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locking/refcount: Define constants for saturation and max refcount values 

The REFCOUNT_FULL implementation uses a different saturation point than
the x86 implementation, which means that the shared refcount code in
lib/refcount.c (e.g. refcount_dec_not_one()) needs to be aware of the
difference.

Rather than duplicate the definitions from the lkdtm driver, instead
move them into <linux/refcount.h> and update all references accordingly.

Signed-off-by: Will Deacon <will@kernel.org>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Tested-by: Hanjun Guo <guohanjun@huawei.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Elena Reshetova <elena.reshetova@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20191121115902.2551-2-will@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Will Deacon 2019-11-21 11:58:53 +00:00 committed by Ingo Molnar
parent 3ef240eaff
commit 23e6b169c9
3 changed files with 29 additions and 26 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
drivers/misc/lkdtm/refcount.c
View File

@ -6,14 +6,6 @@
#include "lkdtm.h"
#include <linux/refcount.h>
#ifdef CONFIG_REFCOUNT_FULL
#define REFCOUNT_MAX (UINT_MAX - 1)
#define REFCOUNT_SATURATED UINT_MAX
#else
#define REFCOUNT_MAX INT_MAX
#define REFCOUNT_SATURATED (INT_MIN / 2)
#endif
static void overflow_check(refcount_t *ref)
{
switch (refcount_read(ref)) {

10
include/linux/refcount.h
View File

@ -4,6 +4,7 @@
#include <linux/atomic.h>
#include <linux/compiler.h>
#include <linux/limits.h>
#include <linux/spinlock_types.h>
struct mutex;
@ -12,7 +13,7 @@ struct mutex;
* struct refcount_t - variant of atomic_t specialized for reference counts
* @refs: atomic_t counter field
*
* The counter saturates at UINT_MAX and will not move once
* The counter saturates at REFCOUNT_SATURATED and will not move once
* there. This avoids wrapping the counter and causing 'spurious'
* use-after-free bugs.
*/
@ -56,6 +57,9 @@ extern void refcount_dec_checked(refcount_t *r);
#ifdef CONFIG_REFCOUNT_FULL
#define REFCOUNT_MAX (UINT_MAX - 1)
#define REFCOUNT_SATURATED UINT_MAX
#define refcount_add_not_zero refcount_add_not_zero_checked
#define refcount_add refcount_add_checked
@ -68,6 +72,10 @@ extern void refcount_dec_checked(refcount_t *r);
#define refcount_dec refcount_dec_checked
#else
#define REFCOUNT_MAX INT_MAX
#define REFCOUNT_SATURATED (INT_MIN / 2)
# ifdef CONFIG_ARCH_HAS_REFCOUNT
# include <asm/refcount.h>
# else

