x86: Add a new test case for ret/iret with a nullified segment
This makes up the test case for the following QEMU patch:
http://patchwork.ozlabs.org/project/qemu-devel/patch/1605261378-77971-1-git-send-email-bmeng.cn@gmail.com/
Note the test case only fails on an unpatched QEMU with "accel=tcg".
Signed-off-by: Bin Meng <bin.meng@windriver.com>
Message-Id: <1606206780-80123-1-git-send-email-bmeng.cn@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/x86/emulator.c b/x86/emulator.c
index e46d97e..6100b6d 100644
--- a/x86/emulator.c
+++ b/x86/emulator.c
@@ -6,10 +6,14 @@
#include "processor.h"
#include "vmalloc.h"
#include "alloc_page.h"
+#include "usermode.h"
#define memset __builtin_memset
#define TESTDEV_IO_PORT 0xe0
+#define MAGIC_NUM 0xdeadbeefdeadbeefUL
+#define GS_BASE 0x400000
+
static int exceptions;
/* Forced emulation prefix, used to invoke the emulator unconditionally. */
@@ -925,6 +929,39 @@
write_ss(ss);
}
+static uint64_t usr_gs_mov(void)
+{
+ static uint64_t dummy = MAGIC_NUM;
+ uint64_t dummy_ptr = (uint64_t)&dummy;
+ uint64_t ret;
+
+ dummy_ptr -= GS_BASE;
+ asm volatile("mov %%gs:(%%rcx), %%rax" : "=a"(ret): "c"(dummy_ptr) :);
+
+ return ret;
+}
+
+static void test_iret(void)
+{
+ uint64_t val;
+ bool raised_vector;
+
+ /* Update GS base to 4MiB */
+ wrmsr(MSR_GS_BASE, GS_BASE);
+
+ /*
+ * Per the SDM, jumping to user mode via `iret`, which is returning to
+ * outer privilege level, for segment registers (ES, FS, GS, and DS)
+ * if the check fails, the segment selector becomes null.
+ *
+ * In our test case, GS becomes null.
+ */
+ val = run_in_user((usermode_func)usr_gs_mov, GP_VECTOR,
+ 0, 0, 0, 0, &raised_vector);
+
+ report(val == MAGIC_NUM, "Test ret/iret with a nullified segment");
+}
+
/* Broken emulation causes triple fault, which skips the other tests. */
#if 0
static void test_lldt(volatile uint16_t *mem)
@@ -1074,6 +1111,7 @@
test_shld_shrd(mem);
//test_lgdt_lidt(mem);
test_sreg(mem);
+ test_iret();
//test_lldt(mem);
test_ltr(mem);
test_cmov(mem);
