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authorKees Cook <keescook@chromium.org>2017-07-21 06:19:14 -0700
committerKees Cook <keescook@chromium.org>2017-07-26 14:38:04 -0700
commitc7fea48876773603721f545f8c1a2f894291ef85 (patch)
tree8aec6293f664c8240af323fd017682f64d3b5b64 /drivers/misc
parent95925c99b9043d52db626645e6ef5ee5f62c97e4 (diff)
downloadlinux-c7fea48876773603721f545f8c1a2f894291ef85.tar.bz2
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>
Diffstat (limited to 'drivers/misc')
-rw-r--r--drivers/misc/lkdtm.h2
-rw-r--r--drivers/misc/lkdtm_core.c2
-rw-r--r--drivers/misc/lkdtm_refcount.c44
3 files changed, 48 insertions, 0 deletions
diff --git a/drivers/misc/lkdtm.h b/drivers/misc/lkdtm.h
index 04ff8b23b3b0..063f5d651076 100644
--- a/drivers/misc/lkdtm.h
+++ b/drivers/misc/lkdtm.h
@@ -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);
diff --git a/drivers/misc/lkdtm_core.c b/drivers/misc/lkdtm_core.c
index 156a1a07c3db..51decc07eeda 100644
--- a/drivers/misc/lkdtm_core.c
+++ b/drivers/misc/lkdtm_core.c
@@ -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),
diff --git a/drivers/misc/lkdtm_refcount.c b/drivers/misc/lkdtm_refcount.c
index 313abea4bf9d..29af0152a337 100644
--- a/drivers/misc/lkdtm_refcount.c
+++ b/drivers/misc/lkdtm_refcount.c
@@ -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");
+}