The number of clamp groups supported is limited and defined at compile time. However, a malicious user can currently ask for many different clamp values thus consuming all the available clamp groups.
Since on properly configured systems we expect only a limited set of different clamp values, the previous problem can be mitigated by allowing access to clamp groups configuration only to privileged tasks. This should still allow a System Management Software to properly pre-configure the system. Let's restrict the tuning of utilization clamp values, by default, to tasks with CAP_SYS_ADMIN capabilities. Whenever this should be considered too restrictive and/or not required for a specific platforms, a kernel boot option is provided to change this default behavior thus allowing non privileged tasks to change their utilization clamp values. Signed-off-by: Patrick Bellasi <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Rafael J. Wysocki <[email protected]> Cc: Paul Turner <[email protected]> Cc: Suren Baghdasaryan <[email protected]> Cc: Todd Kjos <[email protected]> Cc: Joel Fernandes <[email protected]> Cc: Steve Muckle <[email protected]> Cc: Juri Lelli <[email protected]> Cc: Quentin Perret <[email protected]> Cc: Dietmar Eggemann <[email protected]> Cc: Morten Rasmussen <[email protected]> Cc: [email protected] Cc: [email protected] --- Changes in v4: Others: - new patch added in this version - rebased on v4.19-rc1 --- .../admin-guide/kernel-parameters.txt | 3 +++ kernel/sched/core.c | 22 ++++++++++++++++--- 2 files changed, 22 insertions(+), 3 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 9871e649ffef..481f8214ea9a 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -4561,6 +4561,9 @@ <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> See also Documentation/input/devices/joystick-parport.rst + uclamp_user [KNL] Enable task-specific utilization clamping tuning + also from tasks without CAP_SYS_ADMIN capability. + udbg-immortal [PPC] When debugging early kernel crashes that happen after console_init() and before a proper console driver takes over, this boot options might diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 222397edb8a7..8341ce580a9a 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1510,14 +1510,29 @@ static inline int alloc_uclamp_sched_group(struct task_group *tg, static inline void free_uclamp_sched_group(struct task_group *tg) { } #endif /* CONFIG_UCLAMP_TASK_GROUP */ +static bool uclamp_user_allowed __read_mostly; +static int __init uclamp_user_allow(char *str) +{ + uclamp_user_allowed = true; + + return 0; +} +early_param("uclamp_user", uclamp_user_allow); + static inline int __setscheduler_uclamp(struct task_struct *p, - const struct sched_attr *attr) + const struct sched_attr *attr, + bool user) { int group_id[UCLAMP_CNT] = { UCLAMP_NOT_VALID }; int lower_bound, upper_bound; struct uclamp_se *uc_se; int result = 0; + if (!capable(CAP_SYS_ADMIN) && + user && !uclamp_user_allowed) { + return -EPERM; + } + mutex_lock(&uclamp_mutex); /* Find a valid group_id for each required clamp value */ @@ -1702,7 +1717,8 @@ static inline int alloc_uclamp_sched_group(struct task_group *tg, return 1; } static inline int __setscheduler_uclamp(struct task_struct *p, - const struct sched_attr *attr) + const struct sched_attr *attr, + bool user) { return -EINVAL; } @@ -5217,7 +5233,7 @@ static int __sched_setscheduler(struct task_struct *p, /* Configure utilization clamps for the task */ if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP) { - retval = __setscheduler_uclamp(p, attr); + retval = __setscheduler_uclamp(p, attr, user); if (retval) return retval; } -- 2.18.0
