| From 8defb3367fcd19d1af64c07792aade0747b54e0f Mon Sep 17 00:00:00 2001 |
| From: Andrey Ryabinin <a.ryabinin@samsung.com> |
| Date: Fri, 20 Mar 2015 15:42:27 +0100 |
| Subject: ARM: 8320/1: fix integer overflow in ELF_ET_DYN_BASE |
| |
| From: Andrey Ryabinin <a.ryabinin@samsung.com> |
| |
| 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 <a.ryabinin@samsung.com> |
| Reported-by: Maria Guseva <m.guseva@samsung.com> |
| Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| arch/arm/include/asm/elf.h | 2 +- |
| 1 file changed, 1 insertion(+), 1 deletion(-) |
| |
| --- a/arch/arm/include/asm/elf.h |
| +++ b/arch/arm/include/asm/elf.h |
| @@ -115,7 +115,7 @@ int dump_task_regs(struct task_struct *t |
| 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 |
