perf-security: wrap paragraphs on 72 columns

Implemented formatting of paragraphs to be not wider than 72 columns.
Signed-off-by: Alexey Budankov <alexey.budankov@linux.intel.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/admin-guide/perf-security.rst

@@ -6,84 +6,94 @@ Perf Events and tool security
 Overview
 --------
 
-Usage of Performance Counters for Linux (perf_events) [1]_ , [2]_ , [3]_ can
-impose a considerable risk of leaking sensitive data accessed by monitored
-processes. The data leakage is possible both in scenarios of direct usage of
-perf_events system call API [2]_ and over data files generated by Perf tool user
-mode utility (Perf) [3]_ , [4]_ . The risk depends on the nature of data that
-perf_events performance monitoring units (PMU) [2]_ and Perf collect and expose
-for performance analysis. Collected system and performance data may be split into
-several categories:
-
-1. System hardware and software configuration data, for example: a CPU model and
-   its cache configuration, an amount of available memory and its topology, used
-   kernel and Perf versions, performance monitoring setup including experiment
-   time, events configuration, Perf command line parameters, etc.
-
-2. User and kernel module paths and their load addresses with sizes, process and
-   thread names with their PIDs and TIDs, timestamps for captured hardware and
-   software events.
-
-3. Content of kernel software counters (e.g., for context switches, page faults,
-   CPU migrations), architectural hardware performance counters (PMC) [8]_ and
-   machine specific registers (MSR) [9]_ that provide execution metrics for
-   various monitored parts of the system (e.g., memory controller (IMC), interconnect
-   (QPI/UPI) or peripheral (PCIe) uncore counters) without direct attribution to any
-   execution context state.
-
-4. Content of architectural execution context registers (e.g., RIP, RSP, RBP on
-   x86_64), process user and kernel space memory addresses and data, content of
-   various architectural MSRs that capture data from this category.
-
-Data that belong to the fourth category can potentially contain sensitive process
-data. If PMUs in some monitoring modes capture values of execution context registers
-or data from process memory then access to such monitoring capabilities requires
-to be ordered and secured properly. So, perf_events/Perf performance monitoring
-is the subject for security access control management [5]_ .
+Usage of Performance Counters for Linux (perf_events) [1]_ , [2]_ , [3]_
+can impose a considerable risk of leaking sensitive data accessed by
+monitored processes. The data leakage is possible both in scenarios of
+direct usage of perf_events system call API [2]_ and over data files
+generated by Perf tool user mode utility (Perf) [3]_ , [4]_ . The risk
+depends on the nature of data that perf_events performance monitoring
+units (PMU) [2]_ and Perf collect and expose for performance analysis.
+Collected system and performance data may be split into several
+categories:
+
+1. System hardware and software configuration data, for example: a CPU
+   model and its cache configuration, an amount of available memory and
+   its topology, used kernel and Perf versions, performance monitoring
+   setup including experiment time, events configuration, Perf command
+   line parameters, etc.
+
+2. User and kernel module paths and their load addresses with sizes,
+   process and thread names with their PIDs and TIDs, timestamps for
+   captured hardware and software events.
+
+3. Content of kernel software counters (e.g., for context switches, page
+   faults, CPU migrations), architectural hardware performance counters
+   (PMC) [8]_ and machine specific registers (MSR) [9]_ that provide
+   execution metrics for various monitored parts of the system (e.g.,
+   memory controller (IMC), interconnect (QPI/UPI) or peripheral (PCIe)
+   uncore counters) without direct attribution to any execution context
+   state.
+
+4. Content of architectural execution context registers (e.g., RIP, RSP,
+   RBP on x86_64), process user and kernel space memory addresses and
+   data, content of various architectural MSRs that capture data from
+   this category.
+
+Data that belong to the fourth category can potentially contain
+sensitive process data. If PMUs in some monitoring modes capture values
+of execution context registers or data from process memory then access
+to such monitoring capabilities requires to be ordered and secured
+properly. So, perf_events/Perf performance monitoring is the subject for
+security access control management [5]_ .
 
