From patchwork Tue Jul 25 13:45:09 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Michael Tokarev X-Patchwork-Id: 1812557 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@legolas.ozlabs.org Authentication-Results: legolas.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org (client-ip=209.51.188.17; helo=lists.gnu.org; envelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org; receiver=) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-ECDSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by legolas.ozlabs.org (Postfix) with ESMTPS id 4R9JLQ4mdqz1ydq for ; Tue, 25 Jul 2023 23:49:49 +1000 (AEST) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qOINo-0008Qu-4x; Tue, 25 Jul 2023 09:47:24 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qOINl-0008KJ-DA; Tue, 25 Jul 2023 09:47:21 -0400 Received: from isrv.corpit.ru ([86.62.121.231]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qOINj-0001gv-HE; Tue, 25 Jul 2023 09:47:21 -0400 Received: from tsrv.corpit.ru (tsrv.tls.msk.ru [192.168.177.2]) by isrv.corpit.ru (Postfix) with ESMTP id 61B0416101; Tue, 25 Jul 2023 16:45:37 +0300 (MSK) Received: from tls.msk.ru (mjt.wg.tls.msk.ru [192.168.177.130]) by tsrv.corpit.ru (Postfix) with SMTP id 07637194C3; Tue, 25 Jul 2023 16:45:35 +0300 (MSK) Received: (nullmailer pid 3370855 invoked by uid 1000); Tue, 25 Jul 2023 13:45:29 -0000 From: Michael Tokarev To: qemu-devel@nongnu.org Cc: qemu-stable@nongnu.org, Jordan Niethe , Anushree Mathur , Michael Tokarev , Richard Henderson , Benjamin Gray Subject: [Stable-8.0.4 24/31] tcg/ppc: Fix race in goto_tb implementation Date: Tue, 25 Jul 2023 16:45:09 +0300 Message-Id: <20230725134517.3370706-24-mjt@tls.msk.ru> X-Mailer: git-send-email 2.39.2 In-Reply-To: References: MIME-Version: 1.0 Received-SPF: pass client-ip=86.62.121.231; envelope-from=mjt@tls.msk.ru; helo=isrv.corpit.ru X-Spam_score_int: -68 X-Spam_score: -6.9 X-Spam_bar: ------ X-Spam_report: (-6.9 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_HI=-5, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org From: Jordan Niethe Commit 20b6643324 ("tcg/ppc: Reorg goto_tb implementation") modified goto_tb to ensure only a single instruction was patched to prevent incorrect behavior if a thread was in the middle of multiple instructions when they were replaced. However this introduced a race between loading the jmp target into TCG_REG_TB and patching and executing the direct branch. The relevant part of the goto_tb implementation: ld TCG_REG_TB, TARGET_ADDR_LOCATION(TCG_REG_TB) patch_location: mtctr TCG_REG_TB bctr tb_target_set_jmp_target() will replace 'patch_location' with a direct branch if the target is in range. The direct branch now relies on TCG_REG_TB being set up correctly by the ld. Prior to this commit multiple instructions were patched in for the direct branch case; these instructions would initialize TCG_REG_TB to the same value as the branch target. Imagine the following sequence: 1) Thread A is executing the goto_tb sequence and loads the jmp target into TCG_REG_TB. 2) Thread B updates the jmp target address and calls tb_target_set_jmp_target(). This patches a new direct branch into the goto_tb sequence. 3) Thread A executes the newly patched direct branch. The value in TCG_REG_TB still contains the old jmp target. TCG_REG_TB MUST contain the translation block's tc.ptr. Execution will eventually crash after performing memory accesses generated from a faulty value in TCG_REG_TB. This presents as segfaults or illegal instruction exceptions. Do not revert commit 20b6643324 as it did fix a different race condition. Instead remove the direct branch optimization and always use indirect branches. The direct branch optimization can be re-added later with a race free sequence. Fixes: 20b6643324 ("tcg/ppc: Reorg goto_tb implementation") Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1726 Reported-by: Anushree Mathur Tested-by: Anushree Mathur Tested-by: Michael Tokarev Reviewed-by: Richard Henderson Co-developed-by: Benjamin Gray Signed-off-by: Jordan Niethe Signed-off-by: Benjamin Gray Message-Id: <20230717093001.13167-1-jniethe5@gmail.com> (cherry picked from commit 736a1588c104e9995c1831df33554df1f1def8b8) Signed-off-by: Michael Tokarev diff --git a/tcg/ppc/tcg-target.c.inc b/tcg/ppc/tcg-target.c.inc index 066b49224a..c68bf08e38 100644 --- a/tcg/ppc/tcg-target.c.inc +++ b/tcg/ppc/tcg-target.c.inc @@ -2546,11 +2546,10 @@ static void tcg_out_goto_tb(TCGContext *s, int which) ptrdiff_t offset = tcg_tbrel_diff(s, (void *)ptr); tcg_out_mem_long(s, LD, LDX, TCG_REG_TB, TCG_REG_TB, offset); - /* Direct branch will be patched by tb_target_set_jmp_target. */ + /* TODO: Use direct branches when possible. */ set_jmp_insn_offset(s, which); tcg_out32(s, MTSPR | RS(TCG_REG_TB) | CTR); - /* When branch is out of range, fall through to indirect. */ tcg_out32(s, BCCTR | BO_ALWAYS); /* For the unlinked case, need to reset TCG_REG_TB. */ @@ -2578,10 +2577,12 @@ void tb_target_set_jmp_target(const TranslationBlock *tb, int n, intptr_t diff = addr - jmp_rx; tcg_insn_unit insn; + if (USE_REG_TB) { + return; + } + if (in_range_b(diff)) { insn = B | (diff & 0x3fffffc); - } else if (USE_REG_TB) { - insn = MTSPR | RS(TCG_REG_TB) | CTR; } else { insn = NOP; }