test: check copy_to/from_user boundary validation

To help avoid an architecture failing to correctly check kernel/user
boundaries when handling copy_to_user, copy_from_user, put_user, or
get_user, perform some simple tests and fail to load if any of them
behave unexpectedly.

Specifically, this is to make sure there is a way to notice if things
like what was fixed in commit 8404663f81d2 ("ARM: 7527/1: uaccess:
explicitly check __user pointer when !CPU_USE_DOMAINS") ever regresses
again, for any architecture.

Additionally, adds new "user" selftest target, which loads this module.

Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 13 insertions, 0 deletions

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 7e37a36b6913..e0e2eebf7ab3 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1609,6 +1609,19 @@ config TEST_MODULE
 
           If unsure, say N.
 
+config TEST_USER_COPY
+        tristate "Test user/kernel boundary protections"
+        default n
+        depends on m
+        help
+          This builds the "test_user_copy" module that runs sanity checks
+          on the copy_to/from_user infrastructure, making sure basic
+          user/kernel boundary testing is working. If it fails to load,
+          a regression has been detected in the user/kernel memory boundary
+          protections.
+
+          If unsure, say N.
+
 source "samples/Kconfig"
 
 source "lib/Kconfig.kgdb"