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

From: Yu-cheng Yu <yu-cheng.yu@intel.com>
To: x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
	linux-mm@kvack.org, linux-arch@vger.kernel.org,
	linux-api@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
	Andy Lutomirski <luto@amacapital.net>,
	Balbir Singh <bsingharora@gmail.com>,
	Borislav Petkov <bp@alien8.de>,
	Cyrill Gorcunov <gorcunov@gmail.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Eugene Syromiatnikov <esyr@redhat.com>,
	Florian Weimer <fweimer@redhat.com>,
	"H.J. Lu" <hjl.tools@gmail.com>, Jann Horn <jannh@google.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Kees Cook <keescook@chromium.org>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Nadav Amit <nadav.amit@gmail.com>
Cc: Yu-cheng Yu <yu-cheng.yu@intel.com>
Subject: [PATCH v8 11/14] x86/vsyscall/64: Fixup shadow stack and branch tracking for vsyscall
Date: Tue, 13 Aug 2019 13:53:56 -0700	[thread overview]
Message-ID: <20190813205359.12196-12-yu-cheng.yu@intel.com> (raw)
In-Reply-To: <20190813205359.12196-1-yu-cheng.yu@intel.com>

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@intel.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
