x86/selftests/pkeys: Fork() to check for state being preserved

There was a bug where the per-mm pkey state was not being preserved across
fork() in the child.  fork() is performed in the pkey selftests, but all of
the pkey activity is performed in the parent.  The child does not perform
any actions sensitive to pkey state.

To make the test more sensitive to these kinds of bugs, add a fork() where
the parent exits, and execution continues in the child.

To achieve this let the key exhaustion test not terminate at the first
allocation failure and fork after 2*NR_PKEYS loops and continue in the
child.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: bp@alien8.de
Cc: hpa@zytor.com
Cc: peterz@infradead.org
Cc: mpe@ellerman.id.au
Cc: will.deacon@arm.com
Cc: luto@kernel.org
Cc: jroedel@suse.de
Cc: stable@vger.kernel.org
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Joerg Roedel <jroedel@suse.de>
Link: https://lkml.kernel.org/r/20190102215657.585704B7@viggo.jf.intel.com

tools/testing/selftests/x86/protection_keys.c

@@ -1133,6 +1133,21 @@ void test_pkey_syscalls_bad_args(int *ptr, u16 pkey)
 	pkey_assert(err);
 }
 
+void become_child(void)
+{
+	pid_t forkret;
+
+	forkret = fork();
+	pkey_assert(forkret >= 0);
+	dprintf3("[%d] fork() ret: %d\n", getpid(), forkret);
+
+	if (!forkret) {
+		/* in the child */
+		return;
+	}
+	exit(0);
+}
+
 /* Assumes that all pkeys other than 'pkey' are unallocated */
 void test_pkey_alloc_exhaust(int *ptr, u16 pkey)
 {
@@ -1141,7 +1156,7 @@ void test_pkey_alloc_exhaust(int *ptr, u16 pkey)
 	int nr_allocated_pkeys = 0;
 	int i;
 
-	for (i = 0; i < NR_PKEYS*2; i++) {
+	for (i = 0; i < NR_PKEYS*3; i++) {
 		int new_pkey;
 		dprintf1("%s() alloc loop: %d\n", __func__, i);
 		new_pkey = alloc_pkey();
@@ -1152,20 +1167,26 @@ void test_pkey_alloc_exhaust(int *ptr, u16 pkey)
 		if ((new_pkey == -1) && (errno == ENOSPC)) {
 			dprintf2("%s() failed to allocate pkey after %d tries\n",
 				__func__, nr_allocated_pkeys);
-			break;
+		} else {
+			/*
+			 * Ensure the number of successes never
+			 * exceeds the number of keys supported
+			 * in the hardware.
+			 */
+			pkey_assert(nr_allocated_pkeys < NR_PKEYS);
+			allocated_pkeys[nr_allocated_pkeys++] = new_pkey;
 		}
-		pkey_assert(nr_allocated_pkeys < NR_PKEYS);
-		allocated_pkeys[nr_allocated_pkeys++] = new_pkey;
+
+		/*
+		 * Make sure that allocation state is properly
+		 * preserved across fork().
+		 */
+		if (i == NR_PKEYS*2)
+			become_child();
 	}
 
 	dprintf3("%s()::%d\n", __func__, __LINE__);
 
-	/*
-	 * ensure it did not reach the end of the loop without
-	 * failure:
-	 */
-	pkey_assert(i < NR_PKEYS*2);
-
 	/*
 	 * There are 16 pkeys supported in hardware.  Three are
 	 * allocated by the time we get here: