[PATCH 4.9 31/44] x86/selftests/pkeys: Fork() to check for state being preserved

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>

commit e1812933b17be7814f51b6c310c5d1ced7a9a5f5 upstream.

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@xxxxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: bp@xxxxxxxxx
Cc: hpa@xxxxxxxxx
Cc: peterz@xxxxxxxxxxxxx
Cc: mpe@xxxxxxxxxxxxxx
Cc: will.deacon@xxxxxxx
Cc: luto@xxxxxxxxxx
Cc: jroedel@xxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Joerg Roedel <jroedel@xxxxxxx>
Link: https://lkml.kernel.org/r/20190102215657.585704B7@xxxxxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 tools/testing/selftests/x86/protection_keys.c |   41 +++++++++++++++++++-------
 1 file changed, 31 insertions(+), 10 deletions(-)

--- a/tools/testing/selftests/x86/protection_keys.c
+++ b/tools/testing/selftests/x86/protection_keys.c
@@ -1129,6 +1129,21 @@ void test_pkey_syscalls_bad_args(int *pt
 	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)
 {
@@ -1139,7 +1154,7 @@ void test_pkey_alloc_exhaust(int *ptr, u
 	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();
@@ -1150,21 +1165,27 @@ void test_pkey_alloc_exhaust(int *ptr, u
 		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.  One is taken
 	 * up for the default (0) and another can be taken up by
 	 * an execute-only mapping.  Ensure that we can allocate