Messages in this thread | | | From | Kees Cook <> | Date | Tue, 8 Aug 2017 19:00:32 -0700 | Subject | Re: [PATCH] mm: Revert x86_64 and arm64 ELF_ET_DYN_BASE base |
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On Tue, Aug 8, 2017 at 2:34 AM, Will Deacon <will.deacon@arm.com> wrote: > 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@google.com> >> Cc: stable@vger.kernel.org >> Signed-off-by: Kees Cook <keescook@chromium.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@arm.com> > > I assume this is going via akpm like the original commit?
That's my expectation, yup. Thanks for the Ack!
-Kees
-- Kees Cook Pixel Security
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