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x86/selftests, x86/vm86: Improve entry_from_vm86 selftest
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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@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Denys Vlasenko <vda.linux@googlemail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Shuah Khan <shuahkh@osg.samsung.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/d8ef1d7368ac70d8342481563ed50f9a7d2eea6f.1436492057.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Andy Lutomirski authored and Ingo Molnar committed Jul 21, 2015
1 parent 5aef51c commit f2a50f8
Showing 1 changed file with 124 additions and 8 deletions.
132 changes: 124 additions & 8 deletions tools/testing/selftests/x86/entry_from_vm86.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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"
Expand All @@ -38,16 +87,26 @@ 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"
".popsection"
);

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;
Expand All @@ -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)
Expand All @@ -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);
}

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