linux-kernel - [PATCH v12 8/8] x86: Disallow vsyscall emulation when CET is enabled

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Message-Id: <20200918192312.25978-9-yu-cheng.yu@intel.com>
Date:   Fri, 18 Sep 2020 12:23:12 -0700
From:   Yu-cheng Yu <yu-cheng.yu@...el.com>
To:     x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Balbir Singh <bsingharora@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>,
        Dave Martin <Dave.Martin@....com>,
        Weijiang Yang <weijiang.yang@...el.com>
Cc:     Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: [PATCH v12 8/8] x86: Disallow vsyscall emulation when CET is enabled

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

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
---
v12:
- Disable vsyscall emulation only when it is attempted (vs. at compile time).

 arch/x86/entry/vsyscall/vsyscall_64.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c
index 44c33103a955..3196e963e365 100644
--- a/arch/x86/entry/vsyscall/vsyscall_64.c
+++ b/arch/x86/entry/vsyscall/vsyscall_64.c
@@ -150,6 +150,15 @@ bool emulate_vsyscall(unsigned long error_code,
 
 	WARN_ON_ONCE(address != regs->ip);
 
+#ifdef CONFIG_X86_INTEL_CET
+	if (current->thread.cet.shstk_size ||
+	    current->thread.cet.ibt_enabled) {
+		warn_bad_vsyscall(KERN_INFO, regs,
+				  "vsyscall attempted with cet enabled");
+		return false;
+	}
+#endif
+
 	if (vsyscall_mode == NONE) {
 		warn_bad_vsyscall(KERN_INFO, regs,
 				  "vsyscall attempted with vsyscall=none");
-- 
2.21.0