On Sat, 17 Feb 2024 at 07:50, Kees Cook <keesc...@chromium.org> wrote: > > *extreme thread[1] necromancy* > > 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). > > I happened to be looking at this again today, and wondered where things > stood. It seems like ASan's mappings are documented here: > https://github.com/google/sanitizers/wiki/AddressSanitizerAlgorithm#64-bit > > This implies that it would be safe to move the ELF_ET_DYN_BASE from > 0x555555554000 down to 0x200000000000, since the shadow map ends at > 0x10007fff7fff. (Well, anything above there would work, I was just > picking a "round" number above it. We could just as well use > 0x100080000000, I think.) > > Is this correct? I'd like to open up some more room between mmap and > stack...
Note that there is also TSAN and MSAN with their own mappings. These are also different per-arch, e.g. TSAN/Linux/x86_64: https://github.com/llvm/llvm-project/blob/d2a26a7bd5fc7cc5752337b7f4f999642feb37dc/compiler-rt/lib/tsan/rtl/tsan_platform.h#L48-L58 Search "linux/" in that file for other arches, e.g.: https://github.com/llvm/llvm-project/blob/d2a26a7bd5fc7cc5752337b7f4f999642feb37dc/compiler-rt/lib/tsan/rtl/tsan_platform.h#L156-L165 https://github.com/llvm/llvm-project/blob/d2a26a7bd5fc7cc5752337b7f4f999642feb37dc/compiler-rt/lib/tsan/rtl/tsan_platform.h#L187-L196 https://github.com/llvm/llvm-project/blob/d2a26a7bd5fc7cc5752337b7f4f999642feb37dc/compiler-rt/lib/tsan/rtl/tsan_platform.h#L218-L227 https://github.com/llvm/llvm-project/blob/d2a26a7bd5fc7cc5752337b7f4f999642feb37dc/compiler-rt/lib/tsan/rtl/tsan_platform.h#L252-L263 And MSAN mappings: https://github.com/llvm/llvm-project/blob/d2a26a7bd5fc7cc5752337b7f4f999642feb37dc/compiler-rt/lib/msan/msan.h#L44-L61 > Thanks! > > -Kees > > [1] https://lore.kernel.org/lkml/20170807201542.GA21271@beast/ > > > > > 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 <k...@google.com> > > Cc: sta...@vger.kernel.org > > Signed-off-by: Kees Cook <keesc...@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__ > > > > diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h > > index 1c18d83d3f09..9aeb91935ce0 100644 > > --- a/arch/x86/include/asm/elf.h > > +++ b/arch/x86/include/asm/elf.h > > @@ -247,11 +247,11 @@ extern int force_personality32; > > > > /* > > * 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 (mmap_is_ia32() ? 0x000400000UL : \ > > - 0x100000000UL) > > + (TASK_SIZE / 3 * 2)) > > > > /* This yields a mask that user programs can use to figure out what > > instruction set this CPU supports. This could be done in user space, > > -- > > 2.7.4 > > > > > > -- > > Kees Cook > > Pixel Security > > -- > Kees Cook -- You received this message because you are subscribed to the Google Groups "address-sanitizer" group. To unsubscribe from this group and stop receiving emails from it, send an email to address-sanitizer+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/address-sanitizer/CACT4Y%2BZnNdb1z7oSq0zb3XHFTcdEwSMFvcvLJxm1VrgnpaohMw%40mail.gmail.com.