From patchwork Tue Feb 7 23:56:34 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Windsor X-Patchwork-Id: 9561535 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 651BE60212 for ; Tue, 7 Feb 2017 23:56:57 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 4DADA28415 for ; Tue, 7 Feb 2017 23:56:57 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 3F75528434; Tue, 7 Feb 2017 23:56:57 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.1 required=2.0 tests=BAYES_00, DKIM_ADSP_CUSTOM_MED, DKIM_SIGNED, FREEMAIL_FROM, RCVD_IN_DNSWL_MED, T_DKIM_INVALID autolearn=ham version=3.3.1 Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.wl.linuxfoundation.org (Postfix) with SMTP id 0D92128415 for ; Tue, 7 Feb 2017 23:56:55 +0000 (UTC) Received: (qmail 7655 invoked by uid 550); 7 Feb 2017 23:56:53 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Delivered-To: mailing list kernel-hardening@lists.openwall.com Received: (qmail 7626 invoked from network); 7 Feb 2017 23:56:52 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id; bh=H/8ct7s9K1EXh4ZsRje2eu9T4Dp/TAs2pakUGGDzi60=; b=b9EBqmhRz6o5Fz74/cDH8edJVKx2m+uZb6AApSzjOQF/kuzaf4EsV7xdJh3WRcdYJ4 jZwnUl+yQn2NlfZOLYhuxBsg+QP34+ArnI8NspoHmQh+4bGMhMttU57hQg26m/RQpneF Tz8erT6V+zeNbjjGCqxIBrU9PeHGkdw+dKx1L/RzACXhq8XWoO63FUpcpPdRs3WrBHpm N+hODrLyQYqZ8/Eh8li/vqO3mX0+d4v8+0WX0cwranIprBv20+5Eek3v44SEjFhr0Nv/ HvO3Mhkb46NyKQbYHbzNoCODLVEqyTQM91EUI9KNcVjPLslwdO9RFB/JpAGqFd5ntm7n sQxQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id; bh=H/8ct7s9K1EXh4ZsRje2eu9T4Dp/TAs2pakUGGDzi60=; b=YfJrBEPbtWDfZao302rAhcIhShSkBPp7xt+vq7T6H/MGk3OoXYEPpe50dWxgABEDdt LytCV3TRU77GrmQ15IZ9rK+zSzN8tKtYNPL9o9zuCjhpreOrHi81szmOWT0m0sWgzF1m ivVpPp671blOFo8/DUXkMSIt3LfR7RJ95WvaeoH2ZhR0xNPRbRc95cmjmP2hUuaWs5ob nmNgFMD+q0cj94VLdf2CoyMqaZ5IZTjeNs/JumSfAiQkcQ3Q6xLKOwHWeabqpq8kS3aO Qt1eykRyHJEOVuMgAGDETNGHZD6uBQiNagVYGG5TkbSsoDvRdI5f+8c8DSQqLIjLwD62 q+Zg== X-Gm-Message-State: AMke39lljFin4F6BGfY4T0SkaMQNOcsjzRHiiTY+w7SBdXDk21rBve0qTIYWuuKBUbVsrA== X-Received: by 10.237.53.162 with SMTP id c31mr18296890qte.55.1486511800386; Tue, 07 Feb 2017 15:56:40 -0800 (PST) From: David Windsor To: kernel-hardening@lists.openwall.com, peterz@infradead.org, elena.reshetova@intel.com Cc: keescook@chromium.org, dwindsor@gmail.com, ishkamiel@gmail.com Date: Tue, 7 Feb 2017 18:56:34 -0500 Message-Id: <1486511794-14490-1-git-send-email-dwindsor@gmail.com> X-Mailer: git-send-email 2.7.4 Subject: [kernel-hardening] [PATCH] refcount: add refcount_t API kernel-doc comments X-Virus-Scanned: ClamAV using ClamSMTP This adds kernel-doc comments for the new refcount_t API. Additional feature documentation can go in Documentation/security, if needed. --- include/linux/refcount.h | 110 +++++++++++++++++++++++++++++++++++++++++++---- 1 file changed, 102 insertions(+), 8 deletions(-) diff --git a/include/linux/refcount.h b/include/linux/refcount.h index fc5abdb..ba5a0214 100644 --- a/include/linux/refcount.h +++ b/include/linux/refcount.h @@ -42,22 +42,51 @@ #include #include +/** + * 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 + * there. This avoids wrapping the counter and causing 'spurious' + * use-after-free issues. + */ typedef struct refcount_struct { atomic_t refs; } refcount_t; #define REFCOUNT_INIT(n) { .refs = ATOMIC_INIT(n), } +/** + * refcount_set - set a refcount's internal counter + * @r: the refcount + * @n: value to which internal counter will be set + */ static inline void refcount_set(refcount_t *r, unsigned int n) { atomic_set(&r->refs, n); } +/** + * refcount_read - get a refcount's internal counter + * @r: the refcount + * + * Return: the value of the refcount's internal counter + */ static inline unsigned int refcount_read(const refcount_t *r) { return atomic_read(&r->refs); } + +/** + * refcount_add_not_zero - add a value to a refcount unless the refcount is 0 + * @i: the value to add to the refcount + * @r: the refcount + * + * Will saturate at UINT_MAX and WARN. + * + * Return: false if the refcount is 0, true otherwise. + */ static inline __must_check bool refcount_add_not_zero(unsigned int i, refcount_t *r) { @@ -85,12 +114,17 @@ bool refcount_add_not_zero(unsigned int i, refcount_t *r) return true; } -/* +/** + * refcount_inc_not_zero - increment a refcount unless it is 