[PATCH] [v2] selftests, x86, pkeys: test with random, unallocated protection keys

[Dave Hansen]

Changes from v1:
 * Also generate random negative numbers for protection key

--
From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>

The kernel pkeys code had a minor bug where it did some large shifts
to an integer which is undefined behavior in C.  It didn't cause any
real harm, but it is screwy behavior that the kernel should have
rejected.

Add a test case for this.

Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Cc: linux-kselftest@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: x86@xxxxxxxxxx
---

 b/tools/testing/selftests/x86/protection_keys.c |   25 ++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff -puN tools/testing/selftests/x86/protection_keys.c~pkeys-better-selftests-of-random-pkey tools/testing/selftests/x86/protection_keys.c
--- a/tools/testing/selftests/x86/protection_keys.c~pkeys-better-selftests-of-random-pkey	2017-02-23 14:24:34.323744591 -0800
+++ b/tools/testing/selftests/x86/protection_keys.c	2017-02-23 16:14:06.101005910 -0800
@@ -1123,6 +1123,30 @@ void test_pkey_syscalls_on_non_allocated
 }
 
 /* Assumes that all pkeys other than 'pkey' are unallocated */
+void test_pkey_syscalls_on_non_allocated_random_pkey(int *ptr, u16 pkey)
+{
+	int err;
+	int nr_tests = 0;
+
+	while (nr_tests < 1000) {
+		int test_pkey = rand() - RAND_MAX/2;
+
+		/* do not test with the pkey we know is good */
+		if (pkey == test_pkey)
+			continue;
+
+		dprintf1("trying free/mprotect bad pkey: %2d\n", test_pkey);
+		err = sys_pkey_free(test_pkey);
+		pkey_assert(err);
+
+		err = sys_mprotect_pkey(ptr, PAGE_SIZE, PROT_READ, test_pkey);
+		pkey_assert(err);
+
+		nr_tests++;
+	}
+}
+
+/* Assumes that all pkeys other than 'pkey' are unallocated */
 void test_pkey_syscalls_bad_args(int *ptr, u16 pkey)
 {
 	int err;
@@ -1320,6 +1344,7 @@ void (*pkey_tests[])(int *ptr, u16 pkey)
 	test_executing_on_unreadable_memory,
 	test_ptrace_of_child,
 	test_pkey_syscalls_on_non_allocated_pkey,
+	test_pkey_syscalls_on_non_allocated_random_pkey,
 	test_pkey_syscalls_bad_args,
 	test_pkey_alloc_exhaust,
 };
_