Re: [d-kernel] [PATCH] UBUNTU: SAUCE: security, perf: Allow further restriction of perf_event_open

["Dmitry V. Levin" <ldv@altlinux.org>]

On Thu, Jun 02, 2022 at 03:31:00AM +0300, Vitaly Chikunov wrote:
> From: Ben Hutchings <ben@decadent.org.uk>
> 
> https://lkml.org/lkml/2016/1/11/587
> 
> The GRKERNSEC_PERF_HARDEN feature extracted from grsecurity.  Adds the
> option to disable perf_event_open() entirely for unprivileged users.
> This standalone version doesn't include making the variable read-only
> (or renaming it).
> 
> 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@decadent.org.uk>
> Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
> [ saf: resolve conflicts with v5.8-rc1 ]
> Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
> [ vt: Make it default y. ]
> Signed-off-by: Vitaly Chikunov <vt@altlinux.org>
> ---
>  include/linux/perf_event.h |  6 ++++++
>  kernel/events/core.c       |  8 ++++++++
>  security/Kconfig           | 10 ++++++++++
>  3 files changed, 24 insertions(+)
> 
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 733649184b27..b00607abbcdf 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -1342,6 +1342,12 @@ int perf_event_max_stack_handler(struct ctl_table *table, int write,
>  #define PERF_SECURITY_CPU		1
>  #define PERF_SECURITY_KERNEL		2
>  #define PERF_SECURITY_TRACEPOINT	3
> +#define PERF_SECURITY_MAX		4
----------------------------------------^

> +
> +static inline bool perf_paranoid_any(void)
> +{
> +	return sysctl_perf_event_paranoid >= PERF_SECURITY_MAX;
> +}
>  
>  static inline int perf_is_paranoid(void)
>  {
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 2d7a23a7507b..15a3b37ae213 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -414,8 +414,13 @@ static struct kmem_cache *perf_event_cache;
>   *   0 - disallow raw tracepoint access for unpriv
>   *   1 - disallow cpu events for unpriv
>   *   2 - disallow kernel profiling for unpriv
> + *   4 - disallow all unpriv perf event use
--------^

>   */
> +#ifdef CONFIG_SECURITY_PERF_EVENTS_RESTRICT
> +int sysctl_perf_event_paranoid __read_mostly = PERF_SECURITY_MAX;
> +#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 */
> @@ -12148,6 +12153,9 @@ SYSCALL_DEFINE5(perf_event_open,
>  	if (err)
>  		return err;
>  
> +	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 6c7b35c941c7..4861085a2d49 100644
> --- a/security/Kconfig
> +++ b/security/Kconfig
> @@ -19,6 +19,16 @@ 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
> +	default y
> +	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
-------------------------^


-- 
ldv