From fb77ca05ffb4f8e666878f2f6718a9fb4d686839 Mon Sep 17 00:00:00 2001 From: Thurston Dang Date: Thu, 13 Apr 2023 23:55:01 +0000 Subject: [PATCH] Re-land 'ASan: move allocator base to avoid conflict with high-entropy ASLR for x86-64 Linux' D147984 was reverted because it broke lit tests on Mac. This revision is based on D147984 but maintains the old behavior for Apple. Note that, per the follow-up discussion with MaskRay in D147984, this patch excludes Apple but includes other platforms (e.g., aarch64, MIPS64) and OSes (e.g., FreeBSD, S390X), not just x86-64 Linux. Original commit message from D147984: Users have discovered [*] that when CONFIG_ARCH_MMAP_RND_BITS == 32, it will frequently conflict with ASan's allocator on x86-64 Linux, because the PIE program segment base address of 0x555555555554 plus an ASLR shift of up to ((2**32) * 4K == 0x100000000000) will sometimes exceed ASan's hardcoded base address of 0x600000000000. We fix this by simply moving the allocator base to 0x500000000000, which is below the PIE program segment base address. This is cleaner than trying to move it to another location that is sandwiched between the PIE program and library segments, because if either of those grow too large, it will collide with the allocator region. Note that we will never need to change this base address again (unless we want to increase the size of the allocator), because ASLR cannot be set above 32-bits for x86-64 Linux (the PIE program segment and library segments would collide with each other; see also ARCH_MMAP_RND_BITS_MAX in https://github.com/torvalds/linux/blob/master/arch/x86/Kconfig). [*] see https://b.corp.google.com/issues/276925478 and https://groups.google.com/a/google.com/g/chrome-os-gardeners/c/BbfzCP3dEeo/m/h3C_vVUxCQAJ Differential Revision: https://reviews.llvm.org/D148280 --- compiler-rt/lib/asan/asan_allocator.h | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/compiler-rt/lib/asan/asan_allocator.h b/compiler-rt/lib/asan/asan_allocator.h index 0b4dbf03bb9d5..6a12a6c602528 100644 --- a/compiler-rt/lib/asan/asan_allocator.h +++ b/compiler-rt/lib/asan/asan_allocator.h @@ -143,11 +143,15 @@ typedef DefaultSizeClassMap SizeClassMap; const uptr kAllocatorSpace = ~(uptr)0; const uptr kAllocatorSize = 0x8000000000ULL; // 500G typedef DefaultSizeClassMap SizeClassMap; -# else +# elif SANITIZER_APPLE const uptr kAllocatorSpace = 0x600000000000ULL; const uptr kAllocatorSize = 0x40000000000ULL; // 4T. typedef DefaultSizeClassMap SizeClassMap; -# endif +# else +const uptr kAllocatorSpace = 0x500000000000ULL; +const uptr kAllocatorSize = 0x40000000000ULL; // 4T. +typedef DefaultSizeClassMap SizeClassMap; +# endif template struct AP64 { // Allocator64 parameters. Deliberately using a short name. static const uptr kSpaceBeg = kAllocatorSpace;