On 06/26/2018 08:50 AM, Chris von Recklinghausen wrote:
> Enabling HARDENED_USER_COPY causes measurable regressions in the
> networking performances, up to 8% under UDP flood.
>
> A generic distro may want to enable HARDENED_USER_COPY in their default
> kernel config, but at the same time, such distro may want to be able to
> avoid the performance penalties in with the default configuration and
> disable the stricter check on a per-boot basis.
>
> This change adds a boot parameter that to conditionally disable
> HARDENED_USERCOPY at boot time.
>
> v1->v2:
> remove CONFIG_HUC_DEFAULT_OFF
> default is now enabled, boot param disables
> move check to __check_object_size so as to not break optimization of
> __builtin_constant_p()
> include linux/atomic.h before linux/jump_label.h
>
> Signed-off-by: Chris von Recklinghausen <crecklin@xxxxxxxxxx>
> ---
> .../admin-guide/kernel-parameters.rst | 1 +
> .../admin-guide/kernel-parameters.txt | 3 +++
> include/linux/thread_info.h | 5 ++++
> mm/usercopy.c | 27 +++++++++++++++++++
> 4 files changed, 36 insertions(+)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.rst b/Documentation/admin-guide/kernel-parameters.rst
> index b8d0bc07ed0a..87a1200a1db6 100644
> --- a/Documentation/admin-guide/kernel-parameters.rst
> +++ b/Documentation/admin-guide/kernel-parameters.rst
> @@ -100,6 +100,7 @@ parameter is applicable::
> FB The frame buffer device is enabled.
> FTRACE Function tracing enabled.
> GCOV GCOV profiling is enabled.
> + HUC Hardened usercopy is enabled
> HW Appropriate hardware is enabled.
> IA-64 IA-64 architecture is enabled.
> IMA Integrity measurement architecture is enabled.
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index efc7aa7a0670..d14be0038aed 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -816,6 +816,9 @@
> disable= [IPV6]
> See Documentation/networking/ipv6.txt.
>
> + disable_hardened_usercopy [HUC]
> + Disable hardened usercopy checks
> +
> disable_radix [PPC]
> Disable RADIX MMU mode on POWER9
>
> diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
> index 8d8821b3689a..ab24fe2d3f87 100644
> --- a/include/linux/thread_info.h
> +++ b/include/linux/thread_info.h
> @@ -109,6 +109,11 @@ static inline int arch_within_stack_frames(const void * const stack,
> #endif
>
> #ifdef CONFIG_HARDENED_USERCOPY
> +#include <linux/atomic.h>
> +#include <linux/jump_label.h>
> +
> +DECLARE_STATIC_KEY_FALSE(bypass_usercopy_checks);
> +
> extern void __check_object_size(const void *ptr, unsigned long n,
> bool to_user);
>
> diff --git a/mm/usercopy.c b/mm/usercopy.c
> index e9e9325f7638..6a1265e1a54e 100644
> --- a/mm/usercopy.c
> +++ b/mm/usercopy.c
> @@ -20,6 +20,8 @@
> #include <linux/sched/task.h>
> #include <linux/sched/task_stack.h>
> #include <linux/thread_info.h>
> +#include <linux/atomic.h>
> +#include <linux/jump_label.h>
> #include <asm/sections.h>
>
> /*
> @@ -248,6 +250,9 @@ static inline void check_heap_object(const void *ptr, unsigned long n,
> */
> void __check_object_size(const void *ptr, unsigned long n, bool to_user)
> {
> + if (static_branch_likely(&bypass_usercopy_checks))
> + return;
> +
> /* Skip all tests if size is zero. */
> if (!n)
> return;
> @@ -279,3 +284,25 @@ void __check_object_size(const void *ptr, unsigned long n, bool to_user)
> check_kernel_text_object((const unsigned long)ptr, n, to_user);
> }
> EXPORT_SYMBOL(__check_object_size);
> +
> +DEFINE_STATIC_KEY_FALSE(bypass_usercopy_checks);
> +EXPORT_SYMBOL(bypass_usercopy_checks);
> +
> +static bool disable_huc_atboot = false;
> +
> +static int __init parse_disable_usercopy(char *str)
> +{
> + disable_huc_atboot = true;
> + return 1;
> +}
> +
> +static int __init set_disable_usercopy(void)
> +{
> + if (disable_huc_atboot == true)
> + static_branch_enable(&bypass_usercopy_checks);
> + return 1;
> +}
> +
> +__setup("disable_hardened_usercopy", parse_disable_usercopy);
> +
> +late_initcall(set_disable_usercopy);
