From: Kees Cook <keescook@chromium.org>
To: KP Singh <kpsingh@kernel.org>
Cc: linux-security-module@vger.kernel.org, bpf@vger.kernel.org,
paul@paul-moore.com, casey@schaufler-ca.com, song@kernel.org,
daniel@iogearbox.net, ast@kernel.org, renauld@google.com
Subject: Re: [PATCH v5 5/5] security: Add CONFIG_SECURITY_HOOK_LIKELY
Date: Thu, 28 Sep 2023 17:38:01 -0700 [thread overview]
Message-ID: <202309281737.03A25A9@keescook> (raw)
In-Reply-To: <20230928202410.3765062-6-kpsingh@kernel.org>
On Thu, Sep 28, 2023 at 10:24:10PM +0200, KP Singh wrote:
> This config influences the nature of the static key that guards the
> static call for LSM hooks.
>
> When enabled, it indicates that an LSM static call slot is more likely
> to be initialized. When disabled, it optimizes for the case when static
> call slot is more likely to be not initialized.
>
> When a major LSM like (SELinux, AppArmor, Smack etc) is active on a
> system the system would benefit from enabling the config. However there
> are other cases which would benefit from the config being disabled
> (e.g. a system with a BPF LSM with no hooks enabled by default, or an
> LSM like loadpin / yama). Ultimately, there is no one-size fits all
> solution.
>
> with CONFIG_SECURITY_HOOK_LIKELY enabled, the inactive /
> uninitialized case is penalized with a direct jmp (still better than
> an indirect jmp):
>
> function security_file_ioctl:
> 0xffffffff818f0c80 <+0>: endbr64
> 0xffffffff818f0c84 <+4>: nopl 0x0(%rax,%rax,1)
> 0xffffffff818f0c89 <+9>: push %rbp
> 0xffffffff818f0c8a <+10>: push %r14
> 0xffffffff818f0c8c <+12>: push %rbx
> 0xffffffff818f0c8d <+13>: mov %rdx,%rbx
> 0xffffffff818f0c90 <+16>: mov %esi,%ebp
> 0xffffffff818f0c92 <+18>: mov %rdi,%r14
> 0xffffffff818f0c95 <+21>: jmp 0xffffffff818f0ca8 <security_file_ioctl+40>
>
> jump to skip the inactive BPF LSM hook.
>
> 0xffffffff818f0c97 <+23>: mov %r14,%rdi
> 0xffffffff818f0c9a <+26>: mov %ebp,%esi
> 0xffffffff818f0c9c <+28>: mov %rbx,%rdx
> 0xffffffff818f0c9f <+31>: call 0xffffffff8141e3b0 <bpf_lsm_file_ioctl>
> 0xffffffff818f0ca4 <+36>: test %eax,%eax
> 0xffffffff818f0ca6 <+38>: jne 0xffffffff818f0cbf <security_file_ioctl+63>
> 0xffffffff818f0ca8 <+40>: endbr64
> 0xffffffff818f0cac <+44>: jmp 0xffffffff818f0ccd <security_file_ioctl+77>
>
> jump to skip the empty slot.
>
> 0xffffffff818f0cae <+46>: mov %r14,%rdi
> 0xffffffff818f0cb1 <+49>: mov %ebp,%esi
> 0xffffffff818f0cb3 <+51>: mov %rbx,%rdx
> 0xffffffff818f0cb6 <+54>: nopl 0x0(%rax,%rax,1)
> ^^^^^^^^^^^^^^^^^^^^^^^
> Empty slot
>
> 0xffffffff818f0cbb <+59>: test %eax,%eax
> 0xffffffff818f0cbd <+61>: je 0xffffffff818f0ccd <security_file_ioctl+77>
> 0xffffffff818f0cbf <+63>: endbr64
> 0xffffffff818f0cc3 <+67>: pop %rbx
> 0xffffffff818f0cc4 <+68>: pop %r14
> 0xffffffff818f0cc6 <+70>: pop %rbp
> 0xffffffff818f0cc7 <+71>: cs jmp 0xffffffff82c00000 <__x86_return_thunk>
> 0xffffffff818f0ccd <+77>: endbr64
> 0xffffffff818f0cd1 <+81>: xor %eax,%eax
> 0xffffffff818f0cd3 <+83>: jmp 0xffffffff818f0cbf <security_file_ioctl+63>
> 0xffffffff818f0cd5 <+85>: mov %r14,%rdi
> 0xffffffff818f0cd8 <+88>: mov %ebp,%esi
> 0xffffffff818f0cda <+90>: mov %rbx,%rdx
> 0xffffffff818f0cdd <+93>: pop %rbx
> 0xffffffff818f0cde <+94>: pop %r14
> 0xffffffff818f0ce0 <+96>: pop %rbp
> 0xffffffff818f0ce1 <+97>: ret
>
> When the config is disabled, the case optimizes the scenario above.
