[bpf-next,v2,2/7] bpf: Implement bpf_probe_read_user_dynptr helper

Commit Message

Levi Zim via B4 Relay Jan. 25, 2025, 8:29 a.m. UTC

From: Levi Zim <[e-mail]>

This patch add a helper function bpf_probe_read_user_dynptr:

long bpf_probe_read_user_dynptr(const struct bpf_dynptr *dst,
	u32 offset, u32 size, const void *unsafe_ptr, u64 flags);

It is useful for reading variable-length data from user memory into
dynptr.

Signed-off-by: Levi Zim <[e-mail]>
---
 include/uapi/linux/bpf.h | 16 ++++++++++
 kernel/bpf/helpers.c     |  3 ++
 kernel/trace/bpf_trace.c | 76 +++++++++++++++++++++++++++++++++---------------
 3 files changed, 71 insertions(+), 24 deletions(-)

Patch

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 2e08a59527ecf56732ea14ac34446b5eb25b5690..d7d7a9ddd5dca07ba89d81ba77101a704af3163b 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -5820,6 +5820,21 @@  union bpf_attr {
  *		support this helper, or if *flags* is not 0.
  *
  *		Or other negative errors on failure reading kernel memory.
+ *
+ * long bpf_probe_read_user_dynptr(const struct bpf_dynptr *dst, u32 offset, u32 size, const void *unsafe_ptr, u64 flags)
+ *	Description
+ *		Safely attempt to read *size* bytes from user space address
+ *		*unsafe_ptr* and store the data in *dst* starting from *offset*.
+ *		*flags* is currently unused.
+ *	Return
+ *		0 on success.
+ *
+ *		**-E2BIG** if *offset* + *len* exceeds the length of *src*'s data
+ *
+ *		**-EINVAL** if *src* is an invalid dynptr or doesn't support this
+ *		support this helper, or if *flags* is not 0.
+ *
+ *		Or other negative errors on failure reading user space memory.
  */
 #define ___BPF_FUNC_MAPPER(FN, ctx...)			\
 	FN(unspec, 0, ##ctx)				\
@@ -6035,6 +6050,7 @@  union bpf_attr {
 	FN(cgrp_storage_get, 210, ##ctx)		\
 	FN(cgrp_storage_delete, 211, ##ctx)		\
 	FN(probe_read_kernel_dynptr, 212, ##ctx)		\
+	FN(probe_read_user_dynptr, 213, ##ctx)		\
 	/* */
 
 /* backwards-compatibility macros for users of __BPF_FUNC_MAPPER that don't
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index a736dc9e7be98571103ba404420be0da4dac4fbe..ac563d09082e7c721999d7de035aabc000206a29 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -1898,6 +1898,7 @@  const struct bpf_func_proto bpf_get_current_task_proto __weak;
 const struct bpf_func_proto bpf_get_current_task_btf_proto __weak;
 const struct bpf_func_proto bpf_probe_read_user_proto __weak;
 const struct bpf_func_proto bpf_probe_read_user_str_proto __weak;
+const struct bpf_func_proto bpf_probe_read_user_dynptr_proto __weak;
 const struct bpf_func_proto bpf_probe_read_kernel_proto __weak;
 const struct bpf_func_proto bpf_probe_read_kernel_str_proto __weak;
 const struct bpf_func_proto bpf_probe_read_kernel_dynptr_proto __weak;
@@ -2029,6 +2030,8 @@  bpf_base_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_get_current_task_btf_proto;
 	case BPF_FUNC_probe_read_user:
 		return &bpf_probe_read_user_proto;
+	case BPF_FUNC_probe_read_user_dynptr:
+		return &bpf_probe_read_user_dynptr_proto;
 	case BPF_FUNC_probe_read_kernel:
 		return security_locked_down(LOCKDOWN_BPF_READ_KERNEL) < 0 ?
 		       NULL : &bpf_probe_read_kernel_proto;
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 75c9d1e8d04c3b8930ae81345f5586756ce8b5ec..d9f704c1342773c74b2414be4adfc8271d6d364d 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -181,6 +181,36 @@  bpf_probe_read_user_common(void *dst, u32 size, const void __user *unsafe_ptr)
 	return ret;
 }
 
