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Date: Tue, 8 Aug 2017 10:34:50 +0100 From: Will Deacon <will.deacon@....com> To: Kees Cook <keescook@...omium.org> Cc: Andrew Morton <akpm@...ux-foundation.org>, Kostya Serebryany <kcc@...gle.com>, Evgeniy Stepanov <eugenis@...gle.com>, Daniel Micay <danielmicay@...il.com>, Dmitry Vyukov <dvyukov@...gle.com>, Catalin Marinas <catalin.marinas@....com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org, Pratyush Anand <panand@...hat.com>, Dong Bo <dongbo4@...wei.com>, Dmitry Safonov <dsafonov@...tuozzo.com>, Rik van Riel <riel@...hat.com>, Andy Lutomirski <luto@...capital.net>, Grzegorz Andrejczuk <grzegorz.andrejczuk@...el.com>, linux-arm-kernel@...ts.infradead.org, Reid Kleckner <rnk@...gle.com>, Peter Collingbourne <pcc@...gle.com>, linux-kernel@...r.kernel.org Subject: Re: [PATCH] mm: Revert x86_64 and arm64 ELF_ET_DYN_BASE base On Mon, Aug 07, 2017 at 01:15:42PM -0700, Kees Cook wrote: > Moving the x86_64 and arm64 PIE base from 0x555555554000 to 0x000100000000 > broke AddressSanitizer. This is a partial revert of: > > commit eab09532d400 ("binfmt_elf: use ELF_ET_DYN_BASE only for PIE") > commit 02445990a96e ("arm64: move ELF_ET_DYN_BASE to 4GB / 4MB") > > The AddressSanitizer tool has hard-coded expectations about where > executable mappings are loaded. The motivation for changing the PIE > base in the above commits was to avoid the Stack-Clash CVEs that > allowed executable mappings to get too close to heap and stack. This > was mainly a problem on 32-bit, but the 64-bit bases were moved too, > in an effort to proactively protect those systems (proofs of concept > do exist that show 64-bit collisions, but other recent changes to fix > stack accounting and setuid behaviors will minimize the impact). > > The new 32-bit PIE base is fine for ASan (since it matches the ET_EXEC > base), so only the 64-bit PIE base needs to be reverted to let x86 and > arm64 ASan binaries run again. Future changes to the 64-bit PIE base on > these architectures can be made optional once a more dynamic method for > dealing with AddressSanitizer is found. (e.g. always loading PIE into > the mmap region for marked binaries.) > > Reported-by: Kostya Serebryany <kcc@...gle.com> > Cc: stable@...r.kernel.org > Signed-off-by: Kees Cook <keescook@...omium.org> > --- > arch/arm64/include/asm/elf.h | 4 ++-- > arch/x86/include/asm/elf.h | 4 ++-- > 2 files changed, 4 insertions(+), 4 deletions(-) > > diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h > index acae781f7359..3288c2b36731 100644 > --- a/arch/arm64/include/asm/elf.h > +++ b/arch/arm64/include/asm/elf.h > @@ -114,10 +114,10 @@ > > /* > * This is the base location for PIE (ET_DYN with INTERP) loads. On > - * 64-bit, this is raised to 4GB to leave the entire 32-bit address > + * 64-bit, this is above 4GB to leave the entire 32-bit address > * space open for things that want to use the area for 32-bit pointers. > */ > -#define ELF_ET_DYN_BASE 0x100000000UL > +#define ELF_ET_DYN_BASE (2 * TASK_SIZE_64 / 3) > > #ifndef __ASSEMBLY__ Acked-by: Will Deacon <will.deacon@....com> I assume this is going via akpm like the original commit? Will
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