From mboxrd@z Thu Jan 1 00:00:00 1970 From: Catalin Marinas Subject: Re: [PATCH v10 00/13] arm64: Branch Target Identification support Date: Mon, 23 Mar 2020 12:21:44 +0000 Message-ID: <20200323122143.GB4892@mbp> References: <20200316165055.31179-1-broonie@kernel.org> <20200320173945.GC27072@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20200320173945.GC27072@arm.com> Sender: linux-kernel-owner@vger.kernel.org To: Szabolcs Nagy Cc: Mark Brown , Will Deacon , Alexander Viro , Paul Elliott , Peter Zijlstra , Yu-cheng Yu , Amit Kachhap , Vincenzo Frascino , Marc Zyngier , Eugene Syromiatnikov , "H . J . Lu " , Andrew Jones , Kees Cook , Arnd Bergmann , Jann Horn , Richard Henderson , Kristina =?utf-8?Q?Mart=C5=A1enko?= , Thomas Gleixner , Florian Weimer , Sudakshina Das List-Id: linux-arch.vger.kernel.org On Fri, Mar 20, 2020 at 05:39:46PM +0000, Szabolcs Nagy wrote: > The 03/16/2020 16:50, Mark Brown wrote: > > This patch series implements support for ARMv8.5-A Branch Target > > Identification (BTI), which is a control flow integrity protection > > feature introduced as part of the ARMv8.5-A extensions. > > i was playing with this and it seems the kernel does not add > PROT_BTI to non-static executables (i.e. there is an interpreter). > > i thought any elf that the kernel maps would get PROT_BTI from the > kernel. (i want to remove the mprotect in glibc when not necessary) I haven't followed the early discussions but I think this makes sense. > i tested by linking a hello world exe with -Wl,-z,force-bti (and > verified that the property note is there) and expected it to crash > (with SIGILL) when the dynamic linker jumps to _start in the exe, > but it executed without errors (if i do the mprotect in glibc then > i get SIGILL as expected). > > is this deliberate? does the kernel map static exe and dynamic > linked exe differently? I think the logic is in patch 5: +int arch_elf_adjust_prot(int prot, const struct arch_elf_state *state, + bool has_interp, bool is_interp) +{ + if (is_interp != has_interp) + return prot; + + if (!(state->flags & ARM64_ELF_BTI)) + return prot; + + if (prot & PROT_EXEC) + prot |= PROT_BTI; + + return prot; +} At a quick look, for dynamic binaries we have has_interp == true and is_interp == false. I don't know why but, either way, the above code needs a comment with some justification. -- Catalin From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from foss.arm.com ([217.140.110.172]:48184 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727531AbgCWMVu (ORCPT ); Mon, 23 Mar 2020 08:21:50 -0400 Date: Mon, 23 Mar 2020 12:21:44 +0000 From: Catalin Marinas Subject: Re: [PATCH v10 00/13] arm64: Branch Target Identification support Message-ID: <20200323122143.GB4892@mbp> References: <20200316165055.31179-1-broonie@kernel.org> <20200320173945.GC27072@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200320173945.GC27072@arm.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Szabolcs Nagy Cc: Mark Brown , Will Deacon , Alexander Viro , Paul Elliott , Peter Zijlstra , Yu-cheng Yu , Amit Kachhap , Vincenzo Frascino , Marc Zyngier , Eugene Syromiatnikov , "H . J . Lu " , Andrew Jones , Kees Cook , Arnd Bergmann , Jann Horn , Richard Henderson , Kristina =?utf-8?Q?Mart=C5=A1enko?= , Thomas Gleixner , Florian Weimer , Sudakshina Das , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-fsdevel@vger.kernel.org, nd@arm.com Message-ID: <20200323122144.Ca-JJMsI1knap15yh0u624L1JhSloKpoTCESVVmexhs@z> On Fri, Mar 20, 2020 at 05:39:46PM +0000, Szabolcs Nagy wrote: > The 03/16/2020 16:50, Mark Brown wrote: > > This patch series implements support for ARMv8.5-A Branch Target > > Identification (BTI), which is a control flow integrity protection > > feature introduced as part of the ARMv8.5-A extensions. > > i was playing with this and it seems the kernel does not add > PROT_BTI to non-static executables (i.e. there is an interpreter). > > i thought any elf that the kernel maps would get PROT_BTI from the > kernel. (i want to remove the mprotect in glibc when not necessary) I haven't followed the early discussions but I think this makes sense. > i tested by linking a hello world exe with -Wl,-z,force-bti (and > verified that the property note is there) and expected it to crash > (with SIGILL) when the dynamic linker jumps to _start in the exe, > but it executed without errors (if i do the mprotect in glibc then > i get SIGILL as expected). > > is this deliberate? does the kernel map static exe and dynamic > linked exe differently? I think the logic is in patch 5: +int arch_elf_adjust_prot(int prot, const struct arch_elf_state *state, + bool has_interp, bool is_interp) +{ + if (is_interp != has_interp) + return prot; + + if (!(state->flags & ARM64_ELF_BTI)) + return prot; + + if (prot & PROT_EXEC) + prot |= PROT_BTI; + + return prot; +} At a quick look, for dynamic binaries we have has_interp == true and is_interp == false. I don't know why but, either way, the above code needs a comment with some justification. -- Catalin