>
> security_file_ioctl:
> 0xffffffff818f0e30 <+0>: endbr64
> 0xffffffff818f0e34 <+4>: nopl 0x0(%rax,%rax,1)
> 0xffffffff818f0e39 <+9>: push %rbp
> 0xffffffff818f0e3a <+10>: push %r14
> 0xffffffff818f0e3c <+12>: push %rbx
> 0xffffffff818f0e3d <+13>: mov %rdx,%rbx
> 0xffffffff818f0e40 <+16>: mov %esi,%ebp
> 0xffffffff818f0e42 <+18>: mov %rdi,%r14
> 0xffffffff818f0e45 <+21>: xchg %ax,%ax
> 0xffffffff818f0e47 <+23>: xchg %ax,%ax
>
> The static keys in their disabled state do not create jumps leading
> to faster code.
>
> 0xffffffff818f0e49 <+25>: xor %eax,%eax
> 0xffffffff818f0e4b <+27>: xchg %ax,%ax
> 0xffffffff818f0e4d <+29>: pop %rbx
> 0xffffffff818f0e4e <+30>: pop %r14
> 0xffffffff818f0e50 <+32>: pop %rbp
> 0xffffffff818f0e51 <+33>: cs jmp 0xffffffff82c00000 <__x86_return_thunk>
> 0xffffffff818f0e57 <+39>: endbr64
> 0xffffffff818f0e5b <+43>: mov %r14,%rdi
> 0xffffffff818f0e5e <+46>: mov %ebp,%esi
> 0xffffffff818f0e60 <+48>: mov %rbx,%rdx
> 0xffffffff818f0e63 <+51>: call 0xffffffff8141e3b0 <bpf_lsm_file_ioctl>
> 0xffffffff818f0e68 <+56>: test %eax,%eax
> 0xffffffff818f0e6a <+58>: jne 0xffffffff818f0e4d <security_file_ioctl+29>
> 0xffffffff818f0e6c <+60>: jmp 0xffffffff818f0e47 <security_file_ioctl+23>
> 0xffffffff818f0e6e <+62>: endbr64
> 0xffffffff818f0e72 <+66>: mov %r14,%rdi
> 0xffffffff818f0e75 <+69>: mov %ebp,%esi
> 0xffffffff818f0e77 <+71>: mov %rbx,%rdx
> 0xffffffff818f0e7a <+74>: nopl 0x0(%rax,%rax,1)
> 0xffffffff818f0e7f <+79>: test %eax,%eax
> 0xffffffff818f0e81 <+81>: jne 0xffffffff818f0e4d <security_file_ioctl+29>
> 0xffffffff818f0e83 <+83>: jmp 0xffffffff818f0e49 <security_file_ioctl+25>
> 0xffffffff818f0e85 <+85>: endbr64
> 0xffffffff818f0e89 <+89>: mov %r14,%rdi
> 0xffffffff818f0e8c <+92>: mov %ebp,%esi
> 0xffffffff818f0e8e <+94>: mov %rbx,%rdx
> 0xffffffff818f0e91 <+97>: pop %rbx
> 0xffffffff818f0e92 <+98>: pop %r14
> 0xffffffff818f0e94 <+100>: pop %rbp
> 0xffffffff818f0e95 <+101>: ret
>
> Acked-by: Song Liu <song@kernel.org>
> Signed-off-by: KP Singh <kpsingh@kernel.org>
This looks excellent, and gives us the right balance automatically. :)
Reviewed-by: Kees Cook <keescook@chromium.org>
--
Kees Cook
next prev parent reply other threads:[~2023-09-29 0:38 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-28 20:24 [PATCH v5 0/5] Reduce overhead of LSMs with static calls KP Singh
2023-09-28 20:24 ` [PATCH v5 1/5] kernel: Add helper macros for loop unrolling KP Singh
2023-09-28 20:24 ` [PATCH v5 2/5] security: Count the LSMs enabled at compile time KP Singh
2023-09-29 0:37 ` Kees Cook
2023-09-28 20:24 ` [PATCH v5 3/5] security: Replace indirect LSM hook calls with static calls KP Singh
2023-09-30 16:13 ` kernel test robot
2023-09-30 20:40 ` Kees Cook
2023-10-04 0:09 ` KP Singh
2023-09-28 20:24 ` [PATCH v5 4/5] bpf: Only enable BPF LSM hooks when an LSM program is attached KP Singh
2023-10-05 8:09 ` Jiri Olsa
2023-10-05 13:26 ` KP Singh
2023-10-05 13:27 ` KP Singh
2023-10-05 13:52 ` Jiri Olsa
2023-10-05 16:07 ` KP Singh
2023-10-06 7:27 ` Jiri Olsa
2023-10-06 9:05 ` Jiri Olsa
2023-10-06 10:57 ` KP Singh
2023-10-06 18:32 ` KP Singh
2023-09-28 20:24 ` [PATCH v5 5/5] security: Add CONFIG_SECURITY_HOOK_LIKELY KP Singh
2023-09-29 0:38 ` Kees Cook [this message]
2023-09-29 0:41 ` [PATCH v5 0/5] Reduce overhead of LSMs with static calls Kees Cook
2023-10-02 11:06 ` Paolo Abeni
2023-10-02 11:09 ` KP Singh
2023-10-02 13:27 ` Paolo Abeni
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