lkdtm: Add -fstack-protector-strong test

There wasn't an LKDTM test to distinguish between -fstack-protector and
-fstack-protector-strong in use. This adds CORRUPT_STACK_STRONG to see
the difference. Also adjusts the stack-clobber value to 0xff so execution
won't potentially jump into userspace when the stack protector is missing.

Signed-off-by: Kees Cook <keescook@chromium.org>

diff --git a/drivers/misc/lkdtm.h b/drivers/misc/lkdtm.h
index 3c8627c..bfb6c45 100644 (file)
--- a/drivers/misc/lkdtm.h
+++ b/drivers/misc/lkdtm.h
@@ -14,6 +14,7 @@ void lkdtm_EXCEPTION(void);
 void lkdtm_LOOP(void);
 void lkdtm_OVERFLOW(void);
 void lkdtm_CORRUPT_STACK(void);
+void lkdtm_CORRUPT_STACK_STRONG(void);
 void lkdtm_UNALIGNED_LOAD_STORE_WRITE(void);
 void lkdtm_SOFTLOCKUP(void);
 void lkdtm_HARDLOCKUP(void);

diff --git a/drivers/misc/lkdtm_bugs.c b/drivers/misc/lkdtm_bugs.c
index 041fe6e..9e0b4f9 100644 (file)
--- a/drivers/misc/lkdtm_bugs.c
+++ b/drivers/misc/lkdtm_bugs.c
@@ -85,16 +85,31 @@ void lkdtm_OVERFLOW(void)
 
 static noinline void __lkdtm_CORRUPT_STACK(void *stack)
 {
-       memset(stack, 'a', 64);
+       memset(stack, '\xff', 64);
 }
 
+/* This should trip the stack canary, not corrupt the return address. */
 noinline void lkdtm_CORRUPT_STACK(void)
 {
        /* Use default char array length that triggers stack protection. */
-       char data[8];
+       char data[8] __aligned(sizeof(void *));
+
+       __lkdtm_CORRUPT_STACK(&data);
+
+       pr_info("Corrupted stack containing char array ...\n");
+}
+
+/* Same as above but will only get a canary with -fstack-protector-strong */
+noinline void lkdtm_CORRUPT_STACK_STRONG(void)
+{
+       union {
+               unsigned short shorts[4];
+               unsigned long *ptr;
+       } data __aligned(sizeof(void *));
+
        __lkdtm_CORRUPT_STACK(&data);
 
-       pr_info("Corrupted stack with '%16s'...\n", data);
+       pr_info("Corrupted stack containing union ...\n");
 }
 
 void lkdtm_UNALIGNED_LOAD_STORE_WRITE(void)

diff --git a/drivers/misc/lkdtm_core.c b/drivers/misc/lkdtm_core.c
index 9e98d7e..981b3ef 100644 (file)
--- a/drivers/misc/lkdtm_core.c
+++ b/drivers/misc/lkdtm_core.c
@@ -201,6 +201,7 @@ struct crashtype crashtypes[] = {
        CRASHTYPE(CORRUPT_LIST_DEL),
        CRASHTYPE(CORRUPT_USER_DS),
        CRASHTYPE(CORRUPT_STACK),
+       CRASHTYPE(CORRUPT_STACK_STRONG),
        CRASHTYPE(STACK_GUARD_PAGE_LEADING),
        CRASHTYPE(STACK_GUARD_PAGE_TRAILING),
        CRASHTYPE(UNALIGNED_LOAD_STORE_WRITE),