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Date: Wed, 27 Jul 2016 13:43:59 -0700
From: Kees Cook <keescook@...omium.org>
To: Jeff Vander Stoep <jeffv@...gle.com>
Cc: "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>, Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] security, perf: Add config option to restrict perf_event_open
On Wed, Jul 27, 2016 at 7:46 AM, Jeff Vander Stoep <jeffv@...gle.com> wrote:
> When CONFIG_SECURITY_PERF_EVENTS_RESTRICT=y 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.
>
> This new level of restriction is intended to reduce the attack
> surface of the kernel. It allows for a safe default to be set on
> production systems at build time while leaving a simple means for
> developers to grant access.
>
> Signed-off-by: Jeff Vander Stoep <jeffv@...gle.com>
Reviewed-by: Kees Cook <keescook@...omium.org>
-Kees
> ---
> Documentation/sysctl/kernel.txt | 3 ++-
> kernel/events/core.c | 4 ++++
> security/Kconfig | 9 +++++++++
> 3 files changed, 15 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
> index fac9798..52daff6 100644
> --- a/Documentation/sysctl/kernel.txt
> +++ b/Documentation/sysctl/kernel.txt
> @@ -659,7 +659,8 @@ allowed to execute.
> perf_event_paranoid:
>
> Controls use of the performance events system by unprivileged
> -users (without CAP_SYS_ADMIN). The default value is 2.
> +users (without CAP_SYS_ADMIN). The default value is 3 if
> +CONFIG_SECURITY_PERF_EVENTS_RESTRICT is set, or 2 otherwise.
>
> -1: Allow use of (almost) all events by all users
> >=0: Disallow raw tracepoint access by users without CAP_IOC_LOCK
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 52bd100..df9df87 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -355,7 +355,11 @@ static struct srcu_struct pmus_srcu;
> * 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 = 2;
> +#endif
>
> /* Minimum for 512 kiB + 1 user control page */
> int sysctl_perf_event_mlock __read_mostly = 512 + (PAGE_SIZE / 1024); /* 'free' kiB per user */
> diff --git a/security/Kconfig b/security/Kconfig
> index df28f2b..2a93551 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
> --
> 2.8.0.rc3.226.g39d4020
>
--
Kees Cook
Chrome OS & Brillo Security
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