[PATCH AUTOSEL 4.9 17/21] lkdtm: Add tests for NULL pointer dereference

[Sasha Levin <sashal@kernel.org>]

From: Christophe Leroy <christophe.leroy@c-s.fr>

[ Upstream commit 59a12205d3c32aee4c13ca36889fdf7cfed31126 ]

Introduce lkdtm tests for NULL pointer dereference: check access or exec
at NULL address, since these errors tend to be reported differently from
the general fault error text. For example from x86:

    pr_alert("BUG: unable to handle kernel %s at %px\n",
        address < PAGE_SIZE ? "NULL pointer dereference" : "paging request",
        (void *)address);

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/misc/lkdtm.h       |  2 ++
 drivers/misc/lkdtm_core.c  |  2 ++
 drivers/misc/lkdtm_perms.c | 18 ++++++++++++++++++
 3 files changed, 22 insertions(+)

diff --git a/drivers/misc/lkdtm.h b/drivers/misc/lkdtm.h
index fdf954c2107f..6abc97b245e4 100644
--- a/drivers/misc/lkdtm.h
+++ b/drivers/misc/lkdtm.h
@@ -40,7 +40,9 @@ void lkdtm_EXEC_KMALLOC(void);
 void lkdtm_EXEC_VMALLOC(void);
 void lkdtm_EXEC_RODATA(void);
 void lkdtm_EXEC_USERSPACE(void);
+void lkdtm_EXEC_NULL(void);
 void lkdtm_ACCESS_USERSPACE(void);
+void lkdtm_ACCESS_NULL(void);
 
 /* lkdtm_rodata.c */
 void lkdtm_rodata_do_nothing(void);
diff --git a/drivers/misc/lkdtm_core.c b/drivers/misc/lkdtm_core.c
index b2989f2d3126..035e51bea450 100644
--- a/drivers/misc/lkdtm_core.c
+++ b/drivers/misc/lkdtm_core.c
@@ -214,7 +214,9 @@ struct crashtype crashtypes[] = {
 	CRASHTYPE(EXEC_VMALLOC),
 	CRASHTYPE(EXEC_RODATA),
 	CRASHTYPE(EXEC_USERSPACE),
+	CRASHTYPE(EXEC_NULL),
 	CRASHTYPE(ACCESS_USERSPACE),
+	CRASHTYPE(ACCESS_NULL),
 	CRASHTYPE(WRITE_RO),
 	CRASHTYPE(WRITE_RO_AFTER_INIT),
 	CRASHTYPE(WRITE_KERN),
diff --git a/drivers/misc/lkdtm_perms.c b/drivers/misc/lkdtm_perms.c
index 45f1c0f96612..1a9dcdaa95f0 100644
--- a/drivers/misc/lkdtm_perms.c
+++ b/drivers/misc/lkdtm_perms.c
@@ -160,6 +160,11 @@ void lkdtm_EXEC_USERSPACE(void)
 	vm_munmap(user_addr, PAGE_SIZE);
 }
 
+void lkdtm_EXEC_NULL(void)
+{
+	execute_location(NULL, CODE_AS_IS);
+}
+
 void lkdtm_ACCESS_USERSPACE(void)
 {
 	unsigned long user_addr, tmp = 0;
@@ -191,6 +196,19 @@ void lkdtm_ACCESS_USERSPACE(void)
 	vm_munmap(user_addr, PAGE_SIZE);
 }
 
+void lkdtm_ACCESS_NULL(void)
+{
+	unsigned long tmp;
+	unsigned long *ptr = (unsigned long *)NULL;
+
+	pr_info("attempting bad read at %px\n", ptr);
+	tmp = *ptr;
+	tmp += 0xc0dec0de;
+
+	pr_info("attempting bad write at %px\n", ptr);
+	*ptr = tmp;
+}
+
 void __init lkdtm_perms_init(void)
 {
 	/* Make sure we can write to __ro_after_init values during __init */
-- 
2.19.1