1 files changed, 42 insertions, 0 deletions

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index 0ec91f03422e..a76a26a1db8a 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -41,6 +41,8 @@ Table of Contents
   3.5   /proc/<pid>/mountinfo - Information about mounts
   3.6   /proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
 
+  4     Configuring procfs
+  4.1   Mount options
 
 ------------------------------------------------------------------------------
 Preface
@@ -305,6 +307,9 @@ Table 1-4: Contents of the stat files (as of 2.6.30-rc7)
   blkio_ticks   time spent waiting for block IO
   gtime         guest time of the task in jiffies
   cgtime        guest time of the task children in jiffies
+  start_data    address above which program data+bss is placed
+  end_data      address below which program data+bss is placed
+  start_brk     address above which program heap can be expanded with brk()
 ..............................................................................
 
 The /proc/PID/maps file containing the currently mapped memory regions and
@@ -1542,3 +1547,40 @@ a task to set its own or one of its thread siblings comm value. The comm value
 is limited in size compared to the cmdline value, so writing anything longer
 then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
 comm value.
+
+
+------------------------------------------------------------------------------
+Configuring procfs
+------------------------------------------------------------------------------
+
+4.1     Mount options
+---------------------
+
+The following mount options are supported:
+
+        hidepid=        Set /proc/<pid>/ access mode.
+        gid=            Set the group authorized to learn processes information.
+
+hidepid=0 means classic mode - everybody may access all /proc/<pid>/ directories
+(default).
+
+hidepid=1 means users may not access any /proc/<pid>/ directories but their
+own.  Sensitive files like cmdline, sched*, status are now protected against
+other users.  This makes it impossible to learn whether any user runs
+specific program (given the program doesn't reveal itself by its behaviour).
+As an additional bonus, as /proc/<pid>/cmdline is unaccessible for other users,
+poorly written programs passing sensitive information via program arguments are
+now protected against local eavesdroppers.
+
+hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be fully invisible to other
+users.  It doesn't mean that it hides a fact whether a process with a specific
+pid value exists (it can be learned by other means, e.g. by "kill -0 $PID"),
+but it hides process' uid and gid, which may be learned by stat()'ing
+/proc/<pid>/ otherwise.  It greatly complicates an intruder's task of gathering
+information about running processes, whether some daemon runs with elevated
+privileges, whether other user runs some sensitive program, whether other users
+run any program at all, etc.
+
+gid= defines a group authorized to learn processes information otherwise
+prohibited by hidepid=.  If you use some daemon like identd which needs to learn
+information about processes information, just add identd to this group.