From 102a0743326a03cd1a1202ceda21e175b7d3575c Mon Sep 17 00:00:00 2001
From: hc <hc@nodka.com>
Date: Tue, 20 Feb 2024 01:20:52 +0000
Subject: [PATCH] add new system file
---
kernel/lib/refcount.c | 249 +++++--------------------------------------------
1 files changed, 28 insertions(+), 221 deletions(-)
diff --git a/kernel/lib/refcount.c b/kernel/lib/refcount.c
index ebcf8cd..ebac8b7 100644
--- a/kernel/lib/refcount.c
+++ b/kernel/lib/refcount.c
@@ -1,38 +1,6 @@
// SPDX-License-Identifier: GPL-2.0
/*
- * Variant of atomic_t specialized for reference counts.
- *
- * 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'
- * use-after-free issues.
- *
- * Memory ordering rules are slightly relaxed wrt regular atomic_t functions
- * and provide only what is strictly required for refcounts.
- *
- * The increments are fully relaxed; these will not provide ordering. The
- * rationale is that whatever is used to obtain the object we're increasing the
- * reference count on will provide the ordering. For locked data structures,
- * its the lock acquire, for RCU/lockless data structures its the dependent
- * load.
- *
- * Do note that inc_not_zero() provides a control dependency which will order
- * future stores against the inc, this ensures we'll never modify the object
- * if we did not in fact acquire a reference.
- *
- * The decrements will provide release order, such that all the prior loads and
- * stores will be issued before, it also provides a control dependency, which
- * will order us against the subsequent free().
- *
- * The control dependency is against the load of the cmpxchg (ll/sc) that
- * succeeded. This means the stores aren't fully ordered, but this is fine
- * because the 1->0 transition indicates no concurrency.
- *
- * Note that the allocator is responsible for ordering things between free()
- * and alloc().
- *
+ * Out-of-line refcount functions.
*/
#include <linux/mutex.h>
@@ -40,194 +8,33 @@
#include <linux/spinlock.h>
#include <linux/bug.h>
-/**
- * refcount_add_not_zero_checked - add a value to a refcount unless it is 0
- * @i: the value to add to the refcount
- * @r: the refcount
- *
- * Will saturate at UINT_MAX 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
- * and thereby orders future stores. See the comment on top.
- *
- * Use of this function is not recommended for the normal reference counting
- * use case in which references are taken and released one at a time. In these
- * cases, refcount_inc(), or one of its variants, should instead be used to
- * increment a reference count.
- *
- * Return: false if the passed refcount is 0, true otherwise
- */
-bool refcount_add_not_zero_checked(unsigned int i, refcount_t *r)
+#define REFCOUNT_WARN(str) WARN_ONCE(1, "refcount_t: " str ".\n")
+
+void refcount_warn_saturate(refcount_t *r, enum refcount_saturation_type t)
{
- unsigned int new, val = atomic_read(&r->refs);
+ refcount_set(r, REFCOUNT_SATURATED);
- do {
- if (!val)
- return false;
-
- if (unlikely(val == UINT_MAX))
- return true;
-
- new = val + i;
- if (new < val)
- new = UINT_MAX;
-
- } while (!atomic_try_cmpxchg_relaxed(&r->refs, &val, new));
-
- WARN_ONCE(new == UINT_MAX, "refcount_t: saturated; leaking memory.\n");
-
- return true;
+ switch (t) {
+ case REFCOUNT_ADD_NOT_ZERO_OVF:
+ REFCOUNT_WARN("saturated; leaking memory");
+ break;
+ case REFCOUNT_ADD_OVF:
+ REFCOUNT_WARN("saturated; leaking memory");
+ break;
+ case REFCOUNT_ADD_UAF:
+ REFCOUNT_WARN("addition on 0; use-after-free");
+ break;
+ case REFCOUNT_SUB_UAF:
+ REFCOUNT_WARN("underflow; use-after-free");
+ break;
+ case REFCOUNT_DEC_LEAK:
+ REFCOUNT_WARN("decrement hit 0; leaking memory");
+ break;
+ default:
+ REFCOUNT_WARN("unknown saturation event!?");
+ }
}
-EXPORT_SYMBOL(refcount_add_not_zero_checked);
-
-/**
- * refcount_add_checked - add a value to a refcount
- * @i: the value to add to the refcount
- * @r: the refcount
- *
- * Similar to atomic_add(), but will saturate at UINT_MAX 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
- * and thereby orders future stores. See the comment on top.
