bpf: Add flags arg to bpf_dynptr_read and bpf_dynptr_write APIs

Commit 13bbbfbe ("bpf: Add bpf_dynptr_read and bpf_dynptr_write")
added the bpf_dynptr_write() and bpf_dynptr_read() APIs.

However, it will be needed for some dynptr types to pass in flags as
well (e.g. when writing to a skb, the user may like to invalidate the
hash or recompute the checksum).

This patch adds a "u64 flags" arg to the bpf_dynptr_read() and
bpf_dynptr_write() APIs before their UAPI signature freezes where
we then cannot change them anymore with a 5.19.x released kernel.

Fixes: 13bbbfbe ("bpf: Add bpf_dynptr_read and bpf_dynptr_write")
Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/r/20220706232547.4016651-1-joannelkoong@gmail.com

include/uapi/linux/bpf.h

@@ -5222,22 +5222,25 @@ union bpf_attr {
  *	Return
  *		Nothing. Always succeeds.
  *
- * long bpf_dynptr_read(void *dst, u32 len, struct bpf_dynptr *src, u32 offset)
+ * long bpf_dynptr_read(void *dst, u32 len, struct bpf_dynptr *src, u32 offset, u64 flags)
  *	Description
  *		Read *len* bytes from *src* into *dst*, starting from *offset*
  *		into *src*.
+ *		*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.
+ *		of *src*'s data, -EINVAL if *src* is an invalid dynptr or if
+ *		*flags* is not 0.
  *
- * long bpf_dynptr_write(struct bpf_dynptr *dst, u32 offset, void *src, u32 len)
+ * long bpf_dynptr_write(struct bpf_dynptr *dst, u32 offset, void *src, u32 len, u64 flags)
  *	Description
  *		Write *len* bytes from *src* into *dst*, starting from *offset*
  *		into *dst*.
+ *		*flags* is currently unused.
  *	Return
  *		0 on success, -E2BIG if *offset* + *len* exceeds the length
  *		of *dst*'s data, -EINVAL if *dst* is an invalid dynptr or if *dst*
- *		is a read-only dynptr.
+ *		is a read-only dynptr or if *flags* is not 0.
  *
  * void *bpf_dynptr_data(struct bpf_dynptr *ptr, u32 offset, u32 len)
  *	Description

kernel/bpf/helpers.c

@@ -1497,11 +1497,12 @@ const struct bpf_func_proto bpf_dynptr_from_mem_proto = {
 	.arg4_type	= ARG_PTR_TO_DYNPTR | DYNPTR_TYPE_LOCAL | MEM_UNINIT,
 };
 
-BPF_CALL_4(bpf_dynptr_read, void *, dst, u32, len, struct bpf_dynptr_kern *, src, u32, offset)
+BPF_CALL_5(bpf_dynptr_read, void *, dst, u32, len, struct bpf_dynptr_kern *, src,
+	   u32, offset, u64, flags)
 {
 	int err;
 
-	if (!src->data)
+	if (!src->data || flags)
 		return -EINVAL;
 
 	err = bpf_dynptr_check_off_len(src, offset, len);
@@ -1521,13 +1522,15 @@ const struct bpf_func_proto bpf_dynptr_read_proto = {
 	.arg2_type	= ARG_CONST_SIZE_OR_ZERO,
 	.arg3_type	= ARG_PTR_TO_DYNPTR,
 	.arg4_type	= ARG_ANYTHING,
+	.arg5_type	= ARG_ANYTHING,
 };
 
-BPF_CALL_4(bpf_dynptr_write, struct bpf_dynptr_kern *, dst, u32, offset, void *, src, u32, len)
+BPF_CALL_5(bpf_dynptr_write, struct bpf_dynptr_kern *, dst, u32, offset, void *, src,
+	   u32, len, u64, flags)
 {
 	int err;
 
-	if (!dst->data || bpf_dynptr_is_rdonly(dst))
+	if (!dst->data || flags || bpf_dynptr_is_rdonly(dst))
 		return -EINVAL;
 
 	err = bpf_dynptr_check_off_len(dst, offset, len);
@@ -1547,6 +1550,7 @@ const struct bpf_func_proto bpf_dynptr_write_proto = {
 	.arg2_type	= ARG_ANYTHING,
 	.arg3_type	= ARG_PTR_TO_MEM | MEM_RDONLY,
 	.arg4_type	= ARG_CONST_SIZE_OR_ZERO,
+	.arg5_type	= ARG_ANYTHING,
 };
 
