Re: [RFC/PATCH v2 v2 1/6] x86/selftests, x86/vm86: Improve entry_from_vm86 selftest

[Andy Lutomirski]

Ingo, would it make sense for you to apply just this patch?  It should
be helpful for testing whatever we end up doing with the vm86 code.

Thanks,
Andy

On Thu, Jul 9, 2015 at 7:17 PM, Andy Lutomirski <luto@xxxxxxxxxx> wrote:
> The entry_from_vm86 selftest was very weak.  Improve it: test more
> types of kernel entries from vm86 mode and test them more carefully.
>
> While we're at it, try to improve behavior on non-SEP CPUs.  The
> old code was buggy because I misunderstood the intended semantics
> of #UD in vm86, so I didn't handle a possible signal.
>
> Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
> ---
>  tools/testing/selftests/x86/entry_from_vm86.c | 132 ++++++++++++++++++++++++--
>  1 file changed, 124 insertions(+), 8 deletions(-)
>
> diff --git a/tools/testing/selftests/x86/entry_from_vm86.c b/tools/testing/selftests/x86/entry_from_vm86.c
> index 5c38a187677b..f004b2a09916 100644
> --- a/tools/testing/selftests/x86/entry_from_vm86.c
> +++ b/tools/testing/selftests/x86/entry_from_vm86.c
> @@ -28,6 +28,55 @@
>  static unsigned long load_addr = 0x10000;
>  static int nerrs = 0;
>
> +static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
> +                      int flags)
> +{
> +       struct sigaction sa;
> +       memset(&sa, 0, sizeof(sa));
> +       sa.sa_sigaction = handler;
> +       sa.sa_flags = SA_SIGINFO | flags;
> +       sigemptyset(&sa.sa_mask);
> +       if (sigaction(sig, &sa, 0))
> +               err(1, "sigaction");
> +}
> +
> +static void clearhandler(int sig)
> +{
> +       struct sigaction sa;
> +       memset(&sa, 0, sizeof(sa));
> +       sa.sa_handler = SIG_DFL;
> +       sigemptyset(&sa.sa_mask);
> +       if (sigaction(sig, &sa, 0))
> +               err(1, "sigaction");
> +}
> +
> +static sig_atomic_t got_signal;
> +
> +static void sighandler(int sig, siginfo_t *info, void *ctx_void)
> +{
> +       ucontext_t *ctx = (ucontext_t*)ctx_void;
> +
> +       if (ctx->uc_mcontext.gregs[REG_EFL] & X86_EFLAGS_VM ||
> +           (ctx->uc_mcontext.gregs[REG_CS] & 3) != 3) {
> +               printf("[FAIL]\tSignal frame should not reflect vm86 mode\n");
> +               nerrs++;
> +       }
> +
> +       const char *signame;
> +       if (sig == SIGSEGV)
> +               signame = "SIGSEGV";
> +       else if (sig == SIGILL)
> +               signame = "SIGILL";
> +       else
> +               signame = "unexpected signal";
> +
> +       printf("[INFO]\t%s: FLAGS = 0x%lx, CS = 0x%hx\n", signame,
> +              (unsigned long)ctx->uc_mcontext.gregs[REG_EFL],
> +              (unsigned short)ctx->uc_mcontext.gregs[REG_CS]);
> +
> +       got_signal = 1;
> +}
> +
>  asm (
>         ".pushsection .rodata\n\t"
>         ".type vmcode_bound, @object\n\t"
> @@ -38,6 +87,14 @@ asm (
>         "int3\n\t"
>         "vmcode_sysenter:\n\t"
>         "sysenter\n\t"
> +       "vmcode_syscall:\n\t"
> +       "syscall\n\t"
> +       "vmcode_sti:\n\t"
> +       "sti\n\t"
> +       "vmcode_int3:\n\t"
> +       "int3\n\t"
> +       "vmcode_int80:\n\t"
> +       "int $0x80\n\t"
>         ".size vmcode, . - vmcode\n\t"
>         "end_vmcode:\n\t"
>         ".code32\n\t"
> @@ -45,9 +102,11 @@ asm (
>         );
>
>  extern unsigned char vmcode[], end_vmcode[];
> -extern unsigned char vmcode_bound[], vmcode_sysenter[];
> +extern unsigned char vmcode_bound[], vmcode_sysenter[], vmcode_syscall[],
> +       vmcode_sti[], vmcode_int3[], vmcode_int80[];
>
>  static void do_test(struct vm86plus_struct *v86, unsigned long eip,
> +                   unsigned int rettype, unsigned int retarg,
>                     const char *text)
>  {
>         long ret;
> @@ -73,13 +132,28 @@ static void do_test(struct vm86plus_struct *v86, unsigned long eip,
