Messages in this thread Patch in this message | | | From | Kees Cook <> | Subject | [PATCH 2/2] lkdtm: Provide timing tests for atomic_t vs refcount_t | Date | Tue, 25 Jul 2017 11:33:57 -0700 |
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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> --- drivers/misc/lkdtm.h | 2 ++ drivers/misc/lkdtm_core.c | 2 ++ drivers/misc/lkdtm_refcount.c | 44 +++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 48 insertions(+)
diff --git a/drivers/misc/lkdtm.h b/drivers/misc/lkdtm.h index 241d6f3a26dd..0b86947b31f5 100644 --- a/drivers/misc/lkdtm.h +++ b/drivers/misc/lkdtm.h @@ -57,6 +57,8 @@ void lkdtm_REFCOUNT_DEC_SATURATED(void); void lkdtm_REFCOUNT_ADD_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); diff --git a/drivers/misc/lkdtm_core.c b/drivers/misc/lkdtm_core.c index c3b045aec10e..5f949a05b307 100644 --- a/drivers/misc/lkdtm_core.c +++ b/drivers/misc/lkdtm_core.c @@ -234,6 +234,8 @@ struct crashtype crashtypes[] = { CRASHTYPE(REFCOUNT_ADD_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), diff --git a/drivers/misc/lkdtm_refcount.c b/drivers/misc/lkdtm_refcount.c index 234d39a07a99..8bad7baf0119 100644 --- a/drivers/misc/lkdtm_refcount.c +++ b/drivers/misc/lkdtm_refcount.c @@ -306,3 +306,47 @@ 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; i++) + atomic_inc(&count); + + for (i = INT_MAX; i >= 0; i--) + if (atomic_dec_and_test(&count)) + break; + + if (i != 0) + pr_err("atomic timing: out of sync up/down cycle: %u\n", i); + 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; i++) + refcount_inc(&count); + + for (i = INT_MAX; i >= 0; i--) + if (refcount_dec_and_test(&count)) + break; + + if (i != 0) + pr_err("refcount: out of sync up/down cycle: %u\n", i); + else + pr_info("refcount timing: done\n"); +} -- 2.7.4
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