 perf_events/Perf access control
 -------------------------------
 
-To perform security checks, the Linux implementation splits processes into two
-categories [6]_ : a) privileged processes (whose effective user ID is 0, referred
-to as superuser or root), and b) unprivileged processes (whose effective UID is
-nonzero). Privileged processes bypass all kernel security permission checks so
-perf_events performance monitoring is fully available to privileged processes
-without access, scope and resource restrictions.
-
-Unprivileged processes are subject to a full security permission check based on
-the process's credentials [5]_ (usually: effective UID, effective GID, and
-supplementary group list).
-
-Linux divides the privileges traditionally associated with superuser into
-distinct units, known as capabilities [6]_ , which can be independently enabled
-and disabled on per-thread basis for processes and files of unprivileged users.
-
-Unprivileged processes with enabled CAP_SYS_ADMIN capability are treated as
-privileged processes with respect to perf_events performance monitoring and
-bypass *scope* permissions checks in the kernel.
-
-Unprivileged processes using perf_events system call API is also subject for
-PTRACE_MODE_READ_REALCREDS ptrace access mode check [7]_ , whose outcome
-determines whether monitoring is permitted. So unprivileged processes provided
-with CAP_SYS_PTRACE capability are effectively permitted to pass the check.
-
-Other capabilities being granted to unprivileged processes can effectively
-enable capturing of additional data required for later performance analysis of
-monitored processes or a system. For example, CAP_SYSLOG capability permits
-reading kernel space memory addresses from /proc/kallsyms file.
+To perform security checks, the Linux implementation splits processes
+into two categories [6]_ : a) privileged processes (whose effective user
+ID is 0, referred to as superuser or root), and b) unprivileged
+processes (whose effective UID is nonzero). Privileged processes bypass
+all kernel security permission checks so perf_events performance
+monitoring is fully available to privileged processes without access,
+scope and resource restrictions.
+
+Unprivileged processes are subject to a full security permission check
+based on the process's credentials [5]_ (usually: effective UID,
+effective GID, and supplementary group list).
+
+Linux divides the privileges traditionally associated with superuser
+into distinct units, known as capabilities [6]_ , which can be
+independently enabled and disabled on per-thread basis for processes and
+files of unprivileged users.
+
+Unprivileged processes with enabled CAP_SYS_ADMIN capability are treated
+as privileged processes with respect to perf_events performance
+monitoring and bypass *scope* permissions checks in the kernel.
+
+Unprivileged processes using perf_events system call API is also subject
+for PTRACE_MODE_READ_REALCREDS ptrace access mode check [7]_ , whose
+outcome determines whether monitoring is permitted. So unprivileged
+processes provided with CAP_SYS_PTRACE capability are effectively
+permitted to pass the check.
+
+Other capabilities being granted to unprivileged processes can
+effectively enable capturing of additional data required for later
+performance analysis of monitored processes or a system. For example,
+CAP_SYSLOG capability permits reading kernel space memory addresses from
+/proc/kallsyms file.
 
 perf_events/Perf privileged users
 ---------------------------------
 
-Mechanisms of capabilities, privileged capability-dumb files [6]_ and file system
-ACLs [10]_ can be used to create a dedicated group of perf_events/Perf privileged
-users who are permitted to execute performance monitoring without scope limits.
-The following steps can be taken to create such a group of privileged Perf users.
+Mechanisms of capabilities, privileged capability-dumb files [6]_ and
+file system ACLs [10]_ can be used to create a dedicated group of
+perf_events/Perf privileged users who are permitted to execute
+performance monitoring without scope limits. The following steps can be
+taken to create such a group of privileged Perf users.
 
-1. Create perf_users group of privileged Perf users, assign perf_users group to
-   Perf tool executable and limit access to the executable for other users in the
-   system who are not in the perf_users group:
+1. Create perf_users group of privileged Perf users, assign perf_users
+   group to Perf tool executable and limit access to the executable for
+   other users in the system who are not in the perf_users group:
 
 ::
 
@@ -97,8 +107,9 @@ The following steps can be taken to create such a group of privileged Perf users
    # ls -alhF
    -rwxr-x---  2 root perf_users  11M Oct 19 15:12 perf
 
-2. Assign the required capabilities to the Perf tool executable file and enable
-   members of perf_users group with performance monitoring privileges [6]_ :
+2. Assign the required capabilities to the Perf tool executable file and
+   enable members of perf_users group with performance monitoring
+   privileges [6]_ :
 