>                 else
>                         sprintf(trapname, "%d", trapno);
>
> -               printf("[OK]\tExited vm86 mode due to #%s\n", trapname);
> +               printf("[INFO]\tExited vm86 mode due to #%s\n", trapname);
>         } else if (VM86_TYPE(ret) == VM86_UNKNOWN) {
> -               printf("[OK]\tExited vm86 mode due to unhandled GP fault\n");
> +               printf("[INFO]\tExited vm86 mode due to unhandled GP fault\n");
> +       } else if (VM86_TYPE(ret) == VM86_TRAP) {
> +               printf("[INFO]\tExited vm86 mode due to a trap (arg=%ld)\n",
> +                      VM86_ARG(ret));
> +       } else if (VM86_TYPE(ret) == VM86_SIGNAL) {
> +               printf("[INFO]\tExited vm86 mode due to a signal\n");
> +       } else if (VM86_TYPE(ret) == VM86_STI) {
> +               printf("[INFO]\tExited vm86 mode due to STI\n");
>         } else {
> -               printf("[OK]\tExited vm86 mode due to type %ld, arg %ld\n",
> +               printf("[INFO]\tExited vm86 mode due to type %ld, arg %ld\n",
>                        VM86_TYPE(ret), VM86_ARG(ret));
>         }
> +
> +       if (rettype == -1 ||
> +           (VM86_TYPE(ret) == rettype && VM86_ARG(ret) == retarg)) {
> +               printf("[OK]\tReturned correctly\n");
> +       } else {
> +               printf("[FAIL]\tIncorrect return reason\n");
> +               nerrs++;
> +       }
>  }
>
>  int main(void)
> @@ -105,10 +179,52 @@ int main(void)
>         assert((v86.regs.cs & 3) == 0); /* Looks like RPL = 0 */
>
>         /* #BR -- should deliver SIG??? */
> -       do_test(&v86, vmcode_bound - vmcode, "#BR");
> -
> -       /* SYSENTER -- should cause #GP or #UD depending on CPU */
> -       do_test(&v86, vmcode_sysenter - vmcode, "SYSENTER");
> +       do_test(&v86, vmcode_bound - vmcode, VM86_INTx, 5, "#BR");
> +
> +       /*
> +        * SYSENTER -- should cause #GP or #UD depending on CPU.
> +        * Expected return type -1 means that we shouldn't validate
> +        * the vm86 return value.  This will avoid problems on non-SEP
> +        * CPUs.
> +        */
> +       sethandler(SIGILL, sighandler, 0);
> +       do_test(&v86, vmcode_sysenter - vmcode, -1, 0, "SYSENTER");
> +       clearhandler(SIGILL);
> +
> +       /*
> +        * SYSCALL would be a disaster in VM86 mode.  Fortunately,
> +        * there is no kernel that both enables SYSCALL and sets
> +        * EFER.SCE, so it's #UD on all systems.  But vm86 is
> +        * buggy (or has a "feature"), so the SIGILL will actually
> +        * be delivered.
> +        */
> +       sethandler(SIGILL, sighandler, 0);
> +       do_test(&v86, vmcode_syscall - vmcode, VM86_SIGNAL, 0, "SYSCALL");
> +       clearhandler(SIGILL);
> +
> +       /* STI with VIP set */
> +       v86.regs.eflags |= X86_EFLAGS_VIP;
> +       v86.regs.eflags &= ~X86_EFLAGS_IF;
> +       do_test(&v86, vmcode_sti - vmcode, VM86_STI, 0, "STI with VIP set");
> +
> +       /* INT3 -- should cause #BP */
> +       do_test(&v86, vmcode_int3 - vmcode, VM86_TRAP, 3, "INT3");
> +
> +       /* INT80 -- should exit with "INTx 0x80" */
> +       v86.regs.eax = (unsigned int)-1;
> +       do_test(&v86, vmcode_int80 - vmcode, VM86_INTx, 0x80, "int80");
> +
> +       /* Execute a null pointer */
> +       v86.regs.cs = 0;
> +       v86.regs.ss = 0;
> +       sethandler(SIGSEGV, sighandler, 0);
> +       got_signal = 0;
> +       do_test(&v86, 0, VM86_SIGNAL, 0, "Execute null pointer");
> +       if (!got_signal) {
> +               printf("[FAIL]\tDid not receive SIGSEGV\n");
> +               nerrs++;
> +       }
> +       clearhandler(SIGSEGV);
>
>         return (nerrs == 0 ? 0 : 1);
>  }
> --
> 2.4.3
>



-- 
Andy Lutomirski
AMA Capital Management, LLC
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/