On Mon, Jan 11, 2016 at 7:23 AM, Ben Hutchings <ben@xxxxxxxxxxxxxxx> wrote:
> When kernel.perf_event_open is set to 3 (or greater), disallow all
> access to performance events by users without CAP_SYS_ADMIN.
> Add a Kconfig symbol CONFIG_SECURITY_PERF_EVENTS_RESTRICT that
> makes this value the default.
>
> This is based on a similar feature in grsecurity
> (CONFIG_GRKERNSEC_PERF_HARDEN). This version doesn't include making
> the variable read-only. It also allows enabling further restriction
> at run-time regardless of whether the default is changed.
>
> Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
Whoops, I entirely missed this email! Just found it now.
Ben, can you resend this with Perf maintainers in CC? This seems
sensible enough to me.
-Kees
> ---
> I made a similar change to Debian's kernel packages in August,
> including the more restrictive default, and no-one has complained yet.
>
> Ben.
>
> Documentation/sysctl/kernel.txt | 4 +++-
> include/linux/perf_event.h | 5 +++++
> kernel/events/core.c | 8 ++++++++
> security/Kconfig | 9 +++++++++
> 4 files changed, 25 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
> index 88a2c8e..76e2ca8 100644
> --- a/Documentation/sysctl/kernel.txt
> +++ b/Documentation/sysctl/kernel.txt
> @@ -629,12 +629,14 @@ allowed to execute.
> perf_event_paranoid:
>
> Controls use of the performance events system by unprivileged
> -users (without CAP_SYS_ADMIN). The default value is 1.
> +users (without CAP_SYS_ADMIN). The default value is 3 if
> +CONFIG_SECURITY_PERF_EVENTS_RESTRICT is set, or 1 otherwise.
>
> -1: Allow use of (almost) all events by all users
> >=0: Disallow raw tracepoint access by users without CAP_IOC_LOCK
> >=1: Disallow CPU event access by users without CAP_SYS_ADMIN
> >=2: Disallow kernel profiling by users without CAP_SYS_ADMIN
> +>=3: Disallow all event access by users without CAP_SYS_ADMIN
>
> ==============================================================
>
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index f9828a4..aa72940 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -989,6 +989,11 @@ extern int perf_cpu_time_max_percent_handler(struct ctl_table *table, int write,
> loff_t *ppos);
>
>
> +static inline bool perf_paranoid_any(void)
> +{
> + return sysctl_perf_event_paranoid > 2;
> +}
> +
> static inline bool perf_paranoid_tracepoint_raw(void)
> {
> return sysctl_perf_event_paranoid > -1;
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index cfc227c..85bc810 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -175,8 +175,13 @@ static struct srcu_struct pmus_srcu;
> * 0 - disallow raw tracepoint access for unpriv
> * 1 - disallow cpu events for unpriv
> * 2 - disallow kernel profiling for unpriv
> + * 3 - disallow all unpriv perf event use
> */
> +#ifdef CONFIG_SECURITY_PERF_EVENTS_RESTRICT
> +int sysctl_perf_event_paranoid __read_mostly = 3;
> +#else
> int sysctl_perf_event_paranoid __read_mostly = 1;
> +#endif
>
> /* Minimum for 512 kiB + 1 user control page */
> int sysctl_perf_event_mlock __read_mostly = 512 + (PAGE_SIZE / 1024); /* 'free' kiB per user */
> @@ -8265,6 +8270,9 @@ SYSCALL_DEFINE5(perf_event_open,
> if (flags & ~PERF_FLAG_ALL)
> return -EINVAL;
>
> + if (perf_paranoid_any() && !capable(CAP_SYS_ADMIN))
> + return -EACCES;
> +
> err = perf_copy_attr(attr_uptr, &attr);
> if (err)
> return err;
> diff --git a/security/Kconfig b/security/Kconfig
> index e452378..30a2603 100644
> --- a/security/Kconfig
> +++ b/security/Kconfig
> @@ -18,6 +18,15 @@ config SECURITY_DMESG_RESTRICT
>
> If you are unsure how to answer this question, answer N.
>
> +config SECURITY_PERF_EVENTS_RESTRICT
> + bool "Restrict unprivileged use of performance events"
> + depends on PERF_EVENTS
> + help
> + If you say Y here, the kernel.perf_event_paranoid sysctl
> + will be set to 3 by default, and no unprivileged use of the
> + perf_event_open syscall will be permitted unless it is
> + changed.
> +
> config SECURITY
> bool "Enable different security models"
> depends on SYSFS
--
Kees Cook
Chrome OS & Brillo Security
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