Re: [PATCH v4 14/16] sched/core: uclamp: request CAP_SYS_ADMIN by default

Juri Lelli
2018-09-04T13:47:56Z

Hi,

On 28/08/18 14:53, Patrick Bellasi wrote:
> The number of clamp groups supported is limited and defined at compile
> time. However, a malicious user can currently ask for many different

Even if not malicious.. :-)

> 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 <patrick.bellasi@arm.com>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> Cc: Paul Turner <pjt@google.com>
> Cc: Suren Baghdasaryan <surenb@google.com>
> Cc: Todd Kjos <tkjos@google.com>
> Cc: Joel Fernandes <joelaf@google.com>
> Cc: Steve Muckle <smuckle@google.com>
> Cc: Juri Lelli <juri.lelli@redhat.com>
> Cc: Quentin Perret <quentin.perret@arm.com>
> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Cc: Morten Rasmussen <morten.rasmussen@arm.com>
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-pm@vger.kernel.org
>
> ---
> 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)

Wondering if you want to fold the check below inside the

if (user && !capable(CAP_SYS_NICE)) {
...
}

block. It would also save you from adding another parameter to the
function.

> {
> 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;
> + }
> +

Best,

- Juri