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

Yu-cheng Yu
2019-08-13T21:04:19Z

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