selftest/bpf: Verifier tests for var-off access

stable inclusion
from stable-5.10.57
commit 7254e2d9eb416fdfd57473c7e1d6393cdb1321a1
bugzilla: 176179 https://gitee.com/openeuler/kernel/issues/I4DZ64

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7254e2d9eb416fdfd57473c7e1d6393cdb1321a1



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

commit 7a22930c upstream

Add tests for the new functionality - reading and writing to the stack
through a variable-offset pointer.

Signed-off-by: Andrei Matei <andreimatei1@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210207011027.676572-4-andreimatei1@gmail.com


Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Acked-by: Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>