Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753864AbaJGNoi (ORCPT ); Tue, 7 Oct 2014 09:44:38 -0400 Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:56316 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751266AbaJGNoh (ORCPT ); Tue, 7 Oct 2014 09:44:37 -0400 Date: Tue, 7 Oct 2014 14:43:50 +0100 From: Mark Rutland To: Arun Chandran Cc: Catalin Marinas , Will Deacon , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Anton Blanchard , Benjamin Herrenschmidt , Paul Mackerras , Heiko Carstens , Martin Schwidefsky Subject: Re: [PATCH v1] Arm64: ASLR: fix text randomization Message-ID: <20141007134349.GR24725@leverpostej> References: <1412685628-27178-1-git-send-email-achandran@mvista.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1412685628-27178-1-git-send-email-achandran@mvista.com> Thread-Topic: [PATCH v1] Arm64: ASLR: fix text randomization Accept-Language: en-GB, en-US Content-Language: en-US acceptlanguage: en-GB, en-US User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 07, 2014 at 01:40:28PM +0100, Arun Chandran wrote: > This is due to incorrect definition of ELF_ET_DYN_BASE. It > introduces randomization for text even if user does a "echo 0 > > /proc/sys/kernel/randomize_va_space" Interesting. It looks like this was a copy of what powerpc and s390 do (authors Cc'd), and the generic support came later. powerpc gained support in 501cb16d3cfdcca9 (powerpc: Randomise PIEs), but the generic support was enabled later in e39f560239984c30 (fs: binfmt_elf: create Kconfig variable for PIE randomization). The policy of disabling PIE randomization was added in a3defbe5c337dbc6 (binfmt_elf: fix PIE execution with randomization disabled), after the powerpc implementation, but before the x86 implementation was made generic. I wasn't able to spot where the randomness came from in the ARCH_BINFMT_ELF_RANDOMIZE_PIE case, so it's not clear to me if the generic implementation behaves identically other than disabling randomization when told to via proc. Assuming it behaves similarly enough, it looks like arm64, powerpc, and s390 should all be moved over. > > Signed-off-by: Arun Chandran > --- > This can be tested using the code below > > #include > > int main(int argc, char *argv) > { > printf("main = %p\n", main); > return 0; > } > > * compile it possition independently > aarch64-linux-gnu-gcc -fPIE -pie aslr.c -o aslr > > * run it on the target > > # ./aslr > main = 0x7f87138950 > # ./aslr > main = 0x7f94a10950 > # ./aslr > main = 0x7f94fee950 > # ./aslr text > main = 0x7f8cb72950 > > # echo 0 > /proc/sys/kernel/randomize_va_space > # ./aslr text > main = 0x5555555950 > # ./aslr > main = 0x5555555950 > # ./aslr > main = 0x5555555950 > # ./aslr > main = 0x5555555950 It would be worth pointing out that this is after your patch is applied. Before your patch I get randomized VAs even after writing 0 to randomize_va_spave. > --- > arch/arm64/Kconfig | 1 + > arch/arm64/include/asm/elf.h | 4 ++-- > 2 files changed, 3 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index fd4e81a..a2eefc9 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -1,5 +1,6 @@ > config ARM64 > def_bool y > + select ARCH_BINFMT_ELF_RANDOMIZE_PIE > select ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE > select ARCH_HAS_SG_CHAIN > select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST > diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h > index 01d3aab..1f65be3 100644 > --- a/arch/arm64/include/asm/elf.h > +++ b/arch/arm64/include/asm/elf.h > @@ -126,7 +126,7 @@ typedef struct user_fpsimd_state elf_fpregset_t; > * that it will "exec", and that there is sufficient room for the brk. > */ > extern unsigned long randomize_et_dyn(unsigned long base); > -#define ELF_ET_DYN_BASE (randomize_et_dyn(2 * TASK_SIZE_64 / 3)) > +#define ELF_ET_DYN_BASE (2 * TASK_SIZE_64 / 3) > > /* > * When the program starts, a1 contains a pointer to a function to be > @@ -169,7 +169,7 @@ extern unsigned long arch_randomize_brk(struct mm_struct *mm); > #define COMPAT_ELF_PLATFORM ("v8l") > #endif > > -#define COMPAT_ELF_ET_DYN_BASE (randomize_et_dyn(2 * TASK_SIZE_32 / 3)) > +#define COMPAT_ELF_ET_DYN_BASE (2 * TASK_SIZE_32 / 3) > > /* AArch32 registers. */ > #define COMPAT_ELF_NGREG 18 > -- > 1.7.9.5 Given randomize_et_dyn is no longer used after this patch, I think it should be dropped from arch/arm64/kernel/process.c. Thanks, Mark. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/