[PATCH RFC] perf_event: Add support for LSM and SELinux checks
Peter Zijlstra
peterz at infradead.org
Thu Oct 10 08:12:51 UTC 2019
On Wed, Oct 09, 2019 at 04:36:57PM -0400, Joel Fernandes (Google) wrote:
> In currentl mainline, the degree of access to perf_event_open(2) system
> call depends on the perf_event_paranoid sysctl. This has a number of
> limitations:
>
> 1. The sysctl is only a single value. Many types of accesses are controlled
> based on the single value thus making the control very limited and
> coarse grained.
> 2. The sysctl is global, so if the sysctl is changed, then that means
> all processes get access to perf_event_open(2) opening the door to
> security issues.
>
> This patch adds LSM and SELinux access checking which will be used in
> Android to access perf_event_open(2) for the purposes of attaching BPF
> programs to tracepoints, perf profiling and other operations from
> userspace. These operations are intended for production systems.
>
> 5 new LSM hooks are added:
> 1. perf_event_open: This controls access during the perf_event_open(2)
> syscall itself. The hook is called from all the places that the
> perf_event_paranoid sysctl is checked to keep it consistent with the
> systctl. The hook gets passed a 'type' argument which controls CPU,
> kernel and tracepoint accesses (in this context, CPU, kernel and
> tracepoint have the same semantics as the perf_event_paranoid sysctl).
> Additionally, I added an 'open' type which is similar to
> perf_event_paranoid sysctl == 3 patch carried in Android and several other
> distros but was rejected in mainline [1] in 2016.
>
> 2. perf_event_alloc: This allocates a new security object for the event
> which stores the current SID within the event. It will be useful when
> the perf event's FD is passed through IPC to another process which may
> try to read the FD. Appropriate security checks will limit access.
>
> 3. perf_event_free: Called when the event is closed.
>
> 4. perf_event_read: Called from the read(2) system call path for the event.
+ mmap()
>
> 5. perf_event_write: Called from the read(2) system call path for the event.
- read() + ioctl()
fresh from the keyboard.. but maybe consoldate things a little.
---
--- a/arch/x86/events/intel/bts.c
+++ b/arch/x86/events/intel/bts.c
@@ -14,7 +14,6 @@
#include <linux/debugfs.h>
#include <linux/device.h>
#include <linux/coredump.h>
-#include <linux/security.h>
#include <linux/sizes.h>
#include <asm/perf_event.h>
@@ -550,13 +549,11 @@ static int bts_event_init(struct perf_ev
* Note that the default paranoia setting permits unprivileged
* users to profile the kernel.
*/
- if (event->attr.exclude_kernel && perf_paranoid_kernel() &&
- !capable(CAP_SYS_ADMIN))
- return -EACCES;
-
- ret = security_perf_event_open(&event->attr, PERF_SECURITY_KERNEL);
- if (ret)
- return ret;
+ if (event->attr.exclude_kernel) {
+ ret = perf_allow_kernel(&event->attr);
+ if (ret)
+ return ret;
+ }
if (x86_add_exclusive(x86_lbr_exclusive_bts))
return -EBUSY;
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -11,7 +11,6 @@
#include <linux/stddef.h>
#include <linux/types.h>
#include <linux/init.h>
-#include <linux/security.h>
#include <linux/slab.h>
#include <linux/export.h>
#include <linux/nmi.h>
@@ -3316,10 +3315,7 @@ static int intel_pmu_hw_config(struct pe
if (x86_pmu.version < 3)
return -EINVAL;
- if (perf_paranoid_cpu() && !capable(CAP_SYS_ADMIN))
- return -EACCES;
-
- ret = security_perf_event_open(&event->attr, PERF_SECURITY_CPU);
+ ret = perf_allow_cpu(&event->attr);
if (ret)
return ret;
--- a/arch/x86/events/intel/p4.c
+++ b/arch/x86/events/intel/p4.c
@@ -8,7 +8,6 @@
*/
#include <linux/perf_event.h>
-#include <linux/security.h>
#include <asm/perf_event_p4.h>
#include <asm/hardirq.h>
@@ -777,10 +776,7 @@ static int p4_validate_raw_event(struct
* the user needs special permissions to be able to use it
*/
if (p4_ht_active() && p4_event_bind_map[v].shared) {
- if (perf_paranoid_cpu() && !capable(CAP_SYS_ADMIN))
- return -EACCES;
-
- v = security_perf_event_open(&event->attr, PERF_SECURITY_CPU);
+ v = perf_allow_cpu(&event->attr);
if (v)
return v;
}
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -56,6 +56,7 @@ struct perf_guest_info_callbacks {
