Merge branch 'x86-vdso-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git...

[GitHub/mt8127/android_kernel_alcatel_ttab.git] / Documentation / kernel-parameters.txt

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index e279b724291239677041f3d4a3f002e566db8ae6..78926aa2531cd36691e154a06fcfbed831726b04 100644 (file)
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2680,6 +2680,27 @@ 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;