From 7b25a85c9d9f796c5be7ad3fb8b9553d3e2ed958 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Fri, 4 Aug 2017 13:04:21 -0700 Subject: [PATCH 1/2] lkdtm: Test VMAP_STACK allocates leading/trailing guard pages Two new tests STACK_GUARD_PAGE_LEADING and STACK_GUARD_PAGE_TRAILING attempt to read the byte before and after, respectively, of the current stack frame, which should fault. Signed-off-by: Kees Cook --- drivers/misc/lkdtm.h | 2 ++ drivers/misc/lkdtm_bugs.c | 30 ++++++++++++++++++++++++++++++ drivers/misc/lkdtm_core.c | 2 ++ 3 files changed, 34 insertions(+) diff --git a/drivers/misc/lkdtm.h b/drivers/misc/lkdtm.h index 063f5d651076..3c8627ca5f42 100644 --- a/drivers/misc/lkdtm.h +++ b/drivers/misc/lkdtm.h @@ -22,6 +22,8 @@ void lkdtm_HUNG_TASK(void); void lkdtm_CORRUPT_LIST_ADD(void); void lkdtm_CORRUPT_LIST_DEL(void); void lkdtm_CORRUPT_USER_DS(void); +void lkdtm_STACK_GUARD_PAGE_LEADING(void); +void lkdtm_STACK_GUARD_PAGE_TRAILING(void); /* lkdtm_heap.c */ void lkdtm_OVERWRITE_ALLOCATION(void); diff --git a/drivers/misc/lkdtm_bugs.c b/drivers/misc/lkdtm_bugs.c index ef3d06f901fc..041fe6e9532a 100644 --- a/drivers/misc/lkdtm_bugs.c +++ b/drivers/misc/lkdtm_bugs.c @@ -8,6 +8,7 @@ #include #include #include +#include #include struct lkdtm_list { @@ -199,6 +200,7 @@ void lkdtm_CORRUPT_LIST_DEL(void) pr_err("list_del() corruption not detected!\n"); } +/* Test if unbalanced set_fs(KERNEL_DS)/set_fs(USER_DS) check exists. */ void lkdtm_CORRUPT_USER_DS(void) { pr_info("setting bad task size limit\n"); @@ -207,3 +209,31 @@ void lkdtm_CORRUPT_USER_DS(void) /* Make sure we do not keep running with a KERNEL_DS! */ force_sig(SIGKILL, current); } + +/* Test that VMAP_STACK is actually allocating with a leading guard page */ +void lkdtm_STACK_GUARD_PAGE_LEADING(void) +{ + const unsigned char *stack = task_stack_page(current); + const unsigned char *ptr = stack - 1; + volatile unsigned char byte; + + pr_info("attempting bad read from page below current stack\n"); + + byte = *ptr; + + pr_err("FAIL: accessed page before stack!\n"); +} + +/* Test that VMAP_STACK is actually allocating with a trailing guard page */ +void lkdtm_STACK_GUARD_PAGE_TRAILING(void) +{ + const unsigned char *stack = task_stack_page(current); + const unsigned char *ptr = stack + THREAD_SIZE; + volatile unsigned char byte; + + pr_info("attempting bad read from page above current stack\n"); + + byte = *ptr; + + pr_err("FAIL: accessed page after stack!\n"); +} diff --git a/drivers/misc/lkdtm_core.c b/drivers/misc/lkdtm_core.c index 51decc07eeda..9e98d7ef5503 100644 --- a/drivers/misc/lkdtm_core.c +++ b/drivers/misc/lkdtm_core.c @@ -201,6 +201,8 @@ struct crashtype crashtypes[] = { CRASHTYPE(CORRUPT_LIST_DEL), CRASHTYPE(CORRUPT_USER_DS), CRASHTYPE(CORRUPT_STACK), + CRASHTYPE(STACK_GUARD_PAGE_LEADING), + CRASHTYPE(STACK_GUARD_PAGE_TRAILING), CRASHTYPE(UNALIGNED_LOAD_STORE_WRITE), CRASHTYPE(OVERWRITE_ALLOCATION), CRASHTYPE(WRITE_AFTER_FREE), From 93e78c6b14c42abe4018c815aeea2aa491522fae Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Fri, 4 Aug 2017 14:34:40 -0700 Subject: [PATCH 2/2] 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 --- drivers/misc/lkdtm.h | 1 + drivers/misc/lkdtm_bugs.c | 21 ++++++++++++++++++--- drivers/misc/lkdtm_core.c | 1 + 3 files changed, 20 insertions(+), 3 deletions(-) diff --git a/drivers/misc/lkdtm.h b/drivers/misc/lkdtm.h index 3c8627ca5f42..bfb6c45b6130 100644 --- 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 041fe6e9532a..9e0b4f959987 100644 --- 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 with '%16s'...\n", 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 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 9e98d7ef5503..981b3ef71e47 100644 --- 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),