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lkdtm/bugs: Adjust recursion test to avoid elision

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While I was able to trick gcc into keeping a pathological recursion,
Clang was not so easily fooled. Instead, switch to using "volatile" and
side-effects to keep the stack variable allocated and to run the function.
Additionally renames "OVERFLOW" to "EXHAUST_STACK" to better describe the
test.

Signed-off-by: Kees Cook <keescook@chromium.org>
This commit is contained in:
Kees Cook
2019-04-06 08:59:19 -07:00
parent 2bf8496f6e
commit 24cccab42c
3 changed files with 21 additions and 10 deletions
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23
drivers/misc/lkdtm/bugs.c
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@@ -32,12 +32,20 @@ static int recur_count = REC_NUM_DEFAULT;
static DEFINE_SPINLOCK(lock_me_up);
static int recursive_loop(int remaining)
/*
* Make sure compiler does not optimize this function or stack frame away:
* - function marked noinline
* - stack variables are marked volatile
* - stack variables are written (memset()) and read (pr_info())
* - function has external effects (pr_info())
* */
static int noinline recursive_loop(int remaining)
{
char buf[REC_STACK_SIZE];
volatile char buf[REC_STACK_SIZE];
/* Make sure compiler does not optimize this away. */
memset(buf, (remaining & 0xff) | 0x1, REC_STACK_SIZE);
memset((void *)buf, remaining & 0xFF, sizeof(buf));
pr_info("loop %d/%d ...\n", (int)buf[remaining % sizeof(buf)],
recur_count);
if (!remaining)
return 0;
else
@@ -81,9 +89,12 @@ void lkdtm_LOOP(void)
;
}
void lkdtm_OVERFLOW(void)
void lkdtm_EXHAUST_STACK(void)
{
(void) recursive_loop(recur_count);
pr_info("Calling function with %d frame size to depth %d ...\n",
REC_STACK_SIZE, recur_count);
recursive_loop(recur_count);
pr_info("FAIL: survived without exhausting stack?!\n");
}
static noinline void __lkdtm_CORRUPT_STACK(void *stack)