selftests/bpf: Add verifier test for PTR_TO_MEM spill

mainline inclusion
from mainline-v5.11-rc5
commit 4237e9f4
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=4237e9f4a96228ccc8a7abe5e4b30834323cd353



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Add a test to check that the verifier is able to recognize spilling of
PTR_TO_MEM registers, by reserving a ringbuf buffer, forcing the spill
of a pointer holding the buffer address to the stack, filling it back
in from the stack and writing to the memory area pointed by it.

The patch was partially contributed by CyberArk Software, Inc.

Signed-off-by: Gilad Reti <gilad.reti@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Acked-by: KP Singh <kpsingh@kernel.org>
Link: https://lore.kernel.org/bpf/20210113053810.13518-2-gilad.reti@gmail.com


Signed-off-by: Pu Lehui <pulehui@huawei.com>
Reviewed-by: Kuohai Xu <xukuohai@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>