#include <linux/perf_regs.h>
#include <linux/cgroup.h>
#include <linux/refcount.h>
+#include <linux/security.h>
#include <asm/local.h>
struct perf_callchain_entry {
@@ -1244,19 +1245,28 @@ extern int perf_cpu_time_max_percent_han
int perf_event_max_stack_handler(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp, loff_t *ppos);
-static inline bool perf_paranoid_tracepoint_raw(void)
+static inline int perf_allow_kernel(struct perf_event_attr *attr)
{
- return sysctl_perf_event_paranoid > -1;
+ if (sysctl_perf_event_paranoid > 1 && !capable(CAP_SYS_ADMIN))
+ return -EACCES;
+
+ return security_perf_event_open(attr, PERF_SECURITY_KERNEL);
}
-static inline bool perf_paranoid_cpu(void)
+static inline int perf_allow_cpu(struct perf_event_attr *attr)
{
- return sysctl_perf_event_paranoid > 0;
+ if (sysctl_perf_event_paranoid > 0 && !capable(CAP_SYS_ADMIN))
+ return -EACCES;
+
+ return security_perf_event_open(attr, PERF_SECURITY_CPU);
}
-static inline bool perf_paranoid_kernel(void)
+static inline int perf_allow_tracepoint(struct perf_event_attr *attr)
{
- return sysctl_perf_event_paranoid > 1;
+ if (sysctl_perf_event_paranoid > -1 && !capable(CAP_SYS_ADMIN))
+ return -EPERM;
+
+ return security_perf_event_open(attr, PERF_SECURITY_TRACEPOINT);
}
extern void perf_event_init(void);
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4229,10 +4229,7 @@ find_get_context(struct pmu *pmu, struct
if (!task) {
/* Must be root to operate on a CPU event: */
- if (perf_paranoid_cpu() && !capable(CAP_SYS_ADMIN))
- return ERR_PTR(-EACCES);
-
- err = security_perf_event_open(&event->attr, PERF_SECURITY_CPU);
+ err = perf_allow_cpu(&event->attr);
if (err)
return ERR_PTR(err);
@@ -5862,14 +5859,8 @@ static int perf_mmap(struct file *file,
lock_limit >>= PAGE_SHIFT;
locked = atomic64_read(&vma->vm_mm->pinned_vm) + extra;
- if (locked > lock_limit) {
- if (perf_paranoid_tracepoint_raw() && !capable(CAP_IPC_LOCK)) {
- ret = -EPERM;
- goto unlock;
- }
-
- ret = security_perf_event_open(&event->attr,
- PERF_SECURITY_TRACEPOINT);
+ if (locked > lock_limit && !capable(CAP_IPC_LOCK)) {
+ ret = perf_allow_tracepoint(&event->attr);
if (ret)
goto unlock;
}
@@ -10702,11 +10693,7 @@ static int perf_copy_attr(struct perf_ev
}
/* privileged levels capture (kernel, hv): check permissions */
if (mask & PERF_SAMPLE_BRANCH_PERM_PLM) {
- if (perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN))
- return -EACCES;
-
- ret = security_perf_event_open(attr,
- PERF_SECURITY_KERNEL);
+ ret = perf_allow_kernel(attr);
if (ret)
return ret;
}
@@ -10932,10 +10919,7 @@ SYSCALL_DEFINE5(perf_event_open,
return err;
if (!attr.exclude_kernel) {
- if (perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN))
- return -EACCES;
-
- err = security_perf_event_open(&attr, PERF_SECURITY_KERNEL);
+ err = perf_allow_kernel(&attr);
if (err)
return err;
}
@@ -10954,9 +10938,11 @@ SYSCALL_DEFINE5(perf_event_open,
}
/* Only privileged users can get physical addresses */
- if ((attr.sample_type & PERF_SAMPLE_PHYS_ADDR) &&
- perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN))
- return -EACCES;
+ if ((attr.sample_type & PERF_SAMPLE_PHYS_ADDR)) {
+ err = perf_allow_kernel(&attr);
+ if (err)
+ return err;
+ }
err = security_locked_down(LOCKDOWN_PERF);
if (err && (attr.sample_type & PERF_SAMPLE_REGS_INTR))
--- a/kernel/trace/trace_event_perf.c
+++ b/kernel/trace/trace_event_perf.c
@@ -49,11 +49,7 @@ static int perf_trace_event_perm(struct
/* The ftrace function trace is allowed only for root. */
if (ftrace_event_is_function(tp_event)) {
- if (perf_paranoid_tracepoint_raw() && !capable(CAP_SYS_ADMIN))
- return -EPERM;
-
- ret = security_perf_event_open(&p_event->attr,
- PERF_SECURITY_TRACEPOINT);
+ ret = perf_allow_tracepoint(&p->event->attr);
if (ret)
return ret;
@@ -90,11 +86,7 @@ static int perf_trace_event_perm(struct
* ...otherwise raw tracepoint data can be a severe data leak,
* only allow root to have these.
*/
- if (perf_paranoid_tracepoint_raw() && !capable(CAP_SYS_ADMIN))
- return -EPERM;
-
- ret = security_perf_event_open(&p_event->attr,
- PERF_SECURITY_TRACEPOINT);
+ ret = perf_allow_tracepoint(&p_event->attr);
if (ret)
return ret;
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