[PATCH kvm-unit-tests] x86: Test rflags.rf is set upon faults

[Nadav Amit]

This patch tests whether rflags.rf is set upon #UD and #GP faults as it should,
according to Intel SDM 17.3.1.1.  The patch saves rflags.rf in an unused bit of
the value which is saved during exception handling to save rflags.rf.

Signed-off-by: Nadav Amit <namit@xxxxxxxxxxxxxxxxx>
---
 lib/x86/desc.c | 16 ++++++++++++----
 lib/x86/desc.h |  1 +
 x86/idt_test.c | 13 +++++++++----
 3 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/lib/x86/desc.c b/lib/x86/desc.c
index 9a80f48..7fbe774 100644
--- a/lib/x86/desc.c
+++ b/lib/x86/desc.c
@@ -36,8 +36,8 @@ static void check_exception_table(struct ex_regs *regs)
     struct ex_record *ex;
     unsigned ex_val;
 
-    ex_val = regs->vector | (regs->error_code << 16);
-
+    ex_val = regs->vector | (regs->error_code << 16) |
+		(((regs->rflags >> 16) & 1) << 8);
     asm("mov %0, %%gs:4" : : "r"(ex_val));
 
     for (ex = &exception_table_start; ex != &exception_table_end; ++ex) {
@@ -173,9 +173,9 @@ void setup_idt(void)
 
 unsigned exception_vector(void)
 {
-    unsigned short vector;
+    unsigned char vector;
 
-    asm("mov %%gs:4, %0" : "=rm"(vector));
+    asm("movb %%gs:4, %0" : "=q"(vector));
     return vector;
 }
 
@@ -187,6 +187,14 @@ unsigned exception_error_code(void)
     return error_code;
 }
 
+bool exception_rflags_rf(void)
+{
+    unsigned char rf_flag;
+
+    asm("movb %%gs:5, %b0" : "=q"(rf_flag));
+    return rf_flag & 1;
+}
+
 static char intr_alt_stack[4096];
 
 #ifndef __x86_64__
diff --git a/lib/x86/desc.h b/lib/x86/desc.h
index 553bce9..bd4293e 100644
--- a/lib/x86/desc.h
+++ b/lib/x86/desc.h
@@ -144,6 +144,7 @@ extern tss64_t tss;
 
 unsigned exception_vector(void);
 unsigned exception_error_code(void);
+bool exception_rflags_rf(void);
 void set_idt_entry(int vec, void *addr, int dpl);
 void set_idt_sel(int vec, u16 sel);
 void set_gdt_entry(int sel, u32 base,  u32 limit, u8 access, u8 gran);
diff --git a/x86/idt_test.c b/x86/idt_test.c
index ecb76bb..349aade 100644
--- a/x86/idt_test.c
+++ b/x86/idt_test.c
@@ -1,15 +1,16 @@
 #include "libcflat.h"
 #include "desc.h"
 
-int test_ud2(void)
+int test_ud2(bool *rflags_rf)
 {
     asm volatile(ASM_TRY("1f")
                  "ud2 \n\t"
                  "1:" :);
+    *rflags_rf = exception_rflags_rf();
     return exception_vector();
 }
 
-int test_gp(void)
+int test_gp(bool *rflags_rf)
 {
     unsigned long tmp;
 
@@ -18,19 +19,23 @@ int test_gp(void)
 		 "mov %0, %%cr4\n\t"
                  "1:"
                  : "=a"(tmp));
+    *rflags_rf = exception_rflags_rf();
     return exception_vector();
 }
 
 int main(void)
 {
     int r;
+    bool rflags_rf;
 
     printf("Starting IDT test\n");
     setup_idt();
-    r = test_gp();
+    r = test_gp(&rflags_rf);
     report("Testing #GP", r == GP_VECTOR);
-    r = test_ud2();
+    report("Testing #GP rflags.rf", rflags_rf);
+    r = test_ud2(&rflags_rf);
     report("Testing #UD", r == UD_VECTOR);
+    report("Testing #UD rflags.rf", rflags_rf);
 
     return report_summary();
 }
-- 
1.9.1

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