From patchwork Wed Jun 28 22:52:58 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mark Brown X-Patchwork-Id: 13296412 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id EBDF0EB64DA for ; Wed, 28 Jun 2023 22:53:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229581AbjF1WxW (ORCPT ); Wed, 28 Jun 2023 18:53:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51620 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230413AbjF1WxJ (ORCPT ); Wed, 28 Jun 2023 18:53:09 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 115231FDC for ; Wed, 28 Jun 2023 15:53:08 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id A35DE6147F for ; Wed, 28 Jun 2023 22:53:07 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C8840C433C0; Wed, 28 Jun 2023 22:53:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1687992787; bh=68dGS9oL40E7cxdas87mbb7uykwmjXBlTk6CNaE/6js=; h=From:Date:Subject:To:Cc:From; b=Of9FpDUs+wLlMVvLx52h778prjGxFklP/8n68rg7D+R1QeV4iklucVkkZQCBHZ+zN XsCESndZOsBMEFLSoOvaVx+X1OdJi2sjGrBHRdUXVlVo+Bf76CAiOhNr4mlcBRzlsW qKg5N8lz44lz5m0Tg9pqUx4Wz9273hNggF2iR8UIuvo1s3nG8/FOJy9MCBUZTIGL8h B3XUcjVVcp8gC6QdRVTFr8qCGU4Rap9fVkpau0O845frZLbn+rPFvv0SPSDqiycU6p mQqVasj0FE/frbToHS+oNU/jEQdtJDakv/m5qJxpLkjmxoQ53qaBxcFIUptK522pS1 2OQmFbVOq2IuA== From: Mark Brown Date: Wed, 28 Jun 2023 23:52:58 +0100 Subject: [PATCH] kselftest/arm64: Exit streaming mode after collecting signal context MIME-Version: 1.0 Message-Id: <20230628-arm64-signal-memcpy-fix-v1-1-db3e0300829e@kernel.org> X-B4-Tracking: v=1; b=H4sIAMm5nGQC/x2N3QqDMAxGX0VyvUBth5O9ythFWqOGrVUS2A/iu 6/u8hy+w7eBsQobXJsNlF9ispQK7amBNFOZGGWoDN754DrfI2nuzmgyFXpi5pzWL47ywcvAIYb Uj9Q6qHUkY4xKJc1H/170cehVua7/h7f7vv8A1FwFhoAAAAA= To: Catalin Marinas , Will Deacon , Shuah Khan Cc: linux-arm-kernel@lists.infradead.org, linux-kselftest@vger.kernel.org, Mark Brown X-Mailer: b4 0.13-dev-c6835 X-Developer-Signature: v=1; a=openpgp-sha256; l=3232; i=broonie@kernel.org; h=from:subject:message-id; bh=68dGS9oL40E7cxdas87mbb7uykwmjXBlTk6CNaE/6js=; b=owEBbQGS/pANAwAKASTWi3JdVIfQAcsmYgBknLnQSHo0ow++6DWpt9+O4FILzu3JfJuC9rm1CN0o 5wrrYemJATMEAAEKAB0WIQSt5miqZ1cYtZ/in+ok1otyXVSH0AUCZJy50AAKCRAk1otyXVSH0H2DB/ 4/bkq3fpGQY5GtAM+B7ksIgMK9vV9/3HHOlJ2tYT9YRs3O3L+Pqz4H2C6yjFeRnhnzjG4H9v58f546 rGwA0zwRO61DHwRZVaHfouvKT+gMU+LUTpmJCdb2GJyR+/Ot5fhMWbQYprJdOUy/fc/ZMxEM4gGVn0 WUbSj2iBeLSf6+escBUZ47BX+YNHvqztsxknLT4vVJcY7naNKkOE6UokJFEXK117nU0+cHbHk8cshm WwvvpnVAmRFu1xaauWhqUt+ce/5j6XIxP7/jHN0Mw9sFkFHPegoue9MdE/vbtGxtNccE5X5VdJD7mJ ljDeFpliQ7KOfi+1BKZUbPoAJn7oOx X-Developer-Key: i=broonie@kernel.org; a=openpgp; fpr=3F2568AAC26998F9E813A1C5C3F436CA30F5D8EB Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org When we collect a signal context with one of the SME modes enabled we will have enabled that mode behind the compiler and libc's back so they may issue some instructions not valid in streaming mode, causing spurious failures. For the code prior to issuing the BRK to trigger signal handling we need to stay in streaming mode if we were already there since that's a part of the signal context the caller is trying to collect. Unfortunately this code includes a memset() which is likely to be heavily optimised and is likely to use FP instructions incompatible with streaming mode. We can avoid this happening by open coding the memset(), inserting a volatile assembly statement to avoid the compiler recognising what's being done and doing something in optimisation. This code is not performance critical so the inefficiency should not be an issue. After collecting the context we can simply exit streaming mode, avoiding these issues. Use a full SMSTOP for safety to prevent any issues appearing with ZA. Reported-by: Will Deacon Signed-off-by: Mark Brown --- .../selftests/arm64/signal/test_signals_utils.h | 28 +++++++++++++++++++++- 1 file changed, 27 insertions(+), 1 deletion(-) --- base-commit: 6995e2de6891c724bfeb2db33d7b87775f913ad1 change-id: 20230628-arm64-signal-memcpy-fix-7de3b3c8fa10 Best regards, diff --git a/tools/testing/selftests/arm64/signal/test_signals_utils.h b/tools/testing/selftests/arm64/signal/test_signals_utils.h index 222093f51b67..db28409fd44b 100644 --- a/tools/testing/selftests/arm64/signal/test_signals_utils.h +++ b/tools/testing/selftests/arm64/signal/test_signals_utils.h @@ -60,13 +60,28 @@ static __always_inline bool get_current_context(struct tdescr *td, size_t dest_sz) { static volatile bool seen_already; + int i; + char *uc = (char *)dest_uc; assert(td && dest_uc); /* it's a genuine invocation..reinit */ seen_already = 0; td->live_uc_valid = 0; td->live_sz = dest_sz; - memset(dest_uc, 0x00, td->live_sz); + + /* + * This is a memset() but we don't want the compiler to + * optimise it into either instructions or a library call + * which might be incompatible with streaming mode. + */ + for (i = 0; i < td->live_sz; i++) { + asm volatile("nop" + : "+m" (*dest_uc) + : + : "memory"); + uc[i] = 0; + } + td->live_uc = dest_uc; /* * Grab ucontext_t triggering a SIGTRAP. @@ -103,6 +118,17 @@ static __always_inline bool get_current_context(struct tdescr *td, : : "memory"); + /* + * If we were grabbing a streaming mode context then we may + * have entered streaming mode behind the system's back and + * libc or compiler generated code might decide to do + * something invalid in streaming mode, or potentially even + * the state of ZA. Issue a SMSTOP to exit both now we have + * grabbed the state. + */ + if (td->feats_supported & FEAT_SME) + asm volatile("msr S0_3_C4_C6_3, xzr"); + /* * If we get here with seen_already==1 it implies the td->live_uc * context has been used to get back here....this probably means