy_user_str_sleepable(void *dst, const void *unsafe_src,
+						   u32 size, struct task_struct *tsk)
+{
+	int ret;
+
+	if (unlikely(size == 0))
+		return 0;
+
+	if (tsk) {
+		ret = copy_remote_vm_str(tsk, (unsigned long)unsafe_src, dst, size, 0);
+	} else {
+		ret = strncpy_from_user(dst, (const void __user *)unsafe_src, size - 1);
+		/* strncpy_from_user does not guarantee NUL termination */
+		if (ret >= 0)
+			((char *)dst)[ret] = '\0';
+	}
+
+	if (ret < 0)
+		return ret;
+	return ret + 1;
+}
+
+static __always_inline int copy_kernel_str_nofault(void *dst, const void *unsafe_src,
+						   u32 size, struct task_struct *tsk)
+{
+	return strncpy_from_kernel_nofault(dst, unsafe_src, size);
+}
+
 __bpf_kfunc_start_defs();
 
 __bpf_kfunc int bpf_send_signal_task(struct task_struct *task, int sig, enum pid_type type,
@@ -3477,4 +3613,62 @@ __bpf_kfunc int bpf_send_signal_task(struct task_struct *task, int sig, enum pid
 	return bpf_send_signal_common(sig, type, task, value);
 }
 
+__bpf_kfunc int bpf_probe_read_user_dynptr(struct bpf_dynptr *dptr, u32 off,
+					   u32 size, const void __user *unsafe_ptr__ign)
+{
+	return __bpf_dynptr_copy(dptr, off, size, (const void *)unsafe_ptr__ign,
+				 copy_user_data_nofault, NULL);
+}
+
+__bpf_kfunc int bpf_probe_read_kernel_dynptr(struct bpf_dynptr *dptr, u32 off,
+					     u32 size, const void *unsafe_ptr__ign)
+{
+	return __bpf_dynptr_copy(dptr, off, size, unsafe_ptr__ign,
+				 copy_kernel_data_nofault, NULL);
+}
+
+__bpf_kfunc int bpf_probe_read_user_str_dynptr(struct bpf_dynptr *dptr, u32 off,
+					       u32 size, const void __user *unsafe_ptr__ign)
+{
+	return __bpf_dynptr_copy_str(dptr, off, size, (const void *)unsafe_ptr__ign,
+				     copy_user_str_nofault, NULL);
+}
+
+__bpf_kfunc int bpf_probe_read_kernel_str_dynptr(struct bpf_dynptr *dptr, u32 off,
+						 u32 size, const void *unsafe_ptr__ign)
+{
+	return __bpf_dynptr_copy_str(dptr, off, size, unsafe_ptr__ign,
+				     copy_kernel_str_nofault, NULL);
+}
+
+__bpf_kfunc int bpf_copy_from_user_dynptr(struct bpf_dynptr *dptr, u32 off,
+					  u32 size, const void __user *unsafe_ptr__ign)
+{
+	return __bpf_dynptr_copy(dptr, off, size, (const void *)unsafe_ptr__ign,
+				 copy_user_data_sleepable, NULL);
+}
+
+__bpf_kfunc int bpf_copy_from_user_str_dynptr(struct bpf_dynptr *dptr, u32 off,
+					      u32 size, const void __user *unsafe_ptr__ign)
+{
+	return __bpf_dynptr_copy_str(dptr, off, size, (const void *)unsafe_ptr__ign,
+				     copy_user_str_sleepable, NULL);
+}
+
+__bpf_kfunc int bpf_copy_from_user_task_dynptr(struct bpf_dynptr *dptr, u32 off,
+					       u32 size, const void __user *unsafe_ptr__ign,
+					       struct task_struct *tsk)
+{
+	return __bpf_dynptr_copy(dptr, off, size, (const void *)unsafe_ptr__ign,
+				 copy_user_data_sleepable, tsk);
+}
+
+__bpf_kfunc int bpf_copy_from_user_task_str_dynptr(struct bpf_dynptr *dptr, u32 off,
+						   u32 size, const void __user *unsafe_ptr__ign,
+						   struct task_struct *tsk)
+{
+	return __bpf_dynptr_copy_str(dptr, off, size, (const void *)unsafe_ptr__ign,
+				     copy_user_str_sleepable, tsk);
+}
+
 __bpf_kfunc_end_defs();