 BPF_CALL_3(bpf_dynptr_data, struct bpf_dynptr_kern *, ptr, u32, offset, u32, len)

tools/include/uapi/linux/bpf.h

@@ -5222,22 +5222,25 @@ union bpf_attr {
  *	Return
  *		Nothing. Always succeeds.
  *
- * long bpf_dynptr_read(void *dst, u32 len, struct bpf_dynptr *src, u32 offset)
+ * long bpf_dynptr_read(void *dst, u32 len, struct bpf_dynptr *src, u32 offset, u64 flags)
  *	Description
  *		Read *len* bytes from *src* into *dst*, starting from *offset*
  *		into *src*.
+ *		*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.
+ *		of *src*'s data, -EINVAL if *src* is an invalid dynptr or if
+ *		*flags* is not 0.
  *
- * long bpf_dynptr_write(struct bpf_dynptr *dst, u32 offset, void *src, u32 len)
+ * long bpf_dynptr_write(struct bpf_dynptr *dst, u32 offset, void *src, u32 len, u64 flags)
  *	Description
  *		Write *len* bytes from *src* into *dst*, starting from *offset*
  *		into *dst*.
+ *		*flags* is currently unused.
  *	Return
  *		0 on success, -E2BIG if *offset* + *len* exceeds the length
  *		of *dst*'s data, -EINVAL if *dst* is an invalid dynptr or if *dst*
- *		is a read-only dynptr.
+ *		is a read-only dynptr or if *flags* is not 0.
  *
  * void *bpf_dynptr_data(struct bpf_dynptr *ptr, u32 offset, u32 len)
  *	Description

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

@@ -140,12 +140,12 @@ int use_after_invalid(void *ctx)
 
 	bpf_ringbuf_reserve_dynptr(&ringbuf, sizeof(read_data), 0, &ptr);
 
-	bpf_dynptr_read(read_data, sizeof(read_data), &ptr, 0);
+	bpf_dynptr_read(read_data, sizeof(read_data), &ptr, 0, 0);
 
 	bpf_ringbuf_submit_dynptr(&ptr, 0);
 
 	/* this should fail */
-	bpf_dynptr_read(read_data, sizeof(read_data), &ptr, 0);
+	bpf_dynptr_read(read_data, sizeof(read_data), &ptr, 0, 0);
 
 	return 0;
 }
@@ -338,7 +338,7 @@ int invalid_helper2(void *ctx)
 	get_map_val_dynptr(&ptr);
 
 	/* this should fail */
-	bpf_dynptr_read(read_data, sizeof(read_data), (void *)&ptr + 8, 0);
+	bpf_dynptr_read(read_data, sizeof(read_data), (void *)&ptr + 8, 0, 0);
 
 	return 0;
 }
@@ -377,7 +377,7 @@ int invalid_write2(void *ctx)
 	memcpy((void *)&ptr + 8, &x, sizeof(x));
 
 	/* this should fail */
-	bpf_dynptr_read(read_data, sizeof(read_data), &ptr, 0);
+	bpf_dynptr_read(read_data, sizeof(read_data), &ptr, 0, 0);
 
 	bpf_ringbuf_submit_dynptr(&ptr, 0);
 
@@ -473,7 +473,7 @@ int invalid_read2(void *ctx)
 	get_map_val_dynptr(&ptr);
 
 	/* this should fail */
-	bpf_dynptr_read(read_data, sizeof(read_data), (void *)&ptr + 1, 0);
+	bpf_dynptr_read(read_data, sizeof(read_data), (void *)&ptr + 1, 0, 0);
 
 	return 0;
 }

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

@@ -43,10 +43,10 @@ int test_read_write(void *ctx)
 	bpf_ringbuf_reserve_dynptr(&ringbuf, sizeof(write_data), 0, &ptr);
 
 	/* Write data into the dynptr */
-	err = err ?: bpf_dynptr_write(&ptr, 0, write_data, sizeof(write_data));
+	err = bpf_dynptr_write(&ptr, 0, write_data, sizeof(write_data), 0);
 
 	/* Read the data that was written into the dynptr */
-	err = err ?: bpf_dynptr_read(read_data, sizeof(read_data), &ptr, 0);
+	err = err ?: bpf_dynptr_read(read_data, sizeof(read_data), &ptr, 0, 0);
 
 	/* Ensure the data we read matches the data we wrote */
 	for (i = 0; i < sizeof(read_data); i++) {