1 files changed, 21 insertions, 0 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index aa47be71df4c..9cfd6bb9198e 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2657,6 +2657,27 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
         vmpoff=         [KNL,S390] Perform z/VM CP command after power off.
                         Format: <command>
 
+        vsyscall=       [X86-64]
+                        Controls the behavior of vsyscalls (i.e. calls to
+                        fixed addresses of 0xffffffffff600x00 from legacy
+                        code).  Most statically-linked binaries and older
+                        versions of glibc use these calls.  Because these
+                        functions are at fixed addresses, they make nice
+                        targets for exploits that can control RIP.
+
+                        emulate     [default] Vsyscalls turn into traps and are
+                                    emulated reasonably safely.
+
+                        native      Vsyscalls are native syscall instructions.
+                                    This is a little bit faster than trapping
+                                    and makes a few dynamic recompilers work
+                                    better than they would in emulation mode.
+                                    It also makes exploits much easier to write.
+
+                        none        Vsyscalls don't work at all.  This makes
+                                    them quite hard to use for exploits but
+                                    might break your system.
+
         vt.cur_default= [VT] Default cursor shape.
                         Format: 0xCCBBAA, where AA, BB, and CC are the same as
                         the parameters of the <Esc>[?A;B;Cc escape sequence;