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fb041bb7c0
The generic implementation of refcount_t should be good enough for everybody, so remove ARCH_HAS_REFCOUNT and REFCOUNT_FULL entirely, leaving the generic implementation enabled unconditionally. Signed-off-by: Will Deacon <will@kernel.org> Reviewed-by: Ard Biesheuvel <ardb@kernel.org> Acked-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/20191121115902.2551-9-will@kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
187 lines
4.8 KiB
C
187 lines
4.8 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Out-of-line refcount functions.
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*/
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#include <linux/mutex.h>
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#include <linux/refcount.h>
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#include <linux/spinlock.h>
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#include <linux/bug.h>
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#define REFCOUNT_WARN(str) WARN_ONCE(1, "refcount_t: " str ".\n")
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void refcount_warn_saturate(refcount_t *r, enum refcount_saturation_type t)
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{
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refcount_set(r, REFCOUNT_SATURATED);
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switch (t) {
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case REFCOUNT_ADD_NOT_ZERO_OVF:
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REFCOUNT_WARN("saturated; leaking memory");
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break;
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case REFCOUNT_ADD_OVF:
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REFCOUNT_WARN("saturated; leaking memory");
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break;
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case REFCOUNT_ADD_UAF:
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REFCOUNT_WARN("addition on 0; use-after-free");
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break;
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case REFCOUNT_SUB_UAF:
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REFCOUNT_WARN("underflow; use-after-free");
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break;
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case REFCOUNT_DEC_LEAK:
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REFCOUNT_WARN("decrement hit 0; leaking memory");
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break;
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default:
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REFCOUNT_WARN("unknown saturation event!?");
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}
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}
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EXPORT_SYMBOL(refcount_warn_saturate);
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/**
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* refcount_dec_if_one - decrement a refcount if it is 1
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* @r: the refcount
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*
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* No atomic_t counterpart, it attempts a 1 -> 0 transition and returns the
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* success thereof.
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*
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* Like all decrement operations, it provides release memory order and provides
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* a control dependency.
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*
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* It can be used like a try-delete operator; this explicit case is provided
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* and not cmpxchg in generic, because that would allow implementing unsafe
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* operations.
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*
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* Return: true if the resulting refcount is 0, false otherwise
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*/
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bool refcount_dec_if_one(refcount_t *r)
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{
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int val = 1;
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return atomic_try_cmpxchg_release(&r->refs, &val, 0);
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}
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EXPORT_SYMBOL(refcount_dec_if_one);
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/**
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* refcount_dec_not_one - decrement a refcount if it is not 1
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* @r: the refcount
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*
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* No atomic_t counterpart, it decrements unless the value is 1, in which case
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* it will return false.
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*
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* Was often done like: atomic_add_unless(&var, -1, 1)
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*
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* Return: true if the decrement operation was successful, false otherwise
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*/
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bool refcount_dec_not_one(refcount_t *r)
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{
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unsigned int new, val = atomic_read(&r->refs);
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do {
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if (unlikely(val == REFCOUNT_SATURATED))
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return true;
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if (val == 1)
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return false;
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new = val - 1;
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if (new > val) {
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WARN_ONCE(new > val, "refcount_t: underflow; use-after-free.\n");
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return true;
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}
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} while (!atomic_try_cmpxchg_release(&r->refs, &val, new));
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return true;
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}
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EXPORT_SYMBOL(refcount_dec_not_one);
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/**
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* refcount_dec_and_mutex_lock - return holding mutex if able to decrement
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* refcount to 0
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* @r: the refcount
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* @lock: the mutex to be locked
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*
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* Similar to atomic_dec_and_mutex_lock(), it will WARN on underflow and fail
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* to decrement when saturated at REFCOUNT_SATURATED.
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*
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* Provides release memory ordering, such that prior loads and stores are done
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* before, and provides a control dependency such that free() must come after.
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* See the comment on top.
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*
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* Return: true and hold mutex if able to decrement refcount to 0, false
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* otherwise
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*/
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bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock)
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{
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if (refcount_dec_not_one(r))
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return false;
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mutex_lock(lock);
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if (!refcount_dec_and_test(r)) {
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mutex_unlock(lock);
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return false;
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}
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return true;
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}
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EXPORT_SYMBOL(refcount_dec_and_mutex_lock);
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/**
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* refcount_dec_and_lock - return holding spinlock if able to decrement
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* refcount to 0
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* @r: the refcount
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* @lock: the spinlock to be locked
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*
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* Similar to atomic_dec_and_lock(), it will WARN on underflow and fail to
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* decrement when saturated at REFCOUNT_SATURATED.
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*
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* Provides release memory ordering, such that prior loads and stores are done
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* before, and provides a control dependency such that free() must come after.
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* See the comment on top.
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*
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* Return: true and hold spinlock if able to decrement refcount to 0, false
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* otherwise
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*/
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bool refcount_dec_and_lock(refcount_t *r, spinlock_t *lock)
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{
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if (refcount_dec_not_one(r))
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return false;
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spin_lock(lock);
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if (!refcount_dec_and_test(r)) {
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spin_unlock(lock);
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return false;
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}
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return true;
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}
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EXPORT_SYMBOL(refcount_dec_and_lock);
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/**
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* refcount_dec_and_lock_irqsave - return holding spinlock with disabled
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* interrupts if able to decrement refcount to 0
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* @r: the refcount
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* @lock: the spinlock to be locked
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* @flags: saved IRQ-flags if the is acquired
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*
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* Same as refcount_dec_and_lock() above except that the spinlock is acquired
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* with disabled interupts.
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*
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* Return: true and hold spinlock if able to decrement refcount to 0, false
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* otherwise
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*/
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bool refcount_dec_and_lock_irqsave(refcount_t *r, spinlock_t *lock,
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unsigned long *flags)
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{
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if (refcount_dec_not_one(r))
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return false;
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spin_lock_irqsave(lock, *flags);
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if (!refcount_dec_and_test(r)) {
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spin_unlock_irqrestore(lock, *flags);
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return false;
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}
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return true;
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}
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EXPORT_SYMBOL(refcount_dec_and_lock_irqsave);
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