0 + * @r: the refcount to increment + * * Similar to atomic_inc_not_zero(), 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: false if the refcount is 0, true otherwise */ static inline __must_check bool refcount_inc_not_zero(refcount_t *r) @@ -98,29 +132,49 @@ bool refcount_inc_not_zero(refcount_t *r) return refcount_add_not_zero(1, r); } -/* +/** + * refcount_inc - increment a refcount + * @r: the refcount to increment + * * Similar to atomic_inc(), 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 when this is not so. + * + * Will WARN if refcount is 0. */ static inline void refcount_inc(refcount_t *r) { WARN(!refcount_inc_not_zero(r), "refcount_t: increment on 0; use-after-free.\n"); } +/** + * refcount_add - add a value to a refcount + * @i: the value to add to the refcount + * @r: the refcount + * + * Similar to atomic_add(), will saturate at UINT_MAX and WARN. + */ static inline void refcount_add(unsigned int i, refcount_t *r) { WARN(!refcount_add_not_zero(i, r), "refcount_t: addition on 0; use-after-free.\n"); } -/* +/** + * refcount_sub_and_test - 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(), 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 greater than 0, false if the + * resulting refcount is 0, the refcount's initial value is UINT_MAX + * or the subtraction operation causes an underflow. */ static inline __must_check bool refcount_sub_and_test(unsigned int i, refcount_t *r) @@ -145,13 +199,27 @@ bool refcount_sub_and_test(unsigned int i, refcount_t *r) return !new; } +/** + * refcount_dec_and_test - 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. + * + * Return: true if the resulting refcount is greater than 0, false if the + * resulting refcount is 0, the refcount's initial value is UINT_MAX + * or the decrement operation causes an underflow. + */ static inline __must_check bool refcount_dec_and_test(refcount_t *r) { return refcount_sub_and_test(1, r); } -/* +/** + * refcount_dec - decrement a refcount + * @r: the refcount + * * Similar to atomic_dec(), it will WARN on underflow and fail to decrement * when saturated at UINT_MAX. * @@ -164,7 +232,10 @@ void refcount_dec(refcount_t *r) WARN(refcount_dec_and_test(r), "refcount_t: decrement hit 0; leaking memory.\n"); } -/* +/** + * refcount_dec_if_one - decrement a refcount if it is 1 + * @r: the refcount + * * No atomic_t counterpart, it attempts a 1 -> 0 transition and returns the * success thereof. * @@ -174,6 +245,8 @@ void refcount_dec(refcount_t *r) * It can be used like a try-delete operator; this explicit case is provided * and not cmpxchg in generic, because that would allow implementing unsafe * operations. + * + * Return: true if the refcount was decremented, false otherwise */ static inline __must_check bool refcount_dec_if_one(refcount_t *r) @@ -181,11 +254,16 @@ bool refcount_dec_if_one(refcount_t *r) return atomic_cmpxchg_release(&r->refs, 1, 0) == 1; } -/* +/** + * refcount_dec_not_one - decrement a refcount if it is not 1 + * @r: the refcount + * * No atomic_t counterpart, it decrements unless the value is 1, in which case * it will return false. * * Was often done like: atomic_add_unless(&var, -1, 1) + * + * Return: false if the refcount was 1, true otherwise */ static inline __must_check bool refcount_dec_not_one(refcount_t *r) @@ -213,13 +291,21 @@ bool refcount_dec_not_one(refcount_t *r) return true; } -/* +/** + * refcount_dec_and_mutex_lock - return holding mutex if able to decrement + * refcount to 0 + * @r: the refcount + * @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. * * 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 and hold lock if able to decrement refcount to 0, false + * otherwise */ static inline __must_check bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock) @@ -236,13 +322,21 @@ bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock) return true; } -/* +/** + * refcount_dec_and_lock - return holding spinlock if able to decrement + * refcount to 0 + * @r: the refcount + * @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. * * 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 and hold lock if able to decrement refcount to 0, false + * otherwise */ static inline __must_check bool refcount_dec_and_lock(refcount_t *r, spinlock_t *lock)