 ::
 
@@ -108,49 +119,52 @@ The following steps can be taken to create such a group of privileged Perf users
    # getcap perf
    perf = cap_sys_ptrace,cap_sys_admin,cap_syslog+ep
 
-As a result, members of perf_users group are capable of conducting performance
-monitoring by using functionality of the configured Perf tool executable that,
-when executes, passes perf_events subsystem scope checks.
+As a result, members of perf_users group are capable of conducting
+performance monitoring by using functionality of the configured Perf
+tool executable that, when executes, passes perf_events subsystem scope
+checks.
 
-This specific access control management is only available to superuser or root
-running processes with CAP_SETPCAP, CAP_SETFCAP [6]_ capabilities.
+This specific access control management is only available to superuser
+or root running processes with CAP_SETPCAP, CAP_SETFCAP [6]_
+capabilities.
 
 perf_events/Perf unprivileged users
 -----------------------------------
 
-perf_events/Perf *scope* and *access* control for unprivileged processes is
-governed by perf_event_paranoid [2]_ setting:
+perf_events/Perf *scope* and *access* control for unprivileged processes
+is governed by perf_event_paranoid [2]_ setting:
 
 -1:
-     Impose no *scope* and *access* restrictions on using perf_events performance
-     monitoring. Per-user per-cpu perf_event_mlock_kb [2]_ locking limit is
-     ignored when allocating memory buffers for storing performance data.
-     This is the least secure mode since allowed monitored *scope* is
-     maximized and no perf_events specific limits are imposed on *resources*
-     allocated for performance monitoring.
+     Impose no *scope* and *access* restrictions on using perf_events
+     performance monitoring. Per-user per-cpu perf_event_mlock_kb [2]_
+     locking limit is ignored when allocating memory buffers for storing
+     performance data. This is the least secure mode since allowed
+     monitored *scope* is maximized and no perf_events specific limits
+     are imposed on *resources* allocated for performance monitoring.
 
 >=0:
      *scope* includes per-process and system wide performance monitoring
-     but excludes raw tracepoints and ftrace function tracepoints monitoring.
-     CPU and system events happened when executing either in user or
-     in kernel space can be monitored and captured for later analysis.
-     Per-user per-cpu perf_event_mlock_kb locking limit is imposed but
-     ignored for unprivileged processes with CAP_IPC_LOCK [6]_ capability.
+     but excludes raw tracepoints and ftrace function tracepoints
+     monitoring. CPU and system events happened when executing either in
+     user or in kernel space can be monitored and captured for later
+     analysis. Per-user per-cpu perf_event_mlock_kb locking limit is
+     imposed but ignored for unprivileged processes with CAP_IPC_LOCK
+     [6]_ capability.
 
 >=1:
-     *scope* includes per-process performance monitoring only and excludes
-     system wide performance monitoring. CPU and system events happened when
-     executing either in user or in kernel space can be monitored and
-     captured for later analysis. Per-user per-cpu perf_event_mlock_kb
-     locking limit is imposed but ignored for unprivileged processes with
-     CAP_IPC_LOCK capability.
+     *scope* includes per-process performance monitoring only and
+     excludes system wide performance monitoring. CPU and system events
+     happened when executing either in user or in kernel space can be
+     monitored and captured for later analysis. Per-user per-cpu
+     perf_event_mlock_kb locking limit is imposed but ignored for
+     unprivileged processes with CAP_IPC_LOCK capability.
 
 >=2:
-     *scope* includes per-process performance monitoring only. CPU and system
-     events happened when executing in user space only can be monitored and
-     captured for later analysis. Per-user per-cpu perf_event_mlock_kb
-     locking limit is imposed but ignored for unprivileged processes with
-     CAP_IPC_LOCK capability.
+     *scope* includes per-process performance monitoring only. CPU and
+     system events happened when executing in user space only can be
+     monitored and captured for later analysis. Per-user per-cpu
+     perf_event_mlock_kb locking limit is imposed but ignored for
+     unprivileged processes with CAP_IPC_LOCK capability.
 
 perf_events/Perf resource control
 ---------------------------------
@@ -158,39 +172,45 @@ perf_events/Perf resource control
 Open file descriptors
 +++++++++++++++++++++
 
