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security, perf: Add config option to restrict perf_event_open

PATCH NAK Jeff Vander Stoep 3 participants 4 messages Jul 27, 2016 – Aug 2, 2016

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Jeff Vander Stoep

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#0 lore raw

PATCH 2/2 security, perf: Add config option to restrict perf_event_open

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 <[email protected]>
---
 Documentation/sysctl/kernel.txt | 3 ++-
 kernel/events/core.c            | 4 ++++
 security/Kconfig                | 9 +++++++++
 3 files changed, 15 insertions(+), 1 deletion(-)
Documentation/sysctl/kernel.txt +2 -1
index fac9798..52daff6 100644
@@ -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
kernel/events/core.c +4 -0
index 52bd100..df9df87 100644
@@ -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 */
security/Kconfig +9 -0
index df28f2b..2a93551 100644
@@ -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
Signature · 1 line
2.8.0.rc3.226.g39d4020
Reviewed-by on v1 2/2
#1 lore raw
Quoted 10 lines · Jeff Vander Stoep

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 <[email protected]>
Reviewed-by Kees Cook <[email protected]>

-Kees

Quoted 59 lines
---
 Documentation/sysctl/kernel.txt | 3 ++-
 kernel/events/core.c            | 4 ++++
 security/Kconfig                | 9 +++++++++
 3 files changed, 15 insertions(+), 1 deletion(-)
Documentation/sysctl/kernel.txt +2 -1
index fac9798..52daff6 100644
@@ -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
kernel/events/core.c +4 -0
index 52bd100..df9df87 100644
@@ -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 */
security/Kconfig +9 -1
index df28f2b..2a93551 100644
@@ -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

Signature · 2 lines
Kees Cook
Chrome OS & Brillo Security
maintainer NAK
#2 lore raw
In reply to Jeff Vander Stoep
Quoted 19 lines · Jeff Vander Stoep

+++ b/kernel/events/core.c

kernel/events/core.c +4 -0
@@ -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 */
security/Kconfig +0 -0
index df28f2b..2a93551 100644
@@ -18,6 +18,15 @@ config SECURITY_DMESG_RESTRICT

security/Kconfig config SECURITY_DMESG_RESTRICT · line 28

Quoted 10 lines
security/Kconfig +8 -0
 	  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.

NAK.

Apart from the fact that I hate the 3 thing this is not how you do default CONFIG knobs for !bool state variables.

Use an "int" config not a "bool" config and allow all options to be default.

#3 lore raw
Quoted 33 lines · Peter Zijlstra
Quoted 19 lines · Jeff Vander Stoep

+++ b/kernel/events/core.c

kernel/events/core.c +4 -0
@@ -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 */
security/Kconfig +0 -0
index df28f2b..2a93551 100644
@@ -18,6 +18,15 @@ config SECURITY_DMESG_RESTRICT

security/Kconfig config SECURITY_DMESG_RESTRICT · line 28

Quoted 10 lines
security/Kconfig +8 -0
        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.

NAK.

Quoted 5 lines

Apart from the fact that I hate the 3 thing this is not how you do default CONFIG knobs for !bool state variables.

Use an "int" config not a "bool" config and allow all options to be default.

How about leaving off 2/2 and just keeping 1/2 of this series?

-Kees

Signature · 2 lines
Kees Cook
Chrome OS & Brillo Security