In the Linux kernel, the following vulnerability has been resolved:
bpf: Fix vmlinux BTF prep race in bpf_get_btf_vmlinux
bpf_get_btf_vmlinux() lazily parses the vmlinux BTF under the
bpf_verifier_lock, but publishes the result through a plain store
and re-checks it through a plain lockless load. Nothing orders
the stores initializing the struct btf inside btf_parse_vmlinux()
against the store publishing the pointer: On a weakly ordered
arch, a concurrent first-time caller taking the lockless fast
path could in principle observe the pointer before the parsed
contents are visible. The mutex_unlock() does not help such a
reader given it only synchronizes with a later acquisition of the
same lock. Thus, publish the pointer with smp_store_release()
and read it on the fast path with smp_load_acquire().
Acquire semantics are needed rather than a dependency-ordered
READ_ONCE(): btf_parse_vmlinux() also populates globals outside
the returned object (e.g. bpf_ctx_convert.t). An address
dependency would only order accesses performed through the
pointer and not cover other globals.
