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lkdtm: Provide timing tests for atomic_t vs refcount_t 

While not a crash test, this does provide two tight atomic_t and
refcount_t loops for performance comparisons:

	cd /sys/kernel/debug/provoke-crash
	perf stat -B -- cat <(echo ATOMIC_TIMING) > DIRECT
	perf stat -B -- cat <(echo REFCOUNT_TIMING) > DIRECT

Looking a CPU cycles is the best way to example the fast-path (rather
than instruction counts, since conditional jumps will be executed but
will be negligible due to branch-prediction).

Signed-off-by: Kees Cook <keescook@chromium.org>
This commit is contained in:
Kees Cook 2017-07-21 06:19:14 -07:00
parent 95925c99b9
commit c7fea48876
3 changed files with 48 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
drivers/misc/lkdtm.h
View File

@ -61,6 +61,8 @@ void lkdtm_REFCOUNT_INC_NOT_ZERO_SATURATED(void);
void lkdtm_REFCOUNT_ADD_NOT_ZERO_SATURATED(void);
void lkdtm_REFCOUNT_DEC_AND_TEST_SATURATED(void);
void lkdtm_REFCOUNT_SUB_AND_TEST_SATURATED(void);
void lkdtm_REFCOUNT_TIMING(void);
void lkdtm_ATOMIC_TIMING(void);
/* lkdtm_rodata.c */
void lkdtm_rodata_do_nothing(void);

2
drivers/misc/lkdtm_core.c
View File

@ -238,6 +238,8 @@ struct crashtype crashtypes[] = {
CRASHTYPE(REFCOUNT_ADD_NOT_ZERO_SATURATED),
CRASHTYPE(REFCOUNT_DEC_AND_TEST_SATURATED),
CRASHTYPE(REFCOUNT_SUB_AND_TEST_SATURATED),
CRASHTYPE(REFCOUNT_TIMING),
CRASHTYPE(ATOMIC_TIMING),
CRASHTYPE(USERCOPY_HEAP_SIZE_TO),
CRASHTYPE(USERCOPY_HEAP_SIZE_FROM),
CRASHTYPE(USERCOPY_HEAP_FLAG_TO),

44
drivers/misc/lkdtm_refcount.c
View File

@ -354,3 +354,47 @@ void lkdtm_REFCOUNT_SUB_AND_TEST_SATURATED(void)
check_saturated(&sat);
}
/* Used to time the existing atomic_t when used for reference counting */
void lkdtm_ATOMIC_TIMING(void)
{
unsigned int i;
atomic_t count = ATOMIC_INIT(1);
for (i = 0; i < INT_MAX - 1; i++)
atomic_inc(&count);
for (i = INT_MAX; i > 0; i--)
if (atomic_dec_and_test(&count))
break;
if (i != 1)
pr_err("atomic timing: out of sync up/down cycle: %u\n", i - 1);
else
pr_info("atomic timing: done\n");
}
/*
* This can be compared to ATOMIC_TIMING when implementing fast refcount
* protections. Looking at the number of CPU cycles tells the real story
* about performance. For example:
* cd /sys/kernel/debug/provoke-crash
* perf stat -B -- cat <(echo REFCOUNT_TIMING) > DIRECT
*/
void lkdtm_REFCOUNT_TIMING(void)
{
unsigned int i;
refcount_t count = REFCOUNT_INIT(1);
for (i = 0; i < INT_MAX - 1; i++)
refcount_inc(&count);
for (i = INT_MAX; i > 0; i--)
if (refcount_dec_and_test(&count))
break;
if (i != 1)
pr_err("refcount: out of sync up/down cycle: %u\n", i - 1);
else
pr_info("refcount timing: done\n");
}