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Translating a context struct to string can be quite slow, especially if
the context has a lot of category bits set. This can cause quite
noticeable performance impact in situations where the translation needs
to be done repeatedly. A common example is a UNIX datagram socket with
the SO_PASSSEC option enabled, which is used e.g. by systemd-journald
when receiving log messages via datagram socket. This scenario can be
reproduced with:
cat /dev/urandom | base64 | logger &
timeout 30s perf record -p $(pidof systemd-journald) -a -g
kill %1
perf report -g none --pretty raw | grep security_secid_to_secctx
Before the caching introduced by this patch, computing the context
string (security_secid_to_secctx() function) takes up ~65% of
systemd-journald's CPU time (assuming a context with 1024 categories
set and Fedora x86_64 release kernel configs). After this patch
(assuming near-perfect cache hit ratio) this overhead is reduced to just
~2%.
This patch addresses the issue by caching a certain number (compile-time
configurable) of recently used context strings to speed up repeated
translations of the same context, while using only a small amount of
memory.
The cache is integrated into the existing sidtab table by adding a field
to each entry, which when not NULL contains an RCU-protected pointer to
a cache entry containing the cached string. The cache entries are kept
in a linked list sorted according to how recently they were used. On a
cache miss when the cache is full, the least recently used entry is
removed to make space for the new entry.
The patch migrates security_sid_to_context_core() to use the cache (also
a few other functions where it was possible without too much fuss, but
these mostly use the translation for logging in case of error, which is
rare).
Link: https://bugzilla.redhat.com/show_bug.cgi?id=1733259
Cc: Michal Sekletar <msekleta@redhat.com>
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Reviewed-by: Stephen Smalley <sds@tycho.nsa.gov>
Tested-by: Stephen Smalley <sds@tycho.nsa.gov>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
[PM: lots of merge fixups due to collisions with other sidtab patches]
Signed-off-by: Paul Moore <paul@paul-moore.com>
111 lines
4.3 KiB
Plaintext
111 lines
4.3 KiB
Plaintext
# SPDX-License-Identifier: GPL-2.0-only
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config SECURITY_SELINUX
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bool "NSA SELinux Support"
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depends on SECURITY_NETWORK && AUDIT && NET && INET
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select NETWORK_SECMARK
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default n
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help
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This selects NSA Security-Enhanced Linux (SELinux).
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You will also need a policy configuration and a labeled filesystem.
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If you are unsure how to answer this question, answer N.
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config SECURITY_SELINUX_BOOTPARAM
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bool "NSA SELinux boot parameter"
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depends on SECURITY_SELINUX
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default n
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help
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This option adds a kernel parameter 'selinux', which allows SELinux
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to be disabled at boot. If this option is selected, SELinux
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functionality can be disabled with selinux=0 on the kernel
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command line. The purpose of this option is to allow a single
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kernel image to be distributed with SELinux built in, but not
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necessarily enabled.
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If you are unsure how to answer this question, answer N.
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config SECURITY_SELINUX_DISABLE
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bool "NSA SELinux runtime disable"
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depends on SECURITY_SELINUX
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select SECURITY_WRITABLE_HOOKS
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default n
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help
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This option enables writing to a selinuxfs node 'disable', which
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allows SELinux to be disabled at runtime prior to the policy load.
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SELinux will then remain disabled until the next boot.
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This option is similar to the selinux=0 boot parameter, but is to
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support runtime disabling of SELinux, e.g. from /sbin/init, for
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portability across platforms where boot parameters are difficult
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to employ.
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NOTE: selecting this option will disable the '__ro_after_init'
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kernel hardening feature for security hooks. Please consider
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using the selinux=0 boot parameter instead of enabling this
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option.
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If you are unsure how to answer this question, answer N.
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config SECURITY_SELINUX_DEVELOP
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bool "NSA SELinux Development Support"
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depends on SECURITY_SELINUX
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default y
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help
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This enables the development support option of NSA SELinux,
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which is useful for experimenting with SELinux and developing
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policies. If unsure, say Y. With this option enabled, the
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kernel will start in permissive mode (log everything, deny nothing)
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unless you specify enforcing=1 on the kernel command line. You
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can interactively toggle the kernel between enforcing mode and
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permissive mode (if permitted by the policy) via /selinux/enforce.
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config SECURITY_SELINUX_AVC_STATS
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bool "NSA SELinux AVC Statistics"
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depends on SECURITY_SELINUX
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default y
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help
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This option collects access vector cache statistics to
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/selinux/avc/cache_stats, which may be monitored via
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tools such as avcstat.
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config SECURITY_SELINUX_CHECKREQPROT_VALUE
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int "NSA SELinux checkreqprot default value"
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depends on SECURITY_SELINUX
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range 0 1
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default 0
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help
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This option sets the default value for the 'checkreqprot' flag
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that determines whether SELinux checks the protection requested
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by the application or the protection that will be applied by the
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kernel (including any implied execute for read-implies-exec) for
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mmap and mprotect calls. If this option is set to 0 (zero),
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SELinux will default to checking the protection that will be applied
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by the kernel. If this option is set to 1 (one), SELinux will
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default to checking the protection requested by the application.
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The checkreqprot flag may be changed from the default via the
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'checkreqprot=' boot parameter. It may also be changed at runtime
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via /selinux/checkreqprot if authorized by policy.
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If you are unsure how to answer this question, answer 0.
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config SECURITY_SELINUX_SIDTAB_HASH_BITS
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int "NSA SELinux sidtab hashtable size"
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depends on SECURITY_SELINUX
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range 8 13
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default 9
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help
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This option sets the number of buckets used in the sidtab hashtable
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to 2^SECURITY_SELINUX_SIDTAB_HASH_BITS buckets. The number of hash
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collisions may be viewed at /sys/fs/selinux/ss/sidtab_hash_stats. If
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chain lengths are high (e.g. > 20) then selecting a higher value here
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will ensure that lookups times are short and stable.
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config SECURITY_SELINUX_SID2STR_CACHE_SIZE
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int "NSA SELinux SID to context string translation cache size"
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depends on SECURITY_SELINUX
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default 256
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help
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This option defines the size of the internal SID -> context string
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cache, which improves the performance of context to string
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conversion. Setting this option to 0 disables the cache completely.
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If unsure, keep the default value.
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