[compiler-rt] 4a2da7e - Revert "ASan: move allocator base to avoid conflict with high-entropy ASLR for x86-64 Linux"

[Hans Wennborg via llvm-commits]

Author: Hans Wennborg
Date: 2023-04-13T09:53:06+02:00
New Revision: 4a2da7e8a91bd381ee38fbeb6055e7d97453a789

URL: https://github.com/llvm/llvm-project/commit/4a2da7e8a91bd381ee38fbeb6055e7d97453a789
DIFF: https://github.com/llvm/llvm-project/commit/4a2da7e8a91bd381ee38fbeb6055e7d97453a789.diff

LOG: Revert "ASan: move allocator base to avoid conflict with high-entropy ASLR for x86-64 Linux"

This broke lit tests on Mac, see comment on the code review.

> 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/D147984

This reverts commit 6f42b97a29a5872c115029c615f55f33419a4c1f.

Added: 
    

Modified: 
    compiler-rt/lib/asan/asan_allocator.h

Removed: 
    


################################################################################
diff  --git a/compiler-rt/lib/asan/asan_allocator.h b/compiler-rt/lib/asan/asan_allocator.h
index 05dcd2d6f541c..0b4dbf03bb9d5 100644
--- a/compiler-rt/lib/asan/asan_allocator.h
+++ b/compiler-rt/lib/asan/asan_allocator.h
@@ -144,7 +144,7 @@ const uptr kAllocatorSpace = ~(uptr)0;
 const uptr kAllocatorSize  =  0x8000000000ULL;  // 500G
 typedef DefaultSizeClassMap SizeClassMap;
 # else
-const uptr kAllocatorSpace = 0x500000000000ULL;
+const uptr kAllocatorSpace = 0x600000000000ULL;
 const uptr kAllocatorSize  =  0x40000000000ULL;  // 4T.
 typedef DefaultSizeClassMap SizeClassMap;
 # endif