From: Sami Tolvanen <samitolvanen@google.com>
Date: Thu, 8 Apr 2021 18:28:35 +0000 (-0700)
Subject: lkdtm: use function_nocfi
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=6c4df54ed293f6383efb97fca0e643b8dcbc3769;p=linux.git

lkdtm: use function_nocfi

To ensure we take the actual address of a function in kernel text,
use function_nocfi. Otherwise, with CONFIG_CFI_CLANG, the compiler
replaces the address with a pointer to the CFI jump table, which is
actually in the module when compiled with CONFIG_LKDTM=m.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Acked-by: Kees Cook <keescook@chromium.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210408182843.1754385-11-samitolvanen@google.com
---

diff --git a/drivers/misc/lkdtm/usercopy.c b/drivers/misc/lkdtm/usercopy.c
index 109e8d4302c11..15d220ef35a56 100644
--- a/drivers/misc/lkdtm/usercopy.c
+++ b/drivers/misc/lkdtm/usercopy.c
@@ -314,7 +314,7 @@ void lkdtm_USERCOPY_KERNEL(void)
 
 	pr_info("attempting bad copy_to_user from kernel text: %px\n",
 		vm_mmap);
-	if (copy_to_user((void __user *)user_addr, vm_mmap,
+	if (copy_to_user((void __user *)user_addr, function_nocfi(vm_mmap),
 			 unconst + PAGE_SIZE)) {
 		pr_warn("copy_to_user failed, but lacked Oops\n");
 		goto free_user;