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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 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 09DC4C28CBC for ; Wed, 6 May 2020 12:03:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E17A5206DD for ; Wed, 6 May 2020 12:03:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727935AbgEFMDX (ORCPT ); Wed, 6 May 2020 08:03:23 -0400 Received: from foss.arm.com ([217.140.110.172]:34950 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727805AbgEFMDW (ORCPT ); Wed, 6 May 2020 08:03:22 -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 DAC661FB; Wed, 6 May 2020 05:03:21 -0700 (PDT) Received: from [10.57.31.214] (unknown [10.57.31.214]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 446353F71F; Wed, 6 May 2020 05:03:19 -0700 (PDT) From: Amit Kachhap Subject: Re: [PATCH v2 1/2] arm64/crash_core: Export KERNELPACMASK in vmcoreinfo To: Will Deacon Cc: linux-arm-kernel@lists.infradead.org, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, Catalin Marinas , Bhupesh Sharma , Vincenzo Frascino , James Morse , Mark Rutland References: <1587968702-19996-1-git-send-email-amit.kachhap@arm.com> <20200504171741.GD1833@willie-the-truck> Message-ID: Date: Wed, 6 May 2020 17:32:56 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20200504171741.GD1833@willie-the-truck> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Will, On 5/4/20 10:47 PM, Will Deacon wrote: > On Mon, Apr 27, 2020 at 11:55:01AM +0530, Amit Daniel Kachhap wrote: >> Recently arm64 linux kernel added support for Armv8.3-A Pointer >> Authentication feature. If this feature is enabled in the kernel and the >> hardware supports address authentication then the return addresses are >> signed and stored in the stack to prevent ROP kind of attack. Kdump tool >> will now dump the kernel with signed lr values in the stack. >> >> Any user analysis tool for this kernel dump may need the kernel pac mask >> information in vmcoreinfo to generate the correct return address for >> stacktrace purpose as well as to resolve the symbol name. >> >> This patch is similar to commit ec6e822d1a22d0eef ("arm64: expose user PAC >> bit positions via ptrace") which exposes pac mask information via ptrace >> interfaces. >> >> Cc: Catalin Marinas >> Cc: Will Deacon >> Cc: Mark Rutland >> Signed-off-by: Amit Daniel Kachhap >> --- >> Changes since v1: >> * Rebased to kernel 5.7-rc3. >> * commit log change. >> >> An implementation of this new KERNELPACMASK vmcoreinfo field used by crash >> tool can be found here[1]. This change is accepted by crash utility >> maintainer [2]. >> >> [1]: https://www.redhat.com/archives/crash-utility/2020-April/msg00095.html >> [2]: https://www.redhat.com/archives/crash-utility/2020-April/msg00099.html >> >> arch/arm64/include/asm/compiler.h | 3 +++ >> arch/arm64/kernel/crash_core.c | 4 ++++ >> 2 files changed, 7 insertions(+) >> >> diff --git a/arch/arm64/include/asm/compiler.h b/arch/arm64/include/asm/compiler.h >> index eece20d..32d5900 100644 >> --- a/arch/arm64/include/asm/compiler.h >> +++ b/arch/arm64/include/asm/compiler.h >> @@ -19,6 +19,9 @@ >> #define __builtin_return_address(val) \ >> (void *)(ptrauth_clear_pac((unsigned long)__builtin_return_address(val))) >> >> +#else /* !CONFIG_ARM64_PTR_AUTH */ >> +#define ptrauth_user_pac_mask() 0ULL >> +#define ptrauth_kernel_pac_mask() 0ULL > > This doesn't look quite right to me, since you still have to take into > account the case where CONFIG_ARM64_PTR_AUTH=y but the feature is not > available at runtime: Yes agree with you here. However the config gaurd is saving some extra computation for __builtin_return_address. There are some compiler support being added in __builtin_extract_return_address to mask the PAC. Hopefully that will improve this code. In the meantime let it be like this. I can remove this else case and as other users of ptrauth_{kernel,user}_pac_mask(ptrace.c) protect it with a config gaurd there. > >> @@ -16,4 +17,7 @@ void arch_crash_save_vmcoreinfo(void) >> vmcoreinfo_append_str("NUMBER(PHYS_OFFSET)=0x%llx\n", >> PHYS_OFFSET); >> vmcoreinfo_append_str("KERNELOFFSET=%lx\n", kaslr_offset()); >> + vmcoreinfo_append_str("NUMBER(KERNELPACMASK)=0x%llx\n", >> + system_supports_address_auth() ? >> + ptrauth_kernel_pac_mask() : 0); > > In which case, would it make more sense to define > ptrauth_{kernel,user}_pac_mask() unconditionally? In fact, I'd probably > just remove the guards completely from asm/compiler.h because I think > they're misleading. As answered above. Let me know your opinion. Although I don't have strong reservation in keeping the config gaurd. Thanks, Amit Daniel > > Will > > --->8 > > diff --git a/arch/arm64/include/asm/compiler.h b/arch/arm64/include/asm/compiler.h > index eece20d2c55f..51a7ce87cdfe 100644 > --- a/arch/arm64/include/asm/compiler.h > +++ b/arch/arm64/include/asm/compiler.h > @@ -2,8 +2,6 @@ > #ifndef __ASM_COMPILER_H > #define __ASM_COMPILER_H > > -#if defined(CONFIG_ARM64_PTR_AUTH) > - > /* > * The EL0/EL1 pointer bits used by a pointer authentication code. > * This is dependent on TBI0/TBI1 being enabled, or bits 63:56 would also apply. > @@ -19,6 +17,4 @@ > #define __builtin_return_address(val) \ > (void *)(ptrauth_clear_pac((unsigned long)__builtin_return_address(val))) > > -#endif /* CONFIG_ARM64_PTR_AUTH */ > - > #endif /* __ASM_COMPILER_H */ >