selftests/x86/entry_from_vm86: Add test cases for POPF

POPF is currently broken -- add tests to catch the error.  This
results in:

   [RUN]	POPF with VIP set and IF clear from vm86 mode
   [INFO]	Exited vm86 mode due to STI
   [FAIL]	Incorrect return reason (started at eip = 0xd, ended at eip = 0xf)

because POPF currently fails to check IF before reporting a pending
interrupt.

This patch also makes the FAIL message a bit more informative.

Reported-by: Bart Oldeman <bartoldeman@gmail.com>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stas Sergeev <stsp@list.ru>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/a16270b5cfe7832d6d00c479d0f871066cbdb52b.1521003603.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 27 insertions, 3 deletions

diff --git a/tools/testing/selftests/x86/entry_from_vm86.c b/tools/testing/selftests/x86/entry_from_vm86.c
index 6e85f0d0498d..ade443a88421 100644
--- a/tools/testing/selftests/x86/entry_from_vm86.c
+++ b/tools/testing/selftests/x86/entry_from_vm86.c
@@ -95,6 +95,10 @@ asm (
         "int3\n\t"
         "vmcode_int80:\n\t"
         "int $0x80\n\t"
+        "vmcode_popf_hlt:\n\t"
+        "push %ax\n\t"
+        "popf\n\t"
+        "hlt\n\t"
         "vmcode_umip:\n\t"
         /* addressing via displacements */
         "smsw (2052)\n\t"
@@ -124,8 +128,8 @@ asm (
 
 extern unsigned char vmcode[], end_vmcode[];
 extern unsigned char vmcode_bound[], vmcode_sysenter[], vmcode_syscall[],
-        vmcode_sti[], vmcode_int3[], vmcode_int80[], vmcode_umip[],
-        vmcode_umip_str[], vmcode_umip_sldt[];
+        vmcode_sti[], vmcode_int3[], vmcode_int80[], vmcode_popf_hlt[],
+        vmcode_umip[], vmcode_umip_str[], vmcode_umip_sldt[];
 
 /* Returns false if the test was skipped. */
 static bool do_test(struct vm86plus_struct *v86, unsigned long eip,
@@ -175,7 +179,7 @@ static bool do_test(struct vm86plus_struct *v86, unsigned long eip,
             (VM86_TYPE(ret) == rettype && VM86_ARG(ret) == retarg)) {
                 printf("[OK]\tReturned correctly\n");
         } else {
-                printf("[FAIL]\tIncorrect return reason\n");
+                printf("[FAIL]\tIncorrect return reason (started at eip = 0x%lx, ended at eip = 0x%lx)\n", eip, v86->regs.eip);
                 nerrs++;
         }
 
@@ -264,6 +268,9 @@ int main(void)
         v86.regs.ds = load_addr / 16;
         v86.regs.es = load_addr / 16;
 
+        /* Use the end of the page as our stack. */
+        v86.regs.esp = 4096;
+
         assert((v86.regs.cs & 3) == 0); /* Looks like RPL = 0 */
 
         /* #BR -- should deliver SIG??? */
@@ -295,6 +302,23 @@ int main(void)
         v86.regs.eflags &= ~X86_EFLAGS_IF;
         do_test(&v86, vmcode_sti - vmcode, VM86_STI, 0, "STI with VIP set");
 
+        /* POPF with VIP set but IF clear: should not trap */
+        v86.regs.eflags = X86_EFLAGS_VIP;
+        v86.regs.eax = 0;
+        do_test(&v86, vmcode_popf_hlt - vmcode, VM86_UNKNOWN, 0, "POPF with VIP set and IF clear");
+
+        /* POPF with VIP set and IF set: should trap */
+        v86.regs.eflags = X86_EFLAGS_VIP;
+        v86.regs.eax = X86_EFLAGS_IF;
+        do_test(&v86, vmcode_popf_hlt - vmcode, VM86_STI, 0, "POPF with VIP and IF set");
+
+        /* POPF with VIP clear and IF set: should not trap */
+        v86.regs.eflags = 0;
+        v86.regs.eax = X86_EFLAGS_IF;
+        do_test(&v86, vmcode_popf_hlt - vmcode, VM86_UNKNOWN, 0, "POPF with VIP clear and IF set");
+
+        v86.regs.eflags = 0;
+
         /* INT3 -- should cause #BP */
         do_test(&v86, vmcode_int3 - vmcode, VM86_TRAP, 3, "INT3");