+static int bpf_probe_read_check_dynptr(const struct bpf_dynptr_kern *dst,
+	u32 offset, u32 size, u64 flags)
+{
+	enum bpf_dynptr_type type;
+	int err;
+
+	if (!dst->data || __bpf_dynptr_is_rdonly(dst))
+		return -EINVAL;
+
+	err = bpf_dynptr_check_off_len(dst, offset, size);
+	if (err)
+		return err;
+
+	type = bpf_dynptr_get_type(dst);
+
+	switch (type) {
+	case BPF_DYNPTR_TYPE_LOCAL:
+	case BPF_DYNPTR_TYPE_RINGBUF:
+		if (flags)
+			return -EINVAL;
+		return 0;
+	case BPF_DYNPTR_TYPE_SKB:
+	case BPF_DYNPTR_TYPE_XDP:
+		return -EINVAL;
+	default:
+		WARN_ONCE(true, "%s: unknown dynptr type %d\n", __func__, type);
+		return -EFAULT;
+	}
+}
+
 BPF_CALL_3(bpf_probe_read_user, void *, dst, u32, size,
 	   const void __user *, unsafe_ptr)
 {
@@ -196,6 +226,26 @@  const struct bpf_func_proto bpf_probe_read_user_proto = {
 	.arg3_type	= ARG_ANYTHING,
 };
 
+BPF_CALL_5(bpf_probe_read_user_dynptr, const struct bpf_dynptr_kern *, dst,
+	u32, offset, u32, size, void *, unsafe_ptr, u64, flags)
+{
+	int ret = bpf_probe_read_check_dynptr(dst, offset, size, flags);
+
+	return ret ?: bpf_probe_read_user_common(dst->data + dst->offset + offset,
+				size, unsafe_ptr);
+}
+
+const struct bpf_func_proto bpf_probe_read_user_dynptr_proto = {
+	.func		= bpf_probe_read_user_dynptr,
+	.gpl_only	= true,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_DYNPTR | MEM_RDONLY,
+	.arg2_type	= ARG_ANYTHING,
+	.arg3_type	= ARG_ANYTHING,
+	.arg4_type	= ARG_ANYTHING,
+	.arg5_type	= ARG_ANYTHING,
+};
+
 static __always_inline int
 bpf_probe_read_user_str_common(void *dst, u32 size,
 			       const void __user *unsafe_ptr)
@@ -251,32 +301,10 @@  const struct bpf_func_proto bpf_probe_read_kernel_proto = {
 BPF_CALL_5(bpf_probe_read_kernel_dynptr, const struct bpf_dynptr_kern *, dst,
 	u32, offset, u32, size, void *, unsafe_ptr, u64, flags)
 {
-	enum bpf_dynptr_type type;
-	int err;
-
-	if (!dst->data || __bpf_dynptr_is_rdonly(dst))
-		return -EINVAL;
+	int ret = bpf_probe_read_check_dynptr(dst, offset, size, flags);
 
-	err = bpf_dynptr_check_off_len(dst, offset, size);
-	if (err)
-		return err;
-
-	type = bpf_dynptr_get_type(dst);
-
-	switch (type) {
-	case BPF_DYNPTR_TYPE_LOCAL:
-	case BPF_DYNPTR_TYPE_RINGBUF:
-		if (flags)
-			return -EINVAL;
-		return bpf_probe_read_kernel_common(dst->data + dst->offset + offset,
+	return ret ?: bpf_probe_read_kernel_common(dst->data + dst->offset + offset,
 				size, unsafe_ptr);
-	case BPF_DYNPTR_TYPE_SKB:
-	case BPF_DYNPTR_TYPE_XDP:
-		return -EINVAL;
-	default:
-		WARN_ONCE(true, "%s: unknown dynptr type %d\n", __func__, type);
-		return -EFAULT;
-	}
 }
 
 const struct bpf_func_proto bpf_probe_read_kernel_dynptr_proto = {