Re: [PATCH v4 seccomp 5/5] seccomp/cache: Report cache data through /proc/pid/seccomp_cache

[Kees Cook]

On Fri, Oct 09, 2020 at 12:14:33PM -0500, YiFei Zhu wrote:
> From: YiFei Zhu <yifeifz2@xxxxxxxxxxxx>
> 
> Currently the kernel does not provide an infrastructure to translate
> architecture numbers to a human-readable name. Translating syscall
> numbers to syscall names is possible through FTRACE_SYSCALL
> infrastructure but it does not provide support for compat syscalls.
> 
> This will create a file for each PID as /proc/pid/seccomp_cache.
> The file will be empty when no seccomp filters are loaded, or be
> in the format of:
> <arch name> <decimal syscall number> <ALLOW | FILTER>
> where ALLOW means the cache is guaranteed to allow the syscall,
> and filter means the cache will pass the syscall to the BPF filter.
> 
> For the docker default profile on x86_64 it looks like:
> x86_64 0 ALLOW
> x86_64 1 ALLOW
> x86_64 2 ALLOW
> x86_64 3 ALLOW
> [...]
> x86_64 132 ALLOW
> x86_64 133 ALLOW
> x86_64 134 FILTER
> x86_64 135 FILTER
> x86_64 136 FILTER
> x86_64 137 ALLOW
> x86_64 138 ALLOW
> x86_64 139 FILTER
> x86_64 140 ALLOW
> x86_64 141 ALLOW
> [...]
> 
> This file is guarded by CONFIG_SECCOMP_CACHE_DEBUG with a default
> of N because I think certain users of seccomp might not want the
> application to know which syscalls are definitely usable. For
> the same reason, it is also guarded by CAP_SYS_ADMIN.
> 
> Suggested-by: Jann Horn <jannh@xxxxxxxxxx>
> Link: https://lore.kernel.org/lkml/CAG48ez3Ofqp4crXGksLmZY6=fGrF_tWyUCg7PBkAetvbbOPeOA@xxxxxxxxxxxxxx/
> Signed-off-by: YiFei Zhu <yifeifz2@xxxxxxxxxxxx>
> ---
>  arch/Kconfig                   | 24 ++++++++++++++
>  arch/x86/Kconfig               |  1 +
>  arch/x86/include/asm/seccomp.h |  3 ++
>  fs/proc/base.c                 |  6 ++++
>  include/linux/seccomp.h        |  5 +++
>  kernel/seccomp.c               | 59 ++++++++++++++++++++++++++++++++++
>  6 files changed, 98 insertions(+)
> 
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 21a3675a7a3a..85239a974f04 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -471,6 +471,15 @@ config HAVE_ARCH_SECCOMP_FILTER
>  	    results in the system call being skipped immediately.
>  	  - seccomp syscall wired up
>  
> +config HAVE_ARCH_SECCOMP_CACHE
> +	bool
> +	help
> +	  An arch should select this symbol if it provides all of these things:
> +	  - all the requirements for HAVE_ARCH_SECCOMP_FILTER
> +	  - SECCOMP_ARCH_NATIVE
> +	  - SECCOMP_ARCH_NATIVE_NR
> +	  - SECCOMP_ARCH_NATIVE_NAME
> +
> [...]
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 1ab22869a765..1a807f89ac77 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -150,6 +150,7 @@ config X86
>  	select HAVE_ARCH_COMPAT_MMAP_BASES	if MMU && COMPAT
>  	select HAVE_ARCH_PREL32_RELOCATIONS
>  	select HAVE_ARCH_SECCOMP_FILTER
> +	select HAVE_ARCH_SECCOMP_CACHE
>  	select HAVE_ARCH_THREAD_STRUCT_WHITELIST
>  	select HAVE_ARCH_STACKLEAK
>  	select HAVE_ARCH_TRACEHOOK

HAVE_ARCH_SECCOMP_CACHE isn't used any more. I think this was left over
from before.

-- 
Kees Cook