From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-28.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 69C76C433E0 for ; Sat, 27 Feb 2021 04:34:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2BE1164E4B for ; Sat, 27 Feb 2021 04:34:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230010AbhB0Edo (ORCPT ); Fri, 26 Feb 2021 23:33:44 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34312 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229795AbhB0Edl (ORCPT ); Fri, 26 Feb 2021 23:33:41 -0500 Received: from mail-pg1-x52e.google.com (mail-pg1-x52e.google.com [IPv6:2607:f8b0:4864:20::52e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AFC80C06174A for ; Fri, 26 Feb 2021 20:33:01 -0800 (PST) Received: by mail-pg1-x52e.google.com with SMTP id h4so7442395pgf.13 for ; Fri, 26 Feb 2021 20:33:01 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=acGrNbfX1ONJlBYzGoeWien8tX1BAEMbXbxus24dvo4=; b=VwhYGS10gHHtx4bHrQ+wdwiMVGIFYdndXhNbDSfz8LMNKUZDsxDS77KcBXcM48iDsf 9Yx4pIOReijOyL27CHIKdm8BwvkfjeEYo9cDnsBzlVmT7Ox1+zJUDuXeWPtcn1d8D7dS NjIRO1lR9xVX6PnAd2pqMx6+nfu0y2yeWfL9J6XBE50qTOjiwP8sppW9V8NxCvMW/Pmi hXh3f/58KJZhyZKf7TTCoQP9cDYdD0AGueo9F6F1MhCKkTcjlvmOVTVoXGLxP+W+uXaF I6kOux4osK/cQG/fBojEJSHumtDiGPajb8aGeeBidUi7StBiFkkxhioNoOmFhDcAHY/O ImIA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=acGrNbfX1ONJlBYzGoeWien8tX1BAEMbXbxus24dvo4=; b=D/GEVqQp5mztatGfgPPZdmWXyZOYyelg+u/Uk0AuB8vpLp3Vx0SIXvedI4AXdW7Lbm tIyPBkhk50khL1Mdaq3Aq+5tELqsLAPiF8xB9b8Pr6y1ynq9nC7hgFIj72Gm25iKa+0R 70ZH5RLcsIxATplcRI2Eubz3MZppNje8yAUKCeorcepH8bkbB1tnvUUtUOWgUH1nY04U 6lzWIKGUbIJJI/m2qujlGkJ8yJyPGxZHBlvwWnJLLdKt4IEEoprIF2dUuNvHbT9V4xqh DVUDbPnFRAX0gUco7T0VGoziB5cim0yeu5+I6/MvtRM/dsXaHJOeiumkJGSeGUNOpdOD RiMg== X-Gm-Message-State: AOAM530m6f8hReadPLN8OKmPauP6TuZhlSjsn5/S6hRImMTUWJ12xlJ9 hptf2LYJw28W4q+XIqQLC1rHRQ== X-Google-Smtp-Source: ABdhPJz7f04Lrx3tfHHrsCRXLLVkuuTouZTHKhhx2qi6IMSYDexUKG5EZ6UhtonHmgDkT+l9SID3fg== X-Received: by 2002:a63:a22:: with SMTP id 34mr5663613pgk.328.1614400380990; Fri, 26 Feb 2021 20:33:00 -0800 (PST) Received: from google.com ([2620:15c:2ce:0:48ad:d4d0:f627:c01f]) by smtp.gmail.com with ESMTPSA id v5sm10761519pfc.100.2021.02.26.20.32.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 26 Feb 2021 20:33:00 -0800 (PST) Date: Fri, 26 Feb 2021 20:32:57 -0800 From: Fangrui Song To: Kees Cook Cc: Arnd Bergmann , Catalin Marinas , Will Deacon , Arnd Bergmann , Ard Biesheuvel , Mark Rutland , Marc Zyngier , David Brazdil , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] arm64: vmlinux.lds.S: keep .entry.tramp.text section Message-ID: <20210227043257.k3aernmnzsvitp7c@google.com> References: <20210226140352.3477860-1-arnd@kernel.org> <202102261256.AF256702@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <202102261256.AF256702@keescook> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021-02-26, Kees Cook wrote: >On Fri, Feb 26, 2021 at 03:03:39PM +0100, Arnd Bergmann wrote: >> From: Arnd Bergmann >> >> When building with CONFIG_LD_DEAD_CODE_DATA_ELIMINATION, >> I sometimes see an assertion >> >> ld.lld: error: Entry trampoline text too big > >Heh, "too big" seems a weird report for having it discarded. :) > >Any idea on this Fangrui? > >( I see this is https://github.com/ClangBuiltLinux/linux/issues/1311 ) This diagnostic is from an ASSERT in arch/arm64/kernel/vmlinux.lds ASSERT((__entry_tramp_text_end - __entry_tramp_text_start) == (1 << 16), "Entry trampoline text too big") In our case (aarch64-linux-gnu-ld or LLD, --gc-sections), all the input sections with this name are discarded, so the output section is either absent (GNU ld) or empty (LLD). KEEP makes the sections GC roots, and it is appropriate to use here. However, I worry that many other KEEP keywords in vmlinux.lds are unnecessary: https://lore.kernel.org/linux-arm-kernel/20210226211323.arkvjnr4hifxapqu@google.com/ git log -S KEEP -- include/asm-generic/vmlinux.lds.h => there is quite a bit unjustified usage. Sure, adding KEEP (GC root) is easy and works around problems, but it not good for CONFIG_LD_DEAD_CODE_DATA_ELIMINATION. Reviewed-by: Fangrui Song > >> >> This happens when any reference to the trampoline is discarded at link >> time. Marking the section as KEEP() avoids the assertion, but I have >> not figured out whether this is the correct solution for the underlying >> problem. >> >> Signed-off-by: Arnd Bergmann > >As a work-around, it seems fine to me. > >Reviewed-by: Kees Cook > >-Kees > >> --- >> arch/arm64/kernel/vmlinux.lds.S | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S >> index 926cdb597a45..c5ee9d5842db 100644 >> --- a/arch/arm64/kernel/vmlinux.lds.S >> +++ b/arch/arm64/kernel/vmlinux.lds.S >> @@ -96,7 +96,7 @@ jiffies = jiffies_64; >> #define TRAMP_TEXT \ >> . = ALIGN(PAGE_SIZE); \ >> __entry_tramp_text_start = .; \ >> - *(.entry.tramp.text) \ >> + KEEP(*(.entry.tramp.text)) \ >> . = ALIGN(PAGE_SIZE); \ >> __entry_tramp_text_end = .; >> #else >> -- >> 2.29.2 >> > >-- >Kees Cook From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_ADSP_CUSTOM_MED,DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E4D2BC433E0 for ; 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Fri, 26 Feb 2021 20:33:00 -0800 (PST) Received: from google.com ([2620:15c:2ce:0:48ad:d4d0:f627:c01f]) by smtp.gmail.com with ESMTPSA id v5sm10761519pfc.100.2021.02.26.20.32.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 26 Feb 2021 20:33:00 -0800 (PST) Date: Fri, 26 Feb 2021 20:32:57 -0800 From: Fangrui Song To: Kees Cook Subject: Re: [PATCH] arm64: vmlinux.lds.S: keep .entry.tramp.text section Message-ID: <20210227043257.k3aernmnzsvitp7c@google.com> References: <20210226140352.3477860-1-arnd@kernel.org> <202102261256.AF256702@keescook> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <202102261256.AF256702@keescook> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210226_233306_673925_59569462 X-CRM114-Status: GOOD ( 22.13 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Arnd Bergmann , Arnd Bergmann , Catalin Marinas , linux-kernel@vger.kernel.org, Marc Zyngier , David Brazdil , Will Deacon , Ard Biesheuvel , linux-arm-kernel@lists.infradead.org Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2021-02-26, Kees Cook wrote: >On Fri, Feb 26, 2021 at 03:03:39PM +0100, Arnd Bergmann wrote: >> From: Arnd Bergmann >> >> When building with CONFIG_LD_DEAD_CODE_DATA_ELIMINATION, >> I sometimes see an assertion >> >> ld.lld: error: Entry trampoline text too big > >Heh, "too big" seems a weird report for having it discarded. :) > >Any idea on this Fangrui? > >( I see this is https://github.com/ClangBuiltLinux/linux/issues/1311 ) This diagnostic is from an ASSERT in arch/arm64/kernel/vmlinux.lds ASSERT((__entry_tramp_text_end - __entry_tramp_text_start) == (1 << 16), "Entry trampoline text too big") In our case (aarch64-linux-gnu-ld or LLD, --gc-sections), all the input sections with this name are discarded, so the output section is either absent (GNU ld) or empty (LLD). KEEP makes the sections GC roots, and it is appropriate to use here. However, I worry that many other KEEP keywords in vmlinux.lds are unnecessary: https://lore.kernel.org/linux-arm-kernel/20210226211323.arkvjnr4hifxapqu@google.com/ git log -S KEEP -- include/asm-generic/vmlinux.lds.h => there is quite a bit unjustified usage. Sure, adding KEEP (GC root) is easy and works around problems, but it not good for CONFIG_LD_DEAD_CODE_DATA_ELIMINATION. Reviewed-by: Fangrui Song > >> >> This happens when any reference to the trampoline is discarded at link >> time. Marking the section as KEEP() avoids the assertion, but I have >> not figured out whether this is the correct solution for the underlying >> problem. >> >> Signed-off-by: Arnd Bergmann > >As a work-around, it seems fine to me. > >Reviewed-by: Kees Cook > >-Kees > >> --- >> arch/arm64/kernel/vmlinux.lds.S | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S >> index 926cdb597a45..c5ee9d5842db 100644 >> --- a/arch/arm64/kernel/vmlinux.lds.S >> +++ b/arch/arm64/kernel/vmlinux.lds.S >> @@ -96,7 +96,7 @@ jiffies = jiffies_64; >> #define TRAMP_TEXT \ >> . = ALIGN(PAGE_SIZE); \ >> __entry_tramp_text_start = .; \ >> - *(.entry.tramp.text) \ >> + KEEP(*(.entry.tramp.text)) \ >> . = ALIGN(PAGE_SIZE); \ >> __entry_tramp_text_end = .; >> #else >> -- >> 2.29.2 >> > >-- >Kees Cook _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel