usercopy: Adjust tests to deal with SMAP/PAN

Under SMAP/PAN/etc, we cannot write directly to userspace memory, so
this rearranges the test bytes to get written through copy_to_user().
Additionally drops the bad copy_from_user() test that would trigger a
memcpy() against userspace on failure.

Signed-off-by: Kees Cook <keescook@chromium.org>

diff --git a/lib/test_user_copy.c b/lib/test_user_copy.c
index 0f86c67d87dbba95921aa4de4ad02a2f16f45633..73ff7a628e3a14c88c4b861e78225891d45cd571 100644 (file)
--- a/lib/test_user_copy.c
+++ b/lib/test_user_copy.c
@@ -58,7 +58,9 @@ static int __init test_user_copy_init(void)
        usermem = (char __user *)user_addr;
        bad_usermem = (char *)user_addr;
 
-       /* Legitimate usage: none of these should fail. */
+       /*
+        * Legitimate usage: none of these copies should fail.
+        */
        ret |= test(copy_from_user(kmem, usermem, PAGE_SIZE),
                    "legitimate copy_from_user failed");
        ret |= test(copy_to_user(usermem, kmem, PAGE_SIZE),
@@ -68,31 +70,45 @@ static int __init test_user_copy_init(void)
        ret |= test(put_user(value, (unsigned long __user *)usermem),
                    "legitimate put_user failed");
 
-       /* Invalid usage: none of these should succeed. */
+       /*
+        * Invalid usage: none of these copies should succeed.
+        */
+
+       /* Prepare kernel memory with check values. */
        memset(kmem, 0x5a, PAGE_SIZE);
        memset(kmem + PAGE_SIZE, 0, PAGE_SIZE);
+
+       /* Reject kernel-to-kernel copies through copy_from_user(). */
        ret |= test(!copy_from_user(kmem, (char __user *)(kmem + PAGE_SIZE),
                                    PAGE_SIZE),
                    "illegal all-kernel copy_from_user passed");
+
+       /* Destination half of buffer should have been zeroed. */
        ret |= test(memcmp(kmem + PAGE_SIZE, kmem, PAGE_SIZE),
                    "zeroing failure for illegal all-kernel copy_from_user");
-       memset(bad_usermem, 0x5A, PAGE_SIZE);
+
+#if 0
+       /*
+        * When running with SMAP/PAN/etc, this will Oops the kernel
+        * due to the zeroing of userspace memory on failure. This needs
+        * to be tested in LKDTM instead, since this test module does not
+        * expect to explode.
+        */
        ret |= test(!copy_from_user(bad_usermem, (char __user *)kmem,
                                    PAGE_SIZE),
                    "illegal reversed copy_from_user passed");
-       ret |= test(memcmp(kmem + PAGE_SIZE, bad_usermem, PAGE_SIZE),
-                   "zeroing failure for illegal reversed copy_from_user");
+#endif
        ret |= test(!copy_to_user((char __user *)kmem, kmem + PAGE_SIZE,
                                  PAGE_SIZE),
                    "illegal all-kernel copy_to_user passed");
        ret |= test(!copy_to_user((char __user *)kmem, bad_usermem,
                                  PAGE_SIZE),
                    "illegal reversed copy_to_user passed");
-       memset(kmem, 0x5a, PAGE_SIZE);
+
+       value = 0x5a;
        ret |= test(!get_user(value, (unsigned long __user *)kmem),
                    "illegal get_user passed");
-       ret |= test(memcmp(kmem + PAGE_SIZE, kmem, sizeof(value)),
-                   "zeroing failure for illegal get_user");
+       ret |= test(value != 0, "zeroing failure for illegal get_user");
        ret |= test(!put_user(value, (unsigned long __user *)kmem),
                    "illegal put_user passed");