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bpf: Add bpf_dynptr_memset() kfunc

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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: Ihor Solodrai <isolodrai@meta.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20250702210309.3115903-2-isolodrai@meta.com
This commit is contained in:
Ihor Solodrai 2025-07-02 14:03:08 -07:00 committed by Andrii Nakryiko
parent 38d95beb4b
commit 5fc5d8fded
1 changed files with 47 additions and 0 deletions
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47
kernel/bpf/helpers.c
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@ -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