From 2bf8496f6e9b7e9a557f65eb95eab16fea7958c7 Mon Sep 17 00:00:00 2001
From: Kees Cook <keescook@chromium.org>
Date: Sat, 6 Apr 2019 08:52:11 -0700
Subject: [PATCH] lkdtm/usercopy: Moves the KERNEL_DS test to non-canonical
The prior implementation of the KERNEL_DS fault checking would work on
any unmapped kernel address, but this was narrowed to the non-canonical
range instead. This adjusts the LKDTM test to match.
Fixes: 00c42373d397 ("x86-64: add warning for non-canonical user access address dereferences")
Signed-off-by: Kees Cook <keescook@chromium.org>
---
drivers/misc/lkdtm/usercopy.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/drivers/misc/lkdtm/usercopy.c b/drivers/misc/lkdtm/usercopy.c
index d5a0e7f1813b1..e172719dd86d0 100644
--- a/drivers/misc/lkdtm/usercopy.c
+++ b/drivers/misc/lkdtm/usercopy.c
@@ -324,14 +324,16 @@ void lkdtm_USERCOPY_KERNEL(void)
void lkdtm_USERCOPY_KERNEL_DS(void)
{
- char __user *user_ptr = (char __user *)ERR_PTR(-EINVAL);
+ char __user *user_ptr =
+ (char __user *)(0xFUL << (sizeof(unsigned long) * 8 - 4));
mm_segment_t old_fs = get_fs();
char buf[10] = {0};
- pr_info("attempting copy_to_user on unmapped kernel address\n");
+ pr_info("attempting copy_to_user() to noncanonical address: %px\n",
+ user_ptr);
set_fs(KERNEL_DS);
- if (copy_to_user(user_ptr, buf, sizeof(buf)))
- pr_info("copy_to_user un unmapped kernel address failed\n");
+ if (copy_to_user(user_ptr, buf, sizeof(buf)) == 0)
+ pr_err("copy_to_user() to noncanonical address succeeded!?\n");
set_fs(old_fs);
}