[PATCH kvm-unit-tests v2 1/3] VMX: move write_rflags inside asm blocks for vmx instructions

[Bandan Das <bsd@xxxxxxxxxx>]

This makes sure that the flags register doesn't get accidentally
overwritten due to compiler optimizations or other means

Signed-off-by: Bandan Das <bsd@xxxxxxxxxx>
---
 lib/x86/processor.h |  7 -------
 x86/vmx.c           | 31 ++++++++++---------------------
 x86/vmx.h           | 10 ++++++++--
 3 files changed, 18 insertions(+), 30 deletions(-)

diff --git a/lib/x86/processor.h b/lib/x86/processor.h
index 7fc1026..f5f1c82 100644
--- a/lib/x86/processor.h
+++ b/lib/x86/processor.h
@@ -351,11 +351,4 @@ static inline void safe_halt(void)
 	asm volatile("sti; hlt");
 }
 
-#ifdef __x86_64__
-static inline void write_rflags(u64 r)
-{
-	asm volatile("push %0; popf\n\t" : : "q"(r) : "cc");
-}
-#endif
-
 #endif
diff --git a/x86/vmx.c b/x86/vmx.c
index 1182eef..768d07f 100644
--- a/x86/vmx.c
+++ b/x86/vmx.c
@@ -65,8 +65,10 @@ extern void *guest_entry;
 static int make_vmcs_current(struct vmcs *vmcs)
 {
 	bool ret;
+	u64 rflags = read_rflags() | X86_EFLAGS_CF | X86_EFLAGS_ZF;
 
-	asm volatile ("vmptrld %1; setbe %0" : "=q" (ret) : "m" (vmcs) : "cc");
+	asm volatile ("push %1; popf; vmptrld %2; setbe %0"
+		      : "=q" (ret) : "q" (rflags), "m" (vmcs) : "cc");
 	return ret;
 }
 
@@ -92,16 +94,19 @@ static void __attribute__((__used__)) syscall_handler(u64 syscall_no)
 static inline int vmx_on()
 {
 	bool ret;
-	asm volatile ("vmxon %1; setbe %0\n\t"
-		: "=q"(ret) : "m"(vmxon_region) : "cc");
+	u64 rflags = read_rflags() | X86_EFLAGS_CF | X86_EFLAGS_ZF;
+	asm volatile ("push %1; popf; vmxon %2; setbe %0\n\t"
+		      : "=q" (ret) : "q" (rflags), "m" (vmxon_region) : "cc");
 	return ret;
 }
 
 static inline int vmx_off()
 {
 	bool ret;
-	asm volatile("vmxoff; setbe %0\n\t"
-		: "=q"(ret) : : "cc");
+	u64 rflags = read_rflags() | X86_EFLAGS_CF | X86_EFLAGS_ZF;
+
+	asm volatile("push %1; popf; vmxoff; setbe %0\n\t"
+		     : "=q"(ret) : "q" (rflags) : "cc");
 	return ret;
 }
 
@@ -129,20 +134,13 @@ void print_vmexit_info()
 
 static void test_vmclear(void)
 {
-	u64 rflags;
-
-	rflags = read_rflags() | X86_EFLAGS_CF | X86_EFLAGS_ZF;
-	write_rflags(rflags);
 	report("test vmclear", vmcs_clear(vmcs_root) == 0);
 }
 
 static void test_vmxoff(void)
 {
 	int ret;
-	u64 rflags;
 
-	rflags = read_rflags() | X86_EFLAGS_CF | X86_EFLAGS_ZF;
-	write_rflags(rflags);
 	ret = vmx_off();
 	report("test vmxoff", !ret);
 }
@@ -599,10 +597,7 @@ static int test_vmx_feature_control(void)
 static int test_vmxon(void)
 {
 	int ret;
-	u64 rflags;
 
-	rflags = read_rflags() | X86_EFLAGS_CF | X86_EFLAGS_ZF;
-	write_rflags(rflags);
 	ret = vmx_on();
 	report("test vmxon", !ret);
 	return ret;
@@ -610,27 +605,21 @@ static int test_vmxon(void)
 
 static void test_vmptrld(void)
 {
-	u64 rflags;
 	struct vmcs *vmcs;
 
 	vmcs = alloc_page();
 	vmcs->revision_id = basic.revision;
-	rflags = read_rflags() | X86_EFLAGS_CF | X86_EFLAGS_ZF;
-	write_rflags(rflags);
 	report("test vmptrld", make_vmcs_current(vmcs) == 0);
 }
 
 static void test_vmptrst(void)
 {
-	u64 rflags;
 	int ret;
 	struct vmcs *vmcs1, *vmcs2;
 
 	vmcs1 = alloc_page();
 	memset(vmcs1, 0, PAGE_SIZE);
 	init_vmcs(&vmcs1);
-	rflags = read_rflags() | X86_EFLAGS_CF | X86_EFLAGS_ZF;
-	write_rflags(rflags);
 	ret = vmcs_save(&vmcs2);
 	report("test vmptrst", (!ret) && (vmcs1 == vmcs2));
 }
diff --git a/x86/vmx.h b/x86/vmx.h
index 26dd161..86bdf67 100644
--- a/x86/vmx.h
+++ b/x86/vmx.h
@@ -2,6 +2,7 @@
 #define __VMX_H
 
 #include "libcflat.h"
+#include "processor.h"
 
 struct vmcs {
 	u32 revision_id; /* vmcs revision identifier */
@@ -515,7 +516,10 @@ extern union vmx_ept_vpid  ept_vpid;
 static inline int vmcs_clear(struct vmcs *vmcs)
 {
 	bool ret;
-	asm volatile ("vmclear %1; setbe %0" : "=q" (ret) : "m" (vmcs) : "cc");
+	u64 rflags = read_rflags() | X86_EFLAGS_CF | X86_EFLAGS_ZF;
+
+	asm volatile ("push %1; popf; vmclear %2; setbe %0"
+		      : "=q" (ret) : "q" (rflags), "m" (vmcs) : "cc");
 	return ret;
 }
 
@@ -537,8 +541,10 @@ static inline int vmcs_write(enum Encoding enc, u64 val)
 static inline int vmcs_save(struct vmcs **vmcs)
 {
 	bool ret;
+	u64 rflags = read_rflags() | X86_EFLAGS_CF | X86_EFLAGS_ZF;
 
-	asm volatile ("vmptrst %1; setbe %0" : "=q" (ret) : "m" (*vmcs) : "cc");
+	asm volatile ("push %1; popf; vmptrst %2; setbe %0"
+		      : "=q" (ret) : "q" (rflags), "m" (*vmcs) : "cc");
 	return ret;
 }
 
-- 
1.8.3.1

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