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Subject[PATCH v11 9/9] x86: Disallow vsyscall emulation when CET is enabled
Date
From: "H.J. Lu" <hjl.tools@gmail.com>

Emulation of the legacy vsyscall page is required by some programs built
before 2013. Newer programs after 2013 don't use it. Disallow vsyscall
emulation when Control-flow Enforcement (CET) is enabled to enhance
security.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
---
arch/x86/Kconfig | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 5bd6d6a10047..bbc68ecfae2b 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1210,7 +1210,7 @@ config X86_ESPFIX64
config X86_VSYSCALL_EMULATION
bool "Enable vsyscall emulation" if EXPERT
default y
- depends on X86_64
+ depends on X86_64 && !X86_INTEL_CET
help
This enables emulation of the legacy vsyscall page. Disabling
it is roughly equivalent to booting with vsyscall=none, except
@@ -1225,6 +1225,8 @@ config X86_VSYSCALL_EMULATION
Disabling this option saves about 7K of kernel size and
possibly 4K of additional runtime pagetable memory.

+ This option is disabled when Intel CET is enabled.
+
config X86_IOPL_IOPERM
bool "IOPERM and IOPL Emulation"
default y
@@ -2361,7 +2363,7 @@ config COMPAT_VDSO

choice
prompt "vsyscall table for legacy applications"
- depends on X86_64
+ depends on X86_64 && !X86_INTEL_CET
default LEGACY_VSYSCALL_XONLY
help
Legacy user code that does not know how to find the vDSO expects
@@ -2378,6 +2380,8 @@ choice

If unsure, select "Emulate execution only".

+ This option is not enabled when Intel CET is enabled.
+
config LEGACY_VSYSCALL_EMULATE
bool "Full emulation"
help
--
2.21.0
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