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>

1 files changed, 24 insertions, 8 deletions

diff --git a/lib/test_user_copy.c b/lib/test_user_copy.c
index 0f86c67d87db..73ff7a628e3a 100644
--- 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");