From patchwork Wed Jul 7 08:30:32 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mark Rutland X-Patchwork-Id: 1501629 Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Authentication-Results: ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=vger.kernel.org (client-ip=23.128.96.18; helo=vger.kernel.org; envelope-from=sparclinux-owner@vger.kernel.org; receiver=) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by ozlabs.org (Postfix) with ESMTP id 4GKXgL6Wq3z9sjD for ; Wed, 7 Jul 2021 18:30:38 +1000 (AEST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230126AbhGGIdS (ORCPT ); Wed, 7 Jul 2021 04:33:18 -0400 Received: from foss.arm.com ([217.140.110.172]:59714 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230109AbhGGIdR (ORCPT ); Wed, 7 Jul 2021 04:33:17 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id B58CBED1; Wed, 7 Jul 2021 01:30:37 -0700 (PDT) Received: from lakrids.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id CF5683F694; Wed, 7 Jul 2021 01:30:36 -0700 (PDT) From: Mark Rutland To: linux-kernel@vger.kernel.org, peterz@lists.infradead.org, davem@davemloft.net Cc: Mark Rutland , Ingo Molnar , sparclinux@vger.kernel.org Subject: [PATCH] locking/atomic: sparc: fix arch_cmpxchg64_local() Date: Wed, 7 Jul 2021 09:30:32 +0100 Message-Id: <20210707083032.567-1-mark.rutland@arm.com> X-Mailer: git-send-email 2.11.0 Precedence: bulk List-ID: X-Mailing-List: sparclinux@vger.kernel.org Anatoly reports that since commit: ff5b4f1ed580c59d ("locking/atomic: sparc: move to ARCH_ATOMIC") ... it's possible to reliably trigger an oops by running: stress-ng -v --mmap 1 -t 30s ... which results in a NULL pointer dereference in __split_huge_pmd_locked(). The underlying problem is that commit ff5b4f1ed580c59d left arch_cmpxchg64_local() defined in terms of cmpxchg_local() rather than arch_cmpxchg_local(). In we wrap these with macros which use identically-named variables. When cmpxchg_local() nests inside cmpxchg64_local(), this casues it to use an unitialized variable as the pointer, which can be NULL. This can also be seen in pmdp_establish(), where the compiler can generate the pointer with a `clr` instruction: 0000000000000360 : 360: 9d e3 bf 50 save %sp, -176, %sp 364: fa 5e 80 00 ldx [ %i2 ], %i5 368: 82 10 00 1b mov %i3, %g1 36c: 84 10 20 00 clr %g2 370: c3 f0 90 1d casx [ %g2 ], %i5, %g1 374: 80 a7 40 01 cmp %i5, %g1 378: 32 6f ff fc bne,a %xcc, 368 37c: fa 5e 80 00 ldx [ %i2 ], %i5 380: d0 5e 20 40 ldx [ %i0 + 0x40 ], %o0 384: 96 10 00 1b mov %i3, %o3 388: 94 10 00 1d mov %i5, %o2 38c: 92 10 00 19 mov %i1, %o1 390: 7f ff ff 84 call 1a0 <__set_pmd_acct> 394: b0 10 00 1d mov %i5, %i0 398: 81 cf e0 08 return %i7 + 8 39c: 01 00 00 00 nop This patch fixes the problem by defining arch_cmpxchg64_local() in terms of arch_cmpxchg_local(), avoiding potential shadowing, and resulting in working cmpxchg64_local() and variants, e.g. 0000000000000360 : 360: 9d e3 bf 50 save %sp, -176, %sp 364: fa 5e 80 00 ldx [ %i2 ], %i5 368: 82 10 00 1b mov %i3, %g1 36c: c3 f6 90 1d casx [ %i2 ], %i5, %g1 370: 80 a7 40 01 cmp %i5, %g1 374: 32 6f ff fd bne,a %xcc, 368 378: fa 5e 80 00 ldx [ %i2 ], %i5 37c: d0 5e 20 40 ldx [ %i0 + 0x40 ], %o0 380: 96 10 00 1b mov %i3, %o3 384: 94 10 00 1d mov %i5, %o2 388: 92 10 00 19 mov %i1, %o1 38c: 7f ff ff 85 call 1a0 <__set_pmd_acct> 390: b0 10 00 1d mov %i5, %i0 394: 81 cf e0 08 return %i7 + 8 398: 01 00 00 00 nop 39c: 01 00 00 00 nop Link: https://lore.kernel.org/r/CADxRZqzcrnSMzy50T+kWb_mQVguWDCMu6RoXsCc+-fNDPYXbaw@mail.gmail.com Fixes: ff5b4f1ed580c59d ("locking/atomic: sparc: move to ARCH_ATOMIC") Signed-off-by: Mark Rutland Reported-by: Anatoly Pugachev Tested-by: Anatoly Pugachev Cc: David S. Miller Cc: Ingo Molnar Cc: Peter Zijlstra Cc: sparclinux@vger.kernel.org --- arch/sparc/include/asm/cmpxchg_64.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) Peter, David, could one of you please apply this? It's an urgent fix for fallout from the ARCH_ATOMIC conversion, and it'd be good to fix before -rc1. Thanks, Mark. diff --git a/arch/sparc/include/asm/cmpxchg_64.h b/arch/sparc/include/asm/cmpxchg_64.h index 8c39a9981187..12d00a42c0a3 100644 --- a/arch/sparc/include/asm/cmpxchg_64.h +++ b/arch/sparc/include/asm/cmpxchg_64.h @@ -201,7 +201,7 @@ static inline unsigned long __cmpxchg_local(volatile void *ptr, #define arch_cmpxchg64_local(ptr, o, n) \ ({ \ BUILD_BUG_ON(sizeof(*(ptr)) != 8); \ - cmpxchg_local((ptr), (o), (n)); \ + arch_cmpxchg_local((ptr), (o), (n)); \ }) #define arch_cmpxchg64(ptr, o, n) arch_cmpxchg64_local((ptr), (o), (n))