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[2620:137:e000::1:20]) by mx.google.com with ESMTP id l7-20020a635707000000b0043aa67c7d8esi3874793pgb.738.2022.11.04.00.28.58; Fri, 04 Nov 2022 00:29:11 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=nju.edu.cn Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231324AbiKDH0S (ORCPT + 99 others); Fri, 4 Nov 2022 03:26:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53090 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229779AbiKDH0Q (ORCPT ); Fri, 4 Nov 2022 03:26:16 -0400 Received: from smtpbgeu2.qq.com (smtpbgeu2.qq.com [18.194.254.142]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2176518363; Fri, 4 Nov 2022 00:26:08 -0700 (PDT) X-QQ-mid: bizesmtp75t1667546649tv9fay8q Received: from localhost.localdomain ( [58.213.8.169]) by bizesmtp.qq.com (ESMTP) with id ; Fri, 04 Nov 2022 15:24:08 +0800 (CST) X-QQ-SSF: 0140000000000030B000000A0000000 X-QQ-FEAT: FVl8EHhfVR5sZRNRY9/DeJL8TZ/JzmaTzPbfcQeUkmkwgHG3TgzG7YguMkqwy yaQfw+EnjutXfftW/VCbeBl/TfaZCKBW2+Tai+grdWNRQ7bVMqRo8eL5hj9XDxKwdnWVJa4 3xp1I/AsLqrRDSXgrca14LAlBItPg97/+NoX/VhKn3jX2MiM0qBumuYrJx8lkRKC4kNRKY9 PfgdnibQfjejhJ+eZZQkH71Qc4KY5e0m0y9gvNbDdeLcu9lW97h4P1sz051DZacDRatllrx bJWCDDK7cMDQ6rmSheAYzwzwahFpX4UL85BoK2x8Mni1J9E3ASq/Va5D7FUW42JeNQ/O/MS zEFNu67stA7otbGcPr/cJY/mlSuvovGkzZlA2pvnM944vlf/Okkl2i7p57MPTaKMyRWQR9M X-QQ-GoodBg: 1 From: Kunbo Zhang To: dmitry.torokhov@gmail.com, tiwai@suse.de, wsa+renesas@sang-engineering.com Cc: linux-kernel@vger.kernel.org, linux-input@vger.kernel.org, security@kernel.org, Kunbo Zhang Subject: [PATCH] input: i8042 - fix a double-fetch vulnerability introduced by GCC Date: Fri, 4 Nov 2022 15:23:47 +0800 Message-Id: <20221104072347.74314-1-absoler@smail.nju.edu.cn> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 X-QQ-SENDSIZE: 520 Feedback-ID: bizesmtp:smail.nju.edu.cn:qybglogicsvr:qybglogicsvr6 X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,RCVD_IN_DNSWL_NONE, SPF_PASS,T_SPF_HELO_TEMPERROR autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1748549712177172953?= X-GMAIL-MSGID: =?utf-8?q?1748549712177172953?= We found GCC (at least 9.4.0 and 12.1) introduces a double-fetch of `i8042_ports[I8042_AUX_PORT_NO].serio` at drivers/input/serio/i8042.c:408. One comparison of the global variable `i8042_ports[I8042_AUX_PORT_NO].serio` has been compiled to three ones, and thus two extra fetches are introduced. As in the source code, the global variable is tested (at line 408) before three assignments of irq_bit, disable_bit and port_name. However, as shown in the following disassembly of i8042_port_close(), the variable (0x0(%rip)) is fetched and tested three times for each assignment of irq_bit, disable_bit and port_name. 0000000000000e50 : i8042_port_close(): ./drivers/input/serio/i8042.c:408 e50: 48 39 3d 00 00 00 00 cmp %rdi,0x0(%rip) # first load ./drivers/input/serio/i8042.c:403 e57: 41 54 push %r12 ./drivers/input/serio/i8042.c:408 e59: b8 ef ff ff ff mov $0xffffffef,%eax e5e: 49 c7 c4 00 00 00 00 mov $0x0,%r12 ./drivers/input/serio/i8042.c:403 e65: 55 push %rbp ./drivers/input/serio/i8042.c:408 e66: 48 c7 c2 00 00 00 00 mov $0x0,%rdx ./drivers/input/serio/i8042.c:419 e6d: be 60 10 00 00 mov $0x1060,%esi ./drivers/input/serio/i8042.c:403 e72: 53 push %rbx ./drivers/input/serio/i8042.c:408 e73: bb df ff ff ff mov $0xffffffdf,%ebx e78: 0f 45 d8 cmovne %eax,%ebx e7b: 0f 95 c0 setne %al e7e: 83 e8 03 sub $0x3,%eax e81: 48 39 3d 00 00 00 00 cmp %rdi,0x0(%rip) # second load e88: 40 0f 94 c5 sete %bpl e8c: 83 c5 01 add $0x1,%ebp e8f: 48 39 3d 00 00 00 00 cmp %rdi,0x0(%rip) # third load ./drivers/input/serio/i8042.c:419 e96: 48 c7 c7 00 00 00 00 mov $0x0,%rdi ./drivers/input/serio/i8042.c:408 e9d: 4c 0f 45 e2 cmovne %rdx,%r12 We have not found any lock protection for the three fetches of `i8042_ports[I8042_AUX_PORT_NO].serio` yet. If the value of this global variable is modified concurrently among the three fetches, the corresponding assignment of disable_bit or port_name will possibly be incorrect. This patch fixs this by saving the checked value in advance and using a barrier() to prevent compiler optimizations. This is inspired by a similar compiler-introduced double fetch situation [1] in driver/xen (?). [1] GitHub link of commit <8135cf8b092723dbfcc611fe6fdcb3a36c9951c5> ( Save xen_pci_op commands before processing it ) --- drivers/input/serio/i8042.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) Signed-off-by: Kunbo Zhang diff --git a/drivers/input/serio/i8042.c b/drivers/input/serio/i8042.c index f9486495baef..554a2340ca84 100644 --- a/drivers/input/serio/i8042.c +++ b/drivers/input/serio/i8042.c @@ -405,7 +405,9 @@ static void i8042_port_close(struct serio *serio) int disable_bit; const char *port_name; - if (serio == i8042_ports[I8042_AUX_PORT_NO].serio) { + struct serio *tmp = i8042_ports[I8042_AUX_PORT_NO].serio; + barrier(); + if (serio == tmp) { irq_bit = I8042_CTR_AUXINT; disable_bit = I8042_CTR_AUXDIS; port_name = "AUX";