Some hardening options like HARDENED_USERCOPY can be set at boot time and have negligible cost when disabled. The default for options like init_on_alloc= can be set at compile time but hardened usercopy is enabled by default if built in. This incurs overhead when a kernel wishes to provide optional hardening but the user does not necessarily care.
Hardening is desirable in some environments but ideally they would be opt-in by kernel command line as hardening is typically a deliberate decision whereas the performance overhead is not always obvious to all users. Patches 1 and 2 move HARDENED_USERCOPY to the Kconfig.hardening and default it to disabled. Patch 3 moves FORTIFY_SOURCE to hardening only because the option is related to hardening and happened to be declared near HARDENED_USERCOPY. Building HARDENED_USERCOPY but disabled at runtime has neligible effect within the noise. Enabling the option by default generally incurs 2-10% of overhead depending on the workload with some extreme outliers depending on the exact CPU. While the benchmarks are somewhat synthetic, the overhead IO-intensive and network-intensive is easily detectable but the root cause may not be obvious (e.g. 2-14% overhead for netperf TCP_STREAM running over localhost with different ranges depending on the CPU). .../admin-guide/kernel-parameters.txt | 4 ++- mm/usercopy.c | 3 +- security/Kconfig | 21 ------------ security/Kconfig.hardening | 33 +++++++++++++++++++ 4 files changed, 38 insertions(+), 23 deletions(-) -- 2.43.0
