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Date: Sun, 10 May 2020 10:16:25 +0800
From: wzt wzt <>
Subject: Open source a new kernel harden project

    This is a new kernel harden project called hksp(huawei kernel self
protection),  hope some of the mitigation ideas may help you, thanks.

Huawei kernel self protection

Cred guard
- random cred's magic.
  most kernel exploit try to find some offsets in struct cred,
  but it depends on CONFIG_DEBUG_CREDENTIALS, then need to compute
  the right offset by that kernel config, so mostly the exploit code
  is something like that:
  if (tmp0 == 0x43736564 || tmp0 == 0x44656144)
        i += 4;
- detect shellcode like:
  the common kernel code is never write like that.

Namespace Guard
This feature detects pid namespace escape via kernel exploits.
The current public method to bypass namespace is hijack init_nsproxy
to current process:
  switch_task_namespaces_p(current, init_nsproxy_p);

Rop stack pivot
- user process stack can't be is mmap area.
- check kernel stack range at each system call ret.
  the rsp pointer can point below __PAGE_OFFSET.

Slub harden
- redzone/poison randomization.
- double free enhance.
  old slub can only detect continuous double free bugs.

  hksp can detect no continuous double/multi free bugs.


- clear the next object address information when using kmalloc function.

Proc info leak
Protect important file with no read access for non root user.
set /proc/{modules,keys,key-users},
/proc/sys/vm/{mmap_min_addr} as 0640.

Aslr hardended
User stack aslr enhanced.
Old user process's stack is between 0-1G on 64bit.
the actually random range is 0-2^24.
we introduce STACK_RND_BITS to control the range dynamically.

echo "24" > /proc/sys/vm/stack_rnd_bits

we also randomize the space between elf_info and environ.
And randomize the space between stack and elf_info.

Ptrace hardened
Disallow attach to non child process.
This can prevent process memory inject via ptrace.

Sm*p hardened
Check smap&smep when return from kernel space via a syscall,
this can detect some kernel exploit code to bypass smap & smep
feature via rop attack technology.

Raw socket enhance
Enhance raw socket for ipv4 protocol.
- TCP data cannot be sent over raw sockets.
  echo 1 > /proc/sys/net/ipv4/raw_tcp_disabled
- UDP datagrams with an invalid source address cannot be sent
  over raw sockets. The IP source address for any outgoing UDP
  datagram must exist on a network interface or the datagram is
  dropped. This change was made to limit the ability of malicious
  code to create distributed denial-of-service attacks and limits
  the ability to send spoofed packets (TCP/IP packets with a forged
  source IP address).
  echo 1 > /proc/sys/net/ipv4/raw_udp_verify
- A call to the bind function with a raw socket for the IPPROTO_TCP
  protocol is not allowed.
  echo 1 > /proc/sys/net/ipv4/raw_bind_disabled

Kernel self guard
Ksguard is an anti rootkit tool on kernel level.
Currently it can detect 4 types of kernel rootkits,
These are the most popluar rootkits type on unix world.

- keyboard notifer rootkits.
- netfilter hooks rootkits.
- tty sniffer rootkits and other DKOM(direct kernel object modify) rootkits.
- system call table hijack rootkits.

/sbin/insmod /lib/modules/5.6.7/kernel/security/ksguard/ksguard.ko

Detect keyboard notifer rootkits:
echo "1" > /proc/ksguard/state

Detect netfilter hooks rootkits:
echo "2" > /proc/ksguard/state

Detect tty sniffer rootkits:
echo "3" > /proc/ksguard/state

Detect syscall table pointer:
echo "4" > /proc/ksguard/state

Arbitrary code guard
we extended the libc personality() to support:
- mmap can't memory with PROT_WRITE|PROT_EXEC.
- mprtect can't change PROT_WRITE to PROT_EXEC.

Code integrity guard
To support certificate for user process execve.
it can prevent some internet explorer to load
third party so librarys.

Hide symbol
Hide symbols from /proc/kallsyms.

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