[PATCH kvm-unit-tests 4/4] x86/taskswitch_vm86: Task switches into/out of VM86

[Kevin Wolf <kwolf@redhat.com>]

This adds a test case that jumps into VM86 by iret-ing to a TSS and back
to Protected Mode using a task gate in the IDT.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 config-i386.mak       |    3 +-
 lib/x86/desc.c        |   37 +-----------------------------
 lib/x86/desc.h        |   36 +++++++++++++++++++++++++++++
 lib/x86/vm.c          |    4 +-
 lib/x86/vm.h          |    1 +
 x86/taskswitch_vm86.c |   59 +++++++++++++++++++++++++++++++++++++++++++++++++
 x86/unittests.cfg     |    6 +++++
 7 files changed, 107 insertions(+), 39 deletions(-)
 create mode 100644 x86/taskswitch_vm86.c

diff --git a/config-i386.mak b/config-i386.mak
index de52f3d..b5c3b9c 100644
--- a/config-i386.mak
+++ b/config-i386.mak
@@ -5,9 +5,10 @@ ldarch = elf32-i386
 CFLAGS += -D__i386__
 CFLAGS += -I $(KERNELDIR)/include
 
-tests = $(TEST_DIR)/taskswitch.flat $(TEST_DIR)/taskswitch2.flat
+tests = $(TEST_DIR)/taskswitch.flat $(TEST_DIR)/taskswitch2.flat $(TEST_DIR)/taskswitch_vm86.flat
 
 include config-x86-common.mak
 
 $(TEST_DIR)/taskswitch.elf: $(cstart.o) $(TEST_DIR)/taskswitch.o
 $(TEST_DIR)/taskswitch2.elf: $(cstart.o) $(TEST_DIR)/taskswitch2.o
+$(TEST_DIR)/taskswitch_vm86.elf: $(cstart.o) $(TEST_DIR)/taskswitch_vm86.o
diff --git a/lib/x86/desc.c b/lib/x86/desc.c
index 770c250..c4a3607 100644
--- a/lib/x86/desc.c
+++ b/lib/x86/desc.c
@@ -27,41 +27,6 @@ typedef struct {
 	u8 base_high;
 } gdt_entry_t;
 
-typedef struct {
-	u16 prev;
-	u16 res1;
-	u32 esp0;
-	u16 ss0;
-	u16 res2;
-	u32 esp1;
-	u16 ss1;
-	u16 res3;
-	u32 esp2;
-	u16 ss2;
-	u16 res4;
-	u32 cr3;
-	u32 eip;
-	u32 eflags;
-	u32 eax, ecx, edx, ebx, esp, ebp, esi, edi;
-	u16 es;
-	u16 res5;
-	u16 cs;
-	u16 res6;
-	u16 ss;
-	u16 res7;
-	u16 ds;
-	u16 res8;
-	u16 fs;
-	u16 res9;
-	u16 gs;
-	u16 res10;
-	u16 ldt;
-	u16 res11;
-	u16 t:1;
-	u16 res12:15;
-	u16 iomap_base;
-} tss32_t;
-
 extern idt_entry_t boot_idt[256];
 
 void set_idt_entry(int vec, void *addr, int dpl)
@@ -327,7 +292,7 @@ void setup_gdt(void)
 		      ".Lflush2: "::"r"(0x10));
 }
 
-static void set_idt_task_gate(int vec, u16 sel)
+void set_idt_task_gate(int vec, u16 sel)
 {
     idt_entry_t *e = &boot_idt[vec];
 
diff --git a/lib/x86/desc.h b/lib/x86/desc.h
index 0b4897c..f819452 100644
--- a/lib/x86/desc.h
+++ b/lib/x86/desc.h
@@ -24,6 +24,41 @@ struct ex_regs {
     unsigned long rflags;
 };
 
+typedef struct {
+	u16 prev;
+	u16 res1;
+	u32 esp0;
+	u16 ss0;
+	u16 res2;
+	u32 esp1;
+	u16 ss1;
+	u16 res3;
+	u32 esp2;
+	u16 ss2;
+	u16 res4;
+	u32 cr3;
+	u32 eip;
+	u32 eflags;
+	u32 eax, ecx, edx, ebx, esp, ebp, esi, edi;
+	u16 es;
+	u16 res5;
+	u16 cs;
+	u16 res6;
+	u16 ss;
+	u16 res7;
+	u16 ds;
+	u16 res8;
+	u16 fs;
+	u16 res9;
+	u16 gs;
+	u16 res10;
+	u16 ldt;
+	u16 res11;
+	u16 t:1;
+	u16 res12:15;
+	u16 iomap_base;
+} tss32_t;
+
 #define ASM_TRY(catch)                                  \
     "movl $0, %%gs:4 \n\t"                              \
     ".pushsection .data.ex \n\t"                        \
@@ -44,6 +79,7 @@ unsigned exception_error_code(void);
 void set_idt_entry(int vec, void *addr, int dpl);
 void set_idt_sel(int vec, u16 sel);
 void set_gdt_entry(int num, u32 base,  u32 limit, u8 access, u8 gran);
+void set_idt_task_gate(int vec, u16 sel);
 void set_intr_task_gate(int e, void *fn);
 void print_current_tss_info(void);
 void handle_exception(u8 v, void (*func)(struct ex_regs *regs));
diff --git a/lib/x86/vm.c b/lib/x86/vm.c
index abbb0c9..aae044a 100644
--- a/lib/x86/vm.c
+++ b/lib/x86/vm.c
@@ -108,14 +108,14 @@ void install_large_page(unsigned long *cr3,
                               unsigned long phys,
                               void *virt)
 {
-    install_pte(cr3, 2, virt, phys | PTE_PRESENT | PTE_WRITE | PTE_PSE, 0);
+    install_pte(cr3, 2, virt, phys | PTE_PRESENT | PTE_WRITE | PTE_USER | PTE_PSE, 0);
 }
 
