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

Pull x86 vsyscall updates from Thomas Gleixner:
 "Further hardening of the legacy vsyscall by providing support for
  execute only mode and switching the default to it.

  This prevents a certain class of attacks which rely on the vsyscall
  page being accessible at a fixed address in the canonical kernel
  address space"

* 'x86-entry-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  selftests/x86: Add a test for process_vm_readv() on the vsyscall page
  x86/vsyscall: Add __ro_after_init to global variables
  x86/vsyscall: Change the default vsyscall mode to xonly
  selftests/x86/vsyscall: Verify that vsyscall=none blocks execution
  x86/vsyscall: Document odd SIGSEGV error code for vsyscalls
  x86/vsyscall: Show something useful on a read fault
  x86/vsyscall: Add a new vsyscall=xonly mode
  Documentation/admin: Remove the vsyscall=native documentation

diff --combined Documentation/admin-guide/kernel-parameters.txt
index b9b0623,be8c3a6..5c7a0f5
--- 1/Documentation/admin-guide/kernel-parameters.txt
--- 2/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@@ -478,7 -478,7 +478,7 @@@
                        others).
  
        ccw_timeout_log [S390]
 -                      See Documentation/s390/CommonIO for details.
 +                      See Documentation/s390/common_io.rst for details.
  
        cgroup_disable= [KNL] Disable a particular controller
                        Format: {name of the controller(s) to disable}
@@@ -516,7 -516,7 +516,7 @@@
                                /selinux/checkreqprot.
  
        cio_ignore=     [S390]
 -                      See Documentation/s390/CommonIO for details.
 +                      See Documentation/s390/common_io.rst for details.
        clk_ignore_unused
                        [CLK]
                        Prevents the clock framework from automatically gating
@@@ -5100,13 -5100,12 +5100,12 @@@
                        targets for exploits that can control RIP.
  
                        emulate     [default] Vsyscalls turn into traps and are
-                                   emulated reasonably safely.
+                                   emulated reasonably safely.  The vsyscall
+                                   page is readable.
  
-                       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.
+                       xonly       Vsyscalls turn into traps and are
+                                   emulated reasonably safely.  The vsyscall
+                                   page is not readable.
  
                        none        Vsyscalls don't work at all.  This makes
                                    them quite hard to use for exploits but

diff --combined arch/x86/Kconfig
index 51a98d6,32028ed..fbabf59
--- 1/arch/x86/Kconfig
--- 2/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@@ -17,7 -17,6 +17,7 @@@ config X86_3
        select HAVE_DEBUG_STACKOVERFLOW
        select MODULES_USE_ELF_REL
        select OLD_SIGACTION
 +      select GENERIC_VDSO_32
  
  config X86_64
        def_bool y
@@@ -122,7 -121,6 +122,7 @@@ config X8
        select GENERIC_STRNCPY_FROM_USER
        select GENERIC_STRNLEN_USER
        select GENERIC_TIME_VSYSCALL
 +      select GENERIC_GETTIMEOFDAY
        select HARDLOCKUP_CHECK_TIMESTAMP       if X86_64
        select HAVE_ACPI_APEI                   if ACPI
        select HAVE_ACPI_APEI_NMI               if ACPI
@@@ -204,7 -202,6 +204,7 @@@
        select HAVE_SYSCALL_TRACEPOINTS
        select HAVE_UNSTABLE_SCHED_CLOCK
        select HAVE_USER_RETURN_NOTIFIER
 +      select HAVE_GENERIC_VDSO
        select HOTPLUG_SMT                      if SMP
        select IRQ_FORCED_THREADING
        select NEED_SG_DMA_LENGTH
@@@ -2288,7 -2285,7 +2288,7 @@@ config COMPAT_VDS
  choice
        prompt "vsyscall table for legacy applications"
        depends on X86_64
-       default LEGACY_VSYSCALL_EMULATE
+       default LEGACY_VSYSCALL_XONLY
        help
          Legacy user code that does not know how to find the vDSO expects
          to be able to issue three syscalls by calling fixed addresses in
@@@ -2296,23 -2293,38 +2296,38 @@@
          it can be used to assist security vulnerability exploitation.
  
          This setting can be changed at boot time via the kernel command
-         line parameter vsyscall=[emulate|none].
+         line parameter vsyscall=[emulate|xonly|none].
  
          On a system with recent enough glibc (2.14 or newer) and no
          static binaries, you can say None without a performance penalty
          to improve security.
  
-         If unsure, select "Emulate".
+         If unsure, select "Emulate execution only".
  
        config LEGACY_VSYSCALL_EMULATE
-               bool "Emulate"
+               bool "Full emulation"
                help
-                 The kernel traps and emulates calls into the fixed
-                 vsyscall address mapping. This makes the mapping
-                 non-executable, but it still contains known contents,
-                 which could be used in certain rare security vulnerability
-                 exploits. This configuration is recommended when userspace
-                 still uses the vsyscall area.
+                 The kernel traps and emulates calls into the fixed vsyscall
+                 address mapping. This makes the mapping non-executable, but
+                 it still contains readable known contents, which could be
+                 used in certain rare security vulnerability exploits. This
+                 configuration is recommended when using legacy userspace
+                 that still uses vsyscalls along with legacy binary
+                 instrumentation tools that require code to be readable.
+ 
+                 An example of this type of legacy userspace is running
+                 Pin on an old binary that still uses vsyscalls.
+ 
+       config LEGACY_VSYSCALL_XONLY
+               bool "Emulate execution only"
+               help
+                 The kernel traps and emulates calls into the fixed vsyscall
+                 address mapping and does not allow reads.  This
+                 configuration is recommended when userspace might use the
+                 legacy vsyscall area but support for legacy binary
+                 instrumentation of legacy code is not needed.  It mitigates
+                 certain uses of the vsyscall area as an ASLR-bypassing
+                 buffer.
  
        config LEGACY_VSYSCALL_NONE
                bool "None"