From 0e75ad3733bf2086beb13b493c73f168a691e6e4 Mon Sep 17 00:00:00 2001 From: Andrey Ryabinin Date: Fri, 20 Mar 2015 15:42:27 +0100 Subject: [PATCH] ARM: 8320/1: fix integer overflow in ELF_ET_DYN_BASE commit 8defb3367fcd19d1af64c07792aade0747b54e0f upstream. Usually ELF_ET_DYN_BASE is 2/3 of TASK_SIZE. With 3G/1G user/kernel split this is not so, because 2*TASK_SIZE overflows 32 bits, so the actual value of ELF_ET_DYN_BASE is: (2 * TASK_SIZE / 3) = 0x2a000000 When ASLR is disabled PIE binaries will load at ELF_ET_DYN_BASE address. On 32bit platforms AddressSanitzer uses addresses [0x20000000 - 0x40000000] for shadow memory [1]. So ASan doesn't work for PIE binaries when ASLR disabled as it fails to map shadow memory. Also after Kees's 'split ET_DYN ASLR from mmap ASLR' patchset PIE binaries has a high chance of loading somewhere in between [0x2a000000 - 0x40000000] even if ASLR enabled. This makes ASan with PIE absolutely incompatible. Fix overflow by dividing TASK_SIZE prior to multiplying. After this patch ELF_ET_DYN_BASE equals to (for CONFIG_VMSPLIT_3G=y): (TASK_SIZE / 3 * 2) = 0x7f555554 [1] https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerAlgorithm#Mapping Signed-off-by: Andrey Ryabinin Reported-by: Maria Guseva Signed-off-by: Russell King Signed-off-by: Ben Hutchings --- arch/arm/include/asm/elf.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/arm/include/asm/elf.h b/arch/arm/include/asm/elf.h index 0e9ce8d9686e..a4b118607501 100644 --- a/arch/arm/include/asm/elf.h +++ b/arch/arm/include/asm/elf.h @@ -116,7 +116,7 @@ int dump_task_regs(struct task_struct *t, elf_gregset_t *elfregs); the loader. We need to make sure that it is out of the way of the program that it will "exec", and that there is sufficient room for the brk. */ -#define ELF_ET_DYN_BASE (2 * TASK_SIZE / 3) +#define ELF_ET_DYN_BASE (TASK_SIZE / 3 * 2) /* When the program starts, a1 contains a pointer to a function to be registered with atexit, as per the SVR4 ABI. A value of 0 means we -- 2.39.2