 void install_page(unsigned long *cr3,
                   unsigned long phys,
                   void *virt)
 {
-    install_pte(cr3, 1, virt, phys | PTE_PRESENT | PTE_WRITE, 0);
+    install_pte(cr3, 1, virt, phys | PTE_PRESENT | PTE_WRITE | PTE_USER, 0);
 }
 
 
diff --git a/lib/x86/vm.h b/lib/x86/vm.h
index bf8fd52..aebc5c3 100644
--- a/lib/x86/vm.h
+++ b/lib/x86/vm.h
@@ -13,6 +13,7 @@
 #define PTE_PRESENT (1ull << 0)
 #define PTE_PSE     (1ull << 7)
 #define PTE_WRITE   (1ull << 1)
+#define PTE_USER    (1ull << 2)
 #define PTE_ADDR    (0xffffffffff000ull)
 
 void setup_vm();
diff --git a/x86/taskswitch_vm86.c b/x86/taskswitch_vm86.c
new file mode 100644
index 0000000..363cb00
--- /dev/null
+++ b/x86/taskswitch_vm86.c
@@ -0,0 +1,59 @@
+#include "libcflat.h"
+#include "desc.h"
+#include "processor.h"
+#include "vm.h"
+
+static tss32_t main_tss;
+static tss32_t vm86_tss;
+
+#define FREE_GDT_INDEX 4
+#define MAIN_TSS_INDEX (FREE_GDT_INDEX + 0)
+#define VM86_TSS_INDEX (FREE_GDT_INDEX + 1)
+
+extern void vm86_start(void);
+
+int main(void)
+{
+    u8 *vm86_start;
+
+    setup_vm();
+    setup_idt();
+    setup_gdt();
+
+    /* Write a 'ud2' instruction somewhere below 1 MB */
+    vm86_start = (void*) 0x42000;
+    vm86_start[0] = 0x0f;
+    vm86_start[1] = 0x0b;
+
+    /* Main TSS */
+    set_gdt_entry(MAIN_TSS_INDEX, (u32)&main_tss, sizeof(tss32_t) - 1, 0x89, 0);
+    ltr(MAIN_TSS_INDEX << 3);
+    main_tss = (tss32_t) {
+        .prev   = VM86_TSS_INDEX << 3,
+        .cr3    = read_cr3(),
+    };
+
+    /* VM86 TSS (marked as busy, so we can iret to it) */
+    set_gdt_entry(VM86_TSS_INDEX, (u32)&vm86_tss, sizeof(tss32_t) - 1, 0x8b, 0);
+    vm86_tss = (tss32_t) {
+        .eflags = 0x20002,
+        .cr3    = read_cr3(),
+        .eip    = (u32) vm86_start & 0x0f,
+        .cs     = (u32) vm86_start >> 4,
+        .ds     = 0x1234,
+        .es     = 0x2345,
+    };
+
+    /* Setup task gate to main TSS for #UD */
+    set_idt_task_gate(6, MAIN_TSS_INDEX << 3);
+
+    /* Jump into VM86 task with iret, #UD lets it come back immediately */
+    asm volatile(
+        "pushf\n"
+        "orw $0x4000, (%esp)\n"
+        "popf\n"
+        "iret\n"
+    );
+
+    return 0;
+}
diff --git a/x86/unittests.cfg b/x86/unittests.cfg
index dac7d44..194850b 100644
--- a/x86/unittests.cfg
+++ b/x86/unittests.cfg
@@ -76,6 +76,12 @@ smp = 2
 extra_params = -cpu qemu64,-svm
 groups = task
 
+[taskswitch_vm86]
+file = taskswitch_vm86.flat
+smp = 2
+extra_params = -cpu qemu64,-svm
+groups = task
+
 [kvmclock_test]
 file = kvmclock_test.flat
 smp = 2
-- 
1.7.6.5