- *
- * Use of this function is not recommended for the normal reference counting
- * use case in which references are taken and released one at a time. In these
- * cases, refcount_inc(), or one of its variants, should instead be used to
- * increment a reference count.
- */
-void refcount_add_checked(unsigned int i, refcount_t *r)
-{
- WARN_ONCE(!refcount_add_not_zero_checked(i, r), "refcount_t: addition on 0; use-after-free.\n");
-}
-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.
- *
- * 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
- * and thereby orders future stores. See the comment on top.
- *
- * Return: true if the increment was successful, false otherwise
- */
-bool refcount_inc_not_zero_checked(refcount_t *r)
-{
- unsigned int new, val = atomic_read(&r->refs);
-
- do {
- new = val + 1;
-
- if (!val)
- return false;
-
- if (unlikely(!new))
- return true;
-
- } while (!atomic_try_cmpxchg_relaxed(&r->refs, &val, new));
-
- WARN_ONCE(new == UINT_MAX, "refcount_t: saturated; leaking memory.\n");
-
- return true;
-}
-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.
- *
- * Provides no memory ordering, it is assumed the caller already has a
- * reference on the object.
- *
- * Will WARN if the refcount is 0, as this represents a possible use-after-free
- * condition.
- */
-void refcount_inc_checked(refcount_t *r)
-{
- WARN_ONCE(!refcount_inc_not_zero_checked(r), "refcount_t: increment on 0; use-after-free.\n");
-}
-EXPORT_SYMBOL(refcount_inc_checked);
-
-/**
- * refcount_sub_and_test_checked - subtract from a refcount and test if it is 0
- * @i: amount to subtract from the refcount
- * @r: the refcount
- *
- * 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.
- *
- * Provides release memory ordering, such that prior loads and stores are done
- * before, and provides a control dependency such that free() must come after.
- * See the comment on top.
- *
- * Use of this function is not recommended for the normal reference counting
- * use case in which references are taken and released one at a time. In these
- * cases, refcount_dec(), or one of its variants, should instead be used to
- * decrement a reference count.
- *
- * Return: true if the resulting refcount is 0, false otherwise
- */
-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))
- return false;
-
- new = val - i;
- if (new > val) {
- WARN_ONCE(new > val, "refcount_t: underflow; use-after-free.\n");
- return false;
- }
-
- } while (!atomic_try_cmpxchg_release(&r->refs, &val, new));
-
- return !new;
-}
-EXPORT_SYMBOL(refcount_sub_and_test_checked);
-
-/**
- * refcount_dec_and_test_checked - decrement a refcount and test if it is 0
- * @r: the refcount
- *
- * Similar to atomic_dec_and_test(), it will WARN on underflow and fail to
- * decrement when saturated at UINT_MAX.
- *
- * Provides release memory ordering, such that prior loads and stores are done
- * before, and provides a control dependency such that free() must come after.
- * See the comment on top.
- *
- * Return: true if the resulting refcount is 0, false otherwise
- */
-bool refcount_dec_and_test_checked(refcount_t *r)
-{
- return refcount_sub_and_test_checked(1, r);
-}
-EXPORT_SYMBOL(refcount_dec_and_test_checked);
-
-/**
- * refcount_dec_checked - decrement a refcount
- * @r: the refcount
- *
- * Similar to atomic_dec(), it will WARN on underflow and fail to decrement
- * when saturated at UINT_MAX.
- *
- * Provides release memory ordering, such that prior loads and stores are done
- * before.
- */
-void refcount_dec_checked(refcount_t *r)
-{
- WARN_ONCE(refcount_dec_and_test_checked(r), "refcount_t: decrement hit 0; leaking memory.\n");
-}
-EXPORT_SYMBOL(refcount_dec_checked);
+EXPORT_SYMBOL(refcount_warn_saturate);
/**
* refcount_dec_if_one - decrement a refcount if it is 1
@@ -269,7 +76,7 @@
unsigned int new, val = atomic_read(&r->refs);
do {
- if (unlikely(val == UINT_MAX))
+ if (unlikely(val == REFCOUNT_SATURATED))
return true;
if (val == 1)
@@ -294,7 +101,7 @@
* @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.
@@ -325,7 +132,7 @@
* @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.
--
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