Commit 5fc5d8fd authored by Ihor Solodrai's avatar Ihor Solodrai Committed by Andrii Nakryiko
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bpf: Add bpf_dynptr_memset() kfunc 



Currently there is no straightforward way to fill dynptr memory with a
value (most commonly zero). One can do it with bpf_dynptr_write(), but
a temporary buffer is necessary for that.

Implement bpf_dynptr_memset() - an analogue of memset() from libc.

Signed-off-by: default avatarIhor Solodrai <isolodrai@meta.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20250702210309.3115903-2-isolodrai@meta.com
parent 38d95beb

kernel/bpf/helpers.c

+47 −0
Original line number Diff line number Diff line
@@ -2907,6 +2907,52 @@ __bpf_kfunc int bpf_dynptr_copy(struct bpf_dynptr *dst_ptr, u32 dst_off, 
	return 0;

}



/**

 * bpf_dynptr_memset() - Fill dynptr memory with a constant byte.

 * @p: Destination dynptr - where data will be filled

 * @offset: Offset into the dynptr to start filling from

 * @size: Number of bytes to fill

 * @val: Constant byte to fill the memory with

 *

 * Fills the @size bytes of the memory area pointed to by @p

 * at @offset with the constant byte @val.

 * Returns 0 on success; negative error, otherwise.

 */

 __bpf_kfunc int bpf_dynptr_memset(struct bpf_dynptr *p, u32 offset, u32 size, u8 val)

 {

	struct bpf_dynptr_kern *ptr = (struct bpf_dynptr_kern *)p;

	u32 chunk_sz, write_off;

	char buf[256];

	void* slice;

	int err;



	slice = bpf_dynptr_slice_rdwr(p, offset, NULL, size);

	if (likely(slice)) {

		memset(slice, val, size);

		return 0;

	}



	if (__bpf_dynptr_is_rdonly(ptr))

		return -EINVAL;



	err = bpf_dynptr_check_off_len(ptr, offset, size);

	if (err)

		return err;



	/* Non-linear data under the dynptr, write from a local buffer */

	chunk_sz = min_t(u32, sizeof(buf), size);

	memset(buf, val, chunk_sz);



	for (write_off = 0; write_off < size; write_off += chunk_sz) {

		chunk_sz = min_t(u32, sizeof(buf), size - write_off);

		err = __bpf_dynptr_write(ptr, offset + write_off, buf, chunk_sz, 0);

		if (err)

			return err;

	}



	return 0;

}



__bpf_kfunc void *bpf_cast_to_kern_ctx(void *obj)

{

	return obj;
@@ -3735,6 +3781,7 @@ 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)

BTF_ID_FLAGS(func, bpf_dynptr_memset)

#ifdef CONFIG_NET

BTF_ID_FLAGS(func, bpf_modify_return_test_tp)

#endif