linux-kernel - Re: [PATCH] locking/barriers: evaluate the argument to lockless

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20160614105038.GC30921@twins.programming.kicks-ass.net>
Date:	Tue, 14 Jun 2016 12:50:38 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mateusz Guzik <mguzik@...hat.com>
Cc:	linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...nel.org,
	hpa@...or.com, torvalds@...ux-foundation.org
Subject: Re: [PATCH] locking/barriers: evaluate the argument to
 lockless_dereference only once

On Tue, Jun 07, 2016 at 03:14:55PM +0200, Mateusz Guzik wrote:
> The commit 25841ee0e9d2a ("Validate lockless_dereference() is used on a
> pointer type") added a second use of the parameter to the macro.
> 
> This leads to trouble with consumers which use arguments with side
> effects.

Current tip/locking/core doesn't have that patch anymore IIRC, Ingo
folded your thing and we now have:


commit 331b6d8c7afc2e5b900b9dcd850c265e1ba8d8e7
Author: Peter Zijlstra <peterz@...radead.org>
Date:   Sun May 22 12:48:27 2016 +0200

    locking/barriers: Validate lockless_dereference() is used on a pointer type
    
    Use the type to validate the argument @p is indeed a pointer type.
    
    Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
    Cc: Alexey Dobriyan <adobriyan@...il.com>
    Cc: Andrew Morton <akpm@...ux-foundation.org>
    Cc: Linus Torvalds <torvalds@...ux-foundation.org>
    Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
    Cc: Paul McKenney <paulmck@...ux.vnet.ibm.com>
    Cc: Peter Zijlstra <peterz@...radead.org>
    Cc: Thomas Gleixner <tglx@...utronix.de>
    Link: http://lkml.kernel.org/r/20160522104827.GP3193@twins.programming.kicks-ass.net
    Signed-off-by: Ingo Molnar <mingo@...nel.org>

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 793c0829e3a3..06f27fd9d760 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -545,10 +545,14 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
  * Similar to rcu_dereference(), but for situations where the pointed-to
  * object's lifetime is managed by something other than RCU.  That
  * "something other" might be reference counting or simple immortality.
+ *
+ * The seemingly unused void * variable is to validate @p is indeed a pointer
+ * type. All pointer types silently cast to void *.
  */
 #define lockless_dereference(p) \
 ({ \
 	typeof(p) _________p1 = READ_ONCE(p); \
+	__maybe_unused const void * const _________p2 = _________p1; \
 	smp_read_barrier_depends(); /* Dependency order vs. p above. */ \
 	(_________p1); \
 })