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

["Vladimir D. Seleznev" <vseleznv@altlinux.org>]

On Thu, Jun 02, 2022 at 09:42:03PM +0300, Andrey Savchenko wrote:
> On Thu, 2 Jun 2022 21:26:36 +0300 Vladimir D. Seleznev wrote:
> > On Thu, Jun 02, 2022 at 06:58:41PM +0300, Andrey Savchenko wrote:
> > > On Thu, 2 Jun 2022 15:40:38 +0300 Vitaly Chikunov wrote:
> > > > Dmitry,
> > > > 
> > > > On Thu, Jun 02, 2022 at 10:14:38AM +0300, Dmitry V. Levin wrote:
> > > > > 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
> > > > > -------------------------^
> > > > 
> > > > Я это заметил, но, думаю, так надо и оставить.
> > > 
> > > Можно пояснить зачем? Какие задачи планируется этим решить?
> > > Считается ли нормальным, что профилировать нужно будет под рутом?
> > > Всё же хотелось бы, чтоб пользователь мог полноценно заниматься
> > > разработкой и отладкой приложений.
> > 
> > Не сказать, что профилирование — типичная задача. Если есть потребность
> > профилировать не из-под рута, то ничего не мешает переключить ручку на
> > подходящее значение.
> 
> И сделать ребут, да?
> 
> А профилирование ведь не только разработчику нужно, но и админу,
> особенно на высоконагруженных системах для поиска узких мест.
> 
> Т.е. в реальности всё будет от рута делаться и безопасность
> промышленных систем и систем разработки будет деградирована.

Насколько я помню, суперпользователь умеет сбрасывать привилегии.

-- 
   WBR,
   Vladimir D. Seleznev