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Subject[PATCH 24/30] x86, kaiser: disable native VSYSCALL
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From: Dave Hansen <dave.hansen@linux.intel.com>

The VSYSCALL page is mapped by kernel page tables at a kernel address.
It is troublesome to support with KAISER in place, so disable the
native case.

Also add some help text about how KAISER might affect the emulation
case as well.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Moritz Lipp <moritz.lipp@iaik.tugraz.at>
Cc: Daniel Gruss <daniel.gruss@iaik.tugraz.at>
Cc: Michael Schwarz <michael.schwarz@iaik.tugraz.at>
Cc: Richard Fellner <richard.fellner@student.tugraz.at>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Kees Cook <keescook@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: x86@kernel.org

---

b/arch/x86/Kconfig | 8 ++++++++
1 file changed, 8 insertions(+)

diff -puN arch/x86/Kconfig~kaiser-no-vsyscall arch/x86/Kconfig
--- a/arch/x86/Kconfig~kaiser-no-vsyscall 2017-11-08 10:45:39.157681370 -0800
+++ b/arch/x86/Kconfig 2017-11-08 10:45:39.162681370 -0800
@@ -2231,6 +2231,9 @@ choice

config LEGACY_VSYSCALL_NATIVE
bool "Native"
+ # The VSYSCALL page comes from the kernel page tables
+ # and is not available when KAISER is enabled.
+ depends on ! KAISER
help
Actual executable code is located in the fixed vsyscall
address mapping, implementing time() efficiently. Since
@@ -2248,6 +2251,11 @@ choice
exploits. This configuration is recommended when userspace
still uses the vsyscall area.

+ When KAISER is enabled, the vsyscall area will become
+ unreadable. This emulation option still works, but KAISER
+ will make it harder to do things like trace code using the
+ emulation.
+
config LEGACY_VSYSCALL_NONE
bool "None"
help
_
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