-The perf_events system call API [2]_ allocates file descriptors for every configured
-PMU event. Open file descriptors are a per-process accountable resource governed
-by the RLIMIT_NOFILE [11]_ limit (ulimit -n), which is usually derived from the login
-shell process. When configuring Perf collection for a long list of events on a
-large server system, this limit can be easily hit preventing required monitoring
-configuration. RLIMIT_NOFILE limit can be increased on per-user basis modifying
-content of the limits.conf file [12]_ . Ordinarily, a Perf sampling session
-(perf record) requires an amount of open perf_event file descriptors that is not
-less than the number of monitored events multiplied by the number of monitored CPUs.
+The perf_events system call API [2]_ allocates file descriptors for
+every configured PMU event. Open file descriptors are a per-process
+accountable resource governed by the RLIMIT_NOFILE [11]_ limit
+(ulimit -n), which is usually derived from the login shell process. When
+configuring Perf collection for a long list of events on a large server
+system, this limit can be easily hit preventing required monitoring
+configuration. RLIMIT_NOFILE limit can be increased on per-user basis
+modifying content of the limits.conf file [12]_ . Ordinarily, a Perf
+sampling session (perf record) requires an amount of open perf_event
+file descriptors that is not less than the number of monitored events
+multiplied by the number of monitored CPUs.
 
 Memory allocation
 +++++++++++++++++
 
-The amount of memory available to user processes for capturing performance monitoring
-data is governed by the perf_event_mlock_kb [2]_ setting. This perf_event specific
-resource setting defines overall per-cpu limits of memory allowed for mapping
-by the user processes to execute performance monitoring. The setting essentially
-extends the RLIMIT_MEMLOCK [11]_ limit, but only for memory regions mapped specifically
-for capturing monitored performance events and related data.
-
-For example, if a machine has eight cores and perf_event_mlock_kb limit is set
-to 516 KiB, then a user process is provided with 516 KiB * 8 = 4128 KiB of memory
-above the RLIMIT_MEMLOCK limit (ulimit -l) for perf_event mmap buffers. In particular,
-this means that, if the user wants to start two or more performance monitoring
-processes, the user is required to manually distribute the available 4128 KiB between the
-monitoring processes, for example, using the --mmap-pages Perf record mode option.
-Otherwise, the first started performance monitoring process allocates all available
-4128 KiB and the other processes will fail to proceed due to the lack of memory.
-
-RLIMIT_MEMLOCK and perf_event_mlock_kb resource constraints are ignored for
-processes with the CAP_IPC_LOCK capability. Thus, perf_events/Perf privileged users
-can be provided with memory above the constraints for perf_events/Perf performance
-monitoring purpose by providing the Perf executable with CAP_IPC_LOCK capability.
+The amount of memory available to user processes for capturing
+performance monitoring data is governed by the perf_event_mlock_kb [2]_
+setting. This perf_event specific resource setting defines overall
+per-cpu limits of memory allowed for mapping by the user processes to
+execute performance monitoring. The setting essentially extends the
+RLIMIT_MEMLOCK [11]_ limit, but only for memory regions mapped
+specifically for capturing monitored performance events and related data.
+
+For example, if a machine has eight cores and perf_event_mlock_kb limit
+is set to 516 KiB, then a user process is provided with 516 KiB * 8 =
+4128 KiB of memory above the RLIMIT_MEMLOCK limit (ulimit -l) for
+perf_event mmap buffers. In particular, this means that, if the user
+wants to start two or more performance monitoring processes, the user is
+required to manually distribute the available 4128 KiB between the
+monitoring processes, for example, using the --mmap-pages Perf record
+mode option. Otherwise, the first started performance monitoring process
+allocates all available 4128 KiB and the other processes will fail to
+proceed due to the lack of memory.
+
+RLIMIT_MEMLOCK and perf_event_mlock_kb resource constraints are ignored
+for processes with the CAP_IPC_LOCK capability. Thus, perf_events/Perf
+privileged users can be provided with memory above the constraints for
+perf_events/Perf performance monitoring purpose by providing the Perf
+executable with CAP_IPC_LOCK capability.
 
 Bibliography
 ------------