From 5fc5d8fded57e5de0c0b56b00c4cfc522aa8c572 Mon Sep 17 00:00:00 2001 From: Ihor Solodrai Date: Wed, 2 Jul 2025 14:03:08 -0700 Subject: [PATCH] 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: Ihor Solodrai Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20250702210309.3115903-2-isolodrai@meta.com --- kernel/bpf/helpers.c | 47 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 47 insertions(+) diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index f48fa3fe8decf..5269381d6d3d3 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -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 -- 2.47.2