linux-kernel - [PATCH v8 11/14] x86/vsyscall/64: Fixup shadow stack and branch tracking for vsyscall

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Message-Id: <20190813205359.12196-12-yu-cheng.yu@intel.com>
Date:   Tue, 13 Aug 2019 13:53:56 -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@...capital.net>,
        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>
Cc:     Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: [PATCH v8 11/14] x86/vsyscall/64: Fixup shadow stack and branch tracking for vsyscall

When emulating a RET, also unwind the task's shadow stack and cancel
the current branch tracking status.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
---
 arch/x86/entry/vsyscall/vsyscall_64.c    | 29 ++++++++++++++++++++++++
 arch/x86/entry/vsyscall/vsyscall_trace.h |  1 +
 2 files changed, 30 insertions(+)

diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c
index e7c596dea947..27ff81f75c82 100644
--- a/arch/x86/entry/vsyscall/vsyscall_64.c
+++ b/arch/x86/entry/vsyscall/vsyscall_64.c
@@ -38,6 +38,9 @@
 #include <asm/fixmap.h>
 #include <asm/traps.h>
 #include <asm/paravirt.h>
+#include <asm/fpu/xstate.h>
+#include <asm/fpu/types.h>
+#include <asm/fpu/internal.h>
 
 #define CREATE_TRACE_POINTS
 #include "vsyscall_trace.h"
@@ -286,6 +289,32 @@ bool emulate_vsyscall(unsigned long error_code,
 	/* Emulate a ret instruction. */
 	regs->ip = caller;
 	regs->sp += 8;
+
+	/* Unwind shadow stack. */
+
+#ifdef CONFIG_X86_INTEL_SHADOW_STACK_USER
+	if (current->thread.cet.shstk_enabled) {
+		u64 r;
+
+		modify_fpu_regs_begin();
+		rdmsrl(MSR_IA32_PL3_SSP, r);
+		wrmsrl(MSR_IA32_PL3_SSP, r + 8);
+		modify_fpu_regs_end();
+	}
+#endif
+
+	/* Fixup branch tracking */
+#ifdef CONFIG_X86_INTEL_BRANCH_TRACKING_USER
+	if (current->thread.cet.ibt_enabled) {
+		u64 r;
+
+		modify_fpu_regs_begin();
+		rdmsrl(MSR_IA32_U_CET, r);
+		wrmsrl(MSR_IA32_U_CET, r & ~MSR_IA32_CET_WAIT_ENDBR);
+		modify_fpu_regs_end();
+	}
+#endif
+
 	return true;
 
 sigsegv:
diff --git a/arch/x86/entry/vsyscall/vsyscall_trace.h b/arch/x86/entry/vsyscall/vsyscall_trace.h
index 3c3f9765a85c..7aa2101ada44 100644
--- a/arch/x86/entry/vsyscall/vsyscall_trace.h
+++ b/arch/x86/entry/vsyscall/vsyscall_trace.h
@@ -25,6 +25,7 @@ TRACE_EVENT(emulate_vsyscall,
 #endif
 
 #undef TRACE_INCLUDE_PATH
+#undef TRACE_INCLUDE_FILE
 #define TRACE_INCLUDE_PATH ../../arch/x86/entry/vsyscall/
 #define TRACE_INCLUDE_FILE vsyscall_trace
 #include <trace/define_trace.h>
-- 
2.17.1