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From:   Yu-cheng Yu <yu-cheng.yu@intel.com>
To:     x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
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        Dave Hansen <dave.hansen@linux.intel.com>,
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Cc:     Yu-cheng Yu <yu-cheng.yu@intel.com>
Subject: [PATCH v11 9/9] x86: Disallow vsyscall emulation when CET is enabled
Date:   Mon, 24 Aug 2020 17:26:44 -0700
Message-Id: <20200825002645.3658-10-yu-cheng.yu@intel.com>
In-Reply-To: <20200825002645.3658-1-yu-cheng.yu@intel.com>
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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