[PATCH 01/12] lkdtm: add usercopy test for blocking kernel text

[Kees Cook]

The upcoming HARDENED_USERCOPY checks will also block access to the
kernel text, so provide a test for this as well.

Signed-off-by: Kees Cook <keesc...@chromium.org>
---
 drivers/misc/lkdtm_core.c | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/drivers/misc/lkdtm_core.c b/drivers/misc/lkdtm_core.c
index a595a6f2615a..23d222a6c77d 100644
--- a/drivers/misc/lkdtm_core.c
+++ b/drivers/misc/lkdtm_core.c
@@ -47,6 +47,7 @@
 #include <linux/vmalloc.h>
 #include <linux/mman.h>
 #include <asm/cacheflush.h>
+#include <asm/sections.h>
 
 #ifdef CONFIG_IDE
 #include <linux/ide.h>
@@ -120,6 +121,7 @@ enum ctype {
        CT_USERCOPY_STACK_FRAME_TO,
        CT_USERCOPY_STACK_FRAME_FROM,
        CT_USERCOPY_STACK_BEYOND,
+       CT_USERCOPY_KERNEL,
 };
 
 static char* cp_name[] = {
@@ -171,6 +173,7 @@ static char* cp_type[] = {
        "USERCOPY_STACK_FRAME_TO",
        "USERCOPY_STACK_FRAME_FROM",
        "USERCOPY_STACK_BEYOND",
+       "USERCOPY_KERNEL",
 };
 
 static struct jprobe lkdtm;
@@ -495,6 +498,35 @@ free_user:
        vm_munmap(user_addr, PAGE_SIZE);
 }
 
+static void do_usercopy_kernel(void)
+{
+       unsigned long user_addr;
+
+       user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
+                           PROT_READ | PROT_WRITE | PROT_EXEC,
+                           MAP_ANONYMOUS | MAP_PRIVATE, 0);
+       if (user_addr >= TASK_SIZE) {
+               pr_warn("Failed to allocate user memory\n");
+               return;
+       }
+
+       pr_info("attempting good copy_to_user from kernel rodata\n");
+       if (copy_to_user((void __user *)user_addr, test_text,
+                        sizeof(test_text))) {
+               pr_warn("copy_to_user failed unexpectedly?!\n");
+               goto free_user;
+       }
+
+       pr_info("attempting bad copy_to_user from kernel text\n");
+       if (copy_to_user((void __user *)user_addr, _stext, PAGE_SIZE)) {
+               pr_warn("copy_to_user failed, but lacked Oops\n");
+               goto free_user;
+       }
+
+free_user:
+       vm_munmap(user_addr, PAGE_SIZE);
+}
+
 static void do_usercopy_heap_size(bool to_user)
 {
        unsigned long user_addr;
@@ -957,6 +989,9 @@ static void lkdtm_do_action(enum ctype which)
        case CT_USERCOPY_STACK_BEYOND:
                do_usercopy_stack(true, false);
                break;
+       case CT_USERCOPY_KERNEL:
+               do_usercopy_kernel();
+               break;
        case CT_NONE:
        default:
                break;
-- 
2.7.4