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Date: Mon, 25 Jun 2018 12:44:22 -0700
From: Laura Abbott <labbott@...hat.com>
To: Christoph von Recklinghausen <crecklin@...hat.com>,
keescook@...omium.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org
Subject: Re: [PATCH] add param that allows bootline control of hardened
usercopy
On 06/25/2018 08:22 AM, Christoph von Recklinghausen wrote:
> Add correct address for linux-mm
>
> On 06/25/2018 11:08 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
>> enable the stricter check on a per-boot basis.
>>
>> This change adds a config variable and a boot parameter to conditionally
>> enable HARDENED_USER_COPY at boot time, and switch HUC to off if
>> HUC_DEFAULT_OFF is set.
>>
>> Signed-off-by: Chris von Recklinghausen <crecklin@...hat.com>
>> ---
>> .../admin-guide/kernel-parameters.rst | 2 ++
>> .../admin-guide/kernel-parameters.txt | 3 ++
>> include/linux/thread_info.h | 7 +++++
>> mm/usercopy.c | 28 +++++++++++++++++++
>> security/Kconfig | 10 +++++++
>> 5 files changed, 50 insertions(+)
>>
>> diff --git a/Documentation/admin-guide/kernel-parameters.rst b/Documentation/admin-guide/kernel-parameters.rst
>> index b8d0bc07ed0a..c3035038e3ae 100644
>> --- a/Documentation/admin-guide/kernel-parameters.rst
>> +++ b/Documentation/admin-guide/kernel-parameters.rst
>> @@ -100,6 +100,8 @@ parameter is applicable::
>> FB The frame buffer device is enabled.
>> FTRACE Function tracing enabled.
>> GCOV GCOV profiling is enabled.
>> + HUC Hardened usercopy is enabled
>> + HUCF Hardened usercopy disabled at boot
>> 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..cd3354bc14d3 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.
>>
>> + enable_hardened_usercopy [HUC,HUCF]
>> + Enable 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..140a36cc1c2c 100644
>> --- a/include/linux/thread_info.h
>> +++ b/include/linux/thread_info.h
>> @@ -109,12 +109,19 @@ static inline int arch_within_stack_frames(const void * const stack,
>> #endif
>>
>> #ifdef CONFIG_HARDENED_USERCOPY
>> +#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);
>>
>> static __always_inline void check_object_size(const void *ptr, unsigned long n,
>> bool to_user)
>> {
>> + if (static_branch_likely(&bypass_usercopy_checks))
>> + return;
>> +
>> if (!__builtin_constant_p(n))
>> __check_object_size(ptr, n, to_user);
>> }
>> diff --git a/mm/usercopy.c b/mm/usercopy.c
>> index e9e9325f7638..ce3996da1b2e 100644
>> --- a/mm/usercopy.c
>> +++ b/mm/usercopy.c
>> @@ -279,3 +279,31 @@ 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);
>> +
>> +#ifdef CONFIG_HUC_DEFAULT_OFF
>> +#define HUC_DEFAULT false
>> +#else
>> +#define HUC_DEFAULT true
>> +#endif
>> +
>> +static bool enable_huc_atboot = HUC_DEFAULT;
>> +
>> +static int __init parse_enable_usercopy(char *str)
>> +{
>> + enable_huc_atboot = true;
>> + return 1;
>> +}
>> +
>> +static int __init set_enable_usercopy(void)
>> +{
>> + if (enable_huc_atboot == false)
>> + static_branch_enable(&bypass_usercopy_checks);
>> + return 1;
>> +}
>> +
>> +__setup("enable_hardened_usercopy", parse_enable_usercopy);
>> +
>> +late_initcall(set_enable_usercopy);
>> diff --git a/security/Kconfig b/security/Kconfig
>> index c4302067a3ad..a6173897b85c 100644
>> --- a/security/Kconfig
>> +++ b/security/Kconfig
>> @@ -189,6 +189,16 @@ config HARDENED_USERCOPY_PAGESPAN
>> been removed. This config is intended to be used only while
>> trying to find such users.
>>
>> +config HUC_DEFAULT_OFF
>> + bool "allow CONFIG_HARDENED_USERCOPY to be configured but disabled"
>> + depends on HARDENED_USERCOPY
>> + help
>> + When CONFIG_HARDENED_USERCOPY is enabled, disable its
>> + functionality unless it is enabled via at boot time
>> + via the "enable_hardened_usercopy" boot parameter. This allows
>> + the functionality of hardened usercopy to be present but not
>> + impact performance unless it is needed.
>> +
>> config FORTIFY_SOURCE
>> bool "Harden common str/mem functions against buffer overflows"
>> depends on ARCH_HAS_FORTIFY_SOURCE
>
>
This seems a bit backwards, I'd much rather see hardened user copy
default to on with the basic config option and then just have a command
line option to turn it off.
Thanks,
Laura
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