bpf: Mark PTR_TO_FUNC register initially with zero offset

mainline inclusion
from mainline-v5.17-rc1
commit d400a6cf
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I4WT90
CVE: CVE-2021-4204

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d400a6cf1c8a57cdf10f35220ead3284320d85ff



--------------------------------

Similar as with other pointer types where we use ldimm64, clear the register
content to zero first, and then populate the PTR_TO_FUNC type and subprogno
number. Currently this is not done, and leads to reuse of stale register
tracking data.

Given for special ldimm64 cases we always clear the register offset, make it
common for all cases, so it won't be forgotten in future.

Fixes: 69c087ba ("bpf: Add bpf_for_each_map_elem() helper")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Pu Lehui <pulehui@huawei.com>
Reviewed-by: Kuohai Xu <xukuohai@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>