GDB 无法attach进程

gdb attach fails with ptrace: Operation not permitted
Today I ran into a weird problem. I could not attach to my own process with gdb. The process ran under my UID, but gdb refused to attach. This is a problem of wrong permissions, although /proc/[pid]/status looked ok:

Uid:    1000    1000    1000    1000
Gid:    1000    1000    1000    1000

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Uid:    1000    1000    1000    1000
Gid:    1000    1000    1000    1000

I am the owner but cannot attach? Well, I launched gdb as root and could attach. Strange. Without digging deeper into this, my dirty workaround was this:

sudo chmod +s /usr/bin/gdb
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sudo chmod +s /usr/bin/gdb

Update: Thanks to Mario, who pointed out, that the reason is the Kernel hardening stuff build into the Ubuntu kernel. See his comment how to fix the problem permanently.

why i cannot get a really address for
#

#0  0xf76f9c89 in __kernel_vsyscall ()
#1  0xf75fbb13 in __read_nocancel () at ../sysdeps/unix/syscall-template.S:84
#2  0x080484df in vulnerable_function ()
#3  0x0804851d in main ()
#4  0xf753e637 in __libc_start_main (main=0x804850a <main>, argc=0x1, 
argv=0xffde0464, init=0x8048540 <__libc_csu_init>, 
fini=0x80485b0 <__libc_csu_fini>, rtld_fini=0xf770a8a0 <_dl_fini>, 
stack_end=0xffde045c) at ../csu/libc-start.c:291
#5  0x08048411 in _start ()
#