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Date: Wed, 28 Jun 2017 09:58:15 -0700
From: tip-bot for Kees Cook <tipbot@...or.com>
To: linux-tip-commits@...r.kernel.org
Cc: arnd@...db.de, manfred@...orfullife.com, davem@...emloft.net,
riel@...hat.com, peterz@...radead.org, ebiggers3@...il.com,
elena.reshetova@...el.com, hpa@...or.com, keescook@...omium.org,
dwindsor@...il.com, jannh@...gle.com, mingo@...nel.org,
gregkh@...uxfoundation.org, serge@...lyn.com, adobriyan@...il.com,
ebiederm@...ssion.com, ishkamiel@...il.com, tglx@...utronix.de,
hch@...radead.org, linux-kernel@...r.kernel.org,
jpoimboe@...hat.com, torvalds@...ux-foundation.org,
akpm@...ux-foundation.org, dave@...olabs.net,
linux-arch@...r.kernel.org, James.Bottomley@...senpartnership.com
Subject: [tip:locking/core] locking/refcount: Create unchecked atomic_t
implementation
Commit-ID: fd25d19f6b8da315332bb75936605fb45d3ea981
Gitweb: http://git.kernel.org/tip/fd25d19f6b8da315332bb75936605fb45d3ea981
Author: Kees Cook <keescook@...omium.org>
AuthorDate: Wed, 21 Jun 2017 13:00:26 -0700
Committer: Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 28 Jun 2017 18:54:46 +0200
locking/refcount: Create unchecked atomic_t implementation
Many subsystems will not use refcount_t unless there is a way to build the
kernel so that there is no regression in speed compared to atomic_t. This
adds CONFIG_REFCOUNT_FULL to enable the full refcount_t implementation
which has the validation but is slightly slower. When not enabled,
refcount_t uses the basic unchecked atomic_t routines, which results in
no code changes compared to just using atomic_t directly.
Signed-off-by: Kees Cook <keescook@...omium.org>
Acked-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Alexey Dobriyan <adobriyan@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Christoph Hellwig <hch@...radead.org>
Cc: David S. Miller <davem@...emloft.net>
Cc: David Windsor <dwindsor@...il.com>
Cc: Davidlohr Bueso <dave@...olabs.net>
Cc: Elena Reshetova <elena.reshetova@...el.com>
Cc: Eric Biggers <ebiggers3@...il.com>
Cc: Eric W. Biederman <ebiederm@...ssion.com>
Cc: Hans Liljestrand <ishkamiel@...il.com>
Cc: James Bottomley <James.Bottomley@...senpartnership.com>
Cc: Jann Horn <jannh@...gle.com>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Manfred Spraul <manfred@...orfullife.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Rik van Riel <riel@...hat.com>
Cc: Serge E. Hallyn <serge@...lyn.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: arozansk@...hat.com
Cc: axboe@...nel.dk
Cc: linux-arch <linux-arch@...r.kernel.org>
Link: http://lkml.kernel.org/r/20170621200026.GA115679@beast
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
arch/Kconfig | 9 +++++++++
include/linux/refcount.h | 42 ++++++++++++++++++++++++++++++++++++++++++
lib/refcount.c | 3 +++
3 files changed, 54 insertions(+)
diff --git a/arch/Kconfig b/arch/Kconfig
index 6c00e5b..f76b214 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -867,4 +867,13 @@ config STRICT_MODULE_RWX
config ARCH_WANT_RELAX_ORDER
bool
+config REFCOUNT_FULL
+ bool "Perform full reference count validation at the expense of speed"
+ help
+ Enabling this switches the refcounting infrastructure from a fast
+ unchecked atomic_t implementation to a fully state checked
+ implementation, which can be (slightly) slower but provides protections
+ against various use-after-free conditions that can be used in
+ security flaw exploits.
+
source "kernel/gcov/Kconfig"
diff --git a/include/linux/refcount.h b/include/linux/refcount.h
index b34aa64..bb71f28 100644
--- a/include/linux/refcount.h
+++ b/include/linux/refcount.h
@@ -41,6 +41,7 @@ static inline unsigned int refcount_read(const refcount_t *r)
return atomic_read(&r->refs);
}
+#ifdef CONFIG_REFCOUNT_FULL
extern __must_check bool refcount_add_not_zero(unsigned int i, refcount_t *r);
extern void refcount_add(unsigned int i, refcount_t *r);
@@ -52,6 +53,47 @@ extern void refcount_sub(unsigned int i, refcount_t *r);
extern __must_check bool refcount_dec_and_test(refcount_t *r);
extern void refcount_dec(refcount_t *r);
+#else
+static inline __must_check bool refcount_add_not_zero(unsigned int i, refcount_t *r)
+{
+ return atomic_add_unless(&r->refs, i, 0);
+}
+
+static inline void refcount_add(unsigned int i, refcount_t *r)
+{
+ atomic_add(i, &r->refs);
+}
+
+static inline __must_check bool refcount_inc_not_zero(refcount_t *r)
+{
+ return atomic_add_unless(&r->refs, 1, 0);
+}
+
+static inline void refcount_inc(refcount_t *r)
+{
+ atomic_inc(&r->refs);
+}
+
+static inline __must_check bool refcount_sub_and_test(unsigned int i, refcount_t *r)
+{
+ return atomic_sub_and_test(i, &r->refs);
+}
+
+static inline void refcount_sub(unsigned int i, refcount_t *r)
+{
+ atomic_sub(i, &r->refs);
+}
+
+static inline __must_check bool refcount_dec_and_test(refcount_t *r)
+{
+ return atomic_dec_and_test(&r->refs);
+}
+
+static inline void refcount_dec(refcount_t *r)
+{
+ atomic_dec(&r->refs);
+}
+#endif /* CONFIG_REFCOUNT_FULL */
extern __must_check bool refcount_dec_if_one(refcount_t *r);
extern __must_check bool refcount_dec_not_one(refcount_t *r);
diff --git a/lib/refcount.c b/lib/refcount.c
index 9f90678..5d0582a 100644
--- a/lib/refcount.c
+++ b/lib/refcount.c
@@ -37,6 +37,8 @@
#include <linux/refcount.h>
#include <linux/bug.h>
+#ifdef CONFIG_REFCOUNT_FULL
+
/**
* refcount_add_not_zero - add a value to a refcount unless it is 0
* @i: the value to add to the refcount
@@ -225,6 +227,7 @@ void refcount_dec(refcount_t *r)
WARN_ONCE(refcount_dec_and_test(r), "refcount_t: decrement hit 0; leaking memory.\n");
}
EXPORT_SYMBOL(refcount_dec);
+#endif /* CONFIG_REFCOUNT_FULL */
/**
* refcount_dec_if_one - decrement a refcount if it is 1
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