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bpf: Add a kfunc to type cast from bpf uapi ctx to kernel ctx

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Implement bpf_cast_to_kern_ctx() kfunc which does a type cast
of a uapi ctx object to the corresponding kernel ctx. Previously
if users want to access some data available in kctx but not
in uapi ctx, bpf_probe_read_kernel() helper is needed.
The introduction of bpf_cast_to_kern_ctx() allows direct
memory access which makes code simpler and easier to understand.

Signed-off-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/r/20221120195432.3113982-1-yhs@fb.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Yonghong Song
2022-11-20 11:54:32 -08:00
committed by Alexei Starovoitov
parent cfe1456440
commit fd264ca020
4 changed files with 53 additions and 0 deletions
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6
kernel/bpf/helpers.c
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@@ -1879,6 +1879,11 @@ void bpf_task_release(struct task_struct *p)
put_task_struct_rcu_user(p);
}
void *bpf_cast_to_kern_ctx(void *obj)
{
return obj;
}
__diag_pop();
BTF_SET8_START(generic_btf_ids)
@@ -1907,6 +1912,7 @@ BTF_ID(struct, task_struct)
BTF_ID(func, bpf_task_release)
BTF_SET8_START(common_btf_ids)
BTF_ID_FLAGS(func, bpf_cast_to_kern_ctx)
BTF_SET8_END(common_btf_ids)
static const struct btf_kfunc_id_set common_kfunc_set = {