37
lib/refcount.c
View File

@ -5,8 +5,8 @@
* The interface matches the atomic_t interface (to aid in porting) but only
* provides the few functions one should use for reference counting.
*
* It differs in that the counter saturates at UINT_MAX and will not move once
* there. This avoids wrapping the counter and causing 'spurious'
* It differs in that the counter saturates at REFCOUNT_SATURATED and will not
* move once there. This avoids wrapping the counter and causing 'spurious'
* use-after-free issues.
*
* Memory ordering rules are slightly relaxed wrt regular atomic_t functions
@ -48,7 +48,7 @@
* @i: the value to add to the refcount
* @r: the refcount
*
* Will saturate at UINT_MAX and WARN.
* Will saturate at REFCOUNT_SATURATED and WARN.
*
* Provides no memory ordering, it is assumed the caller has guaranteed the
* object memory to be stable (RCU, etc.). It does provide a control dependency
@ -69,16 +69,17 @@ bool refcount_add_not_zero_checked(unsigned int i, refcount_t *r)
if (!val)
return false;
if (unlikely(val == UINT_MAX))
if (unlikely(val == REFCOUNT_SATURATED))
return true;
new = val + i;
if (new < val)
new = UINT_MAX;
new = REFCOUNT_SATURATED;
} while (!atomic_try_cmpxchg_relaxed(&r->refs, &val, new));
WARN_ONCE(new == UINT_MAX, "refcount_t: saturated; leaking memory.\n");
WARN_ONCE(new == REFCOUNT_SATURATED,
"refcount_t: saturated; leaking memory.\n");
return true;
}
@ -89,7 +90,7 @@ EXPORT_SYMBOL(refcount_add_not_zero_checked);
* @i: the value to add to the refcount
* @r: the refcount
*
* Similar to atomic_add(), but will saturate at UINT_MAX and WARN.
* Similar to atomic_add(), but will saturate at REFCOUNT_SATURATED and WARN.
*
* Provides no memory ordering, it is assumed the caller has guaranteed the
* object memory to be stable (RCU, etc.). It does provide a control dependency
@ -110,7 +111,8 @@ EXPORT_SYMBOL(refcount_add_checked);
* refcount_inc_not_zero_checked - increment a refcount unless it is 0
* @r: the refcount to increment
*
* Similar to atomic_inc_not_zero(), but will saturate at UINT_MAX and WARN.
* Similar to atomic_inc_not_zero(), but will saturate at REFCOUNT_SATURATED
* and WARN.
*
* Provides no memory ordering, it is assumed the caller has guaranteed the
* object memory to be stable (RCU, etc.). It does provide a control dependency
@ -133,7 +135,8 @@ bool refcount_inc_not_zero_checked(refcount_t *r)
} while (!atomic_try_cmpxchg_relaxed(&r->refs, &val, new));
WARN_ONCE(new == UINT_MAX, "refcount_t: saturated; leaking memory.\n");
WARN_ONCE(new == REFCOUNT_SATURATED,
"refcount_t: saturated; leaking memory.\n");
return true;
}
@ -143,7 +146,7 @@ EXPORT_SYMBOL(refcount_inc_not_zero_checked);
* refcount_inc_checked - increment a refcount
* @r: the refcount to increment
*
* Similar to atomic_inc(), but will saturate at UINT_MAX and WARN.
* Similar to atomic_inc(), but will saturate at REFCOUNT_SATURATED and WARN.
*
* Provides no memory ordering, it is assumed the caller already has a
* reference on the object.
@ -164,7 +167,7 @@ EXPORT_SYMBOL(refcount_inc_checked);
*
* Similar to atomic_dec_and_test(), but it will WARN, return false and
* ultimately leak on underflow and will fail to decrement when saturated
* at UINT_MAX.
* at REFCOUNT_SATURATED.
*
* Provides release memory ordering, such that prior loads and stores are done
* before, and provides an acquire ordering on success such that free()
@ -182,7 +185,7 @@ bool refcount_sub_and_test_checked(unsigned int i, refcount_t *r)
unsigned int new, val = atomic_read(&r->refs);
do {
if (unlikely(val == UINT_MAX))
if (unlikely(val == REFCOUNT_SATURATED))
return false;
new = val - i;
@ -207,7 +210,7 @@ EXPORT_SYMBOL(refcount_sub_and_test_checked);
* @r: the refcount
*
* Similar to atomic_dec_and_test(), it will WARN on underflow and fail to
* decrement when saturated at UINT_MAX.
* decrement when saturated at REFCOUNT_SATURATED.
*
* Provides release memory ordering, such that prior loads and stores are done
* before, and provides an acquire ordering on success such that free()
@ -226,7 +229,7 @@ EXPORT_SYMBOL(refcount_dec_and_test_checked);
* @r: the refcount
*
* Similar to atomic_dec(), it will WARN on underflow and fail to decrement
* when saturated at UINT_MAX.
* when saturated at REFCOUNT_SATURATED.
*
* Provides release memory ordering, such that prior loads and stores are done
* before.
@ -277,7 +280,7 @@ bool refcount_dec_not_one(refcount_t *r)
unsigned int new, val = atomic_read(&r->refs);
do {
if (unlikely(val == UINT_MAX))
if (unlikely(val == REFCOUNT_SATURATED))
return true;
if (val == 1)
@ -302,7 +305,7 @@ EXPORT_SYMBOL(refcount_dec_not_one);
* @lock: the mutex to be locked
*
* Similar to atomic_dec_and_mutex_lock(), it will WARN on underflow and fail
* to decrement when saturated at UINT_MAX.
* to decrement when saturated at REFCOUNT_SATURATED.
*
* Provides release memory ordering, such that prior loads and stores are done
* before, and provides a control dependency such that free() must come after.
@ -333,7 +336,7 @@ EXPORT_SYMBOL(refcount_dec_and_mutex_lock);
* @lock: the spinlock to be locked
*
* Similar to atomic_dec_and_lock(), it will WARN on underflow and fail to
* decrement when saturated at UINT_MAX.
* decrement when saturated at REFCOUNT_SATURATED.
*
* Provides release memory ordering, such that prior loads and stores are done
* before, and provides a control dependency such that free() must come after.