[tip:x86/core] lkdtm: Test copy_to_user() on bad kernel pointer under KERNEL_DS

[tip-bot for Jann Horn]

Commit-ID:  bef459026b161fbc39d20dcba698ed0cfffbac38
Gitweb:     https://git.kernel.org/tip/bef459026b161fbc39d20dcba698ed0cfffbac38
Author:     Jann Horn <jannh@xxxxxxxxxx>
AuthorDate: Tue, 28 Aug 2018 22:14:21 +0200
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Mon, 3 Sep 2018 15:12:10 +0200

lkdtm: Test copy_to_user() on bad kernel pointer under KERNEL_DS

Test whether the kernel WARN()s when, under KERNEL_DS, a bad kernel pointer
is used as "userspace" pointer. Should normally be used in "DIRECT" mode.

Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Tested-by: Kees Cook <keescook@xxxxxxxxxxxx>
Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: kernel-hardening@xxxxxxxxxxxxxxxxxx
Cc: dvyukov@xxxxxxxxxx
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: "Naveen N. Rao" <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@xxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: linux-fsdevel@xxxxxxxxxxxxxxx
Cc: Borislav Petkov <bp@xxxxxxxxx>
Link: https://lkml.kernel.org/r/20180828201421.157735-8-jannh@xxxxxxxxxx

---
 drivers/misc/lkdtm/core.c     |  1 +
 drivers/misc/lkdtm/lkdtm.h    |  1 +
 drivers/misc/lkdtm/usercopy.c | 13 +++++++++++++
 3 files changed, 15 insertions(+)

diff --git a/drivers/misc/lkdtm/core.c b/drivers/misc/lkdtm/core.c
index 2154d1bfd18b..5a755590d3dc 100644
--- a/drivers/misc/lkdtm/core.c
+++ b/drivers/misc/lkdtm/core.c
@@ -183,6 +183,7 @@ static const struct crashtype crashtypes[] = {
 	CRASHTYPE(USERCOPY_STACK_FRAME_FROM),
 	CRASHTYPE(USERCOPY_STACK_BEYOND),
 	CRASHTYPE(USERCOPY_KERNEL),
+	CRASHTYPE(USERCOPY_KERNEL_DS),
 };
 
 
diff --git a/drivers/misc/lkdtm/lkdtm.h b/drivers/misc/lkdtm/lkdtm.h
index 9e513dcfd809..07db641d71d0 100644
--- a/drivers/misc/lkdtm/lkdtm.h
+++ b/drivers/misc/lkdtm/lkdtm.h
@@ -82,5 +82,6 @@ void lkdtm_USERCOPY_STACK_FRAME_TO(void);
 void lkdtm_USERCOPY_STACK_FRAME_FROM(void);
 void lkdtm_USERCOPY_STACK_BEYOND(void);
 void lkdtm_USERCOPY_KERNEL(void);
+void lkdtm_USERCOPY_KERNEL_DS(void);
 
 #endif
diff --git a/drivers/misc/lkdtm/usercopy.c b/drivers/misc/lkdtm/usercopy.c
index 9725aed305bb..389475b25bb7 100644
--- a/drivers/misc/lkdtm/usercopy.c
+++ b/drivers/misc/lkdtm/usercopy.c
@@ -322,6 +322,19 @@ free_user:
 	vm_munmap(user_addr, PAGE_SIZE);
 }
 
+void lkdtm_USERCOPY_KERNEL_DS(void)
+{
+	char __user *user_ptr = (char __user *)ERR_PTR(-EINVAL);
+	mm_segment_t old_fs = get_fs();
+	char buf[10] = {0};
+
+	pr_info("attempting copy_to_user on unmapped kernel address\n");
+	set_fs(KERNEL_DS);
+	if (copy_to_user(user_ptr, buf, sizeof(buf)))
+		pr_info("copy_to_user un unmapped kernel address failed\n");
+	set_fs(old_fs);
+}
+
 void __init lkdtm_usercopy_init(void)
 {
 	/* Prepare cache that lacks SLAB_USERCOPY flag. */