On 23 June 2017 at 14:02, Kees Cook <keescook@xxxxxxxxxxxx> wrote: > On Fri, Jun 23, 2017 at 6:52 AM, Kees Cook <keescook@xxxxxxxxxxxx> wrote: >> On Thu, Jun 22, 2017 at 11:57 PM, Ard Biesheuvel >> <ard.biesheuvel@xxxxxxxxxx> wrote: >>> Hi Kees, >>> >>> On 22 June 2017 at 18:06, Kees Cook <keescook@xxxxxxxxxxxx> wrote: >>>> Now that explicitly executed loaders are loaded in the mmap region, >>>> position PIE binaries lower in the address space to avoid possible >>>> collisions with mmap or stack regions. For 64-bit, align to 4GB to >>>> allow runtimes to use the entire 32-bit address space for 32-bit >>>> pointers. >>>> >>>> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> >>>> --- >>>> arch/arm64/include/asm/elf.h | 13 ++++++------- >>>> 1 file changed, 6 insertions(+), 7 deletions(-) >>>> >>>> diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h >>>> index 5d1700425efe..f742af8f7c42 100644 >>>> --- a/arch/arm64/include/asm/elf.h >>>> +++ b/arch/arm64/include/asm/elf.h >>>> @@ -113,12 +113,13 @@ >>>> #define ELF_EXEC_PAGESIZE PAGE_SIZE >>>> >>>> /* >>>> - * This is the location that an ET_DYN program is loaded if exec'ed. Typical >>>> - * use of this is to invoke "./ld.so someprog" to test out a new version of >>>> - * 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. >>>> + * 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 >>>> + * space open for things that want to use the area for 32-bit pointers. >>>> */ >>>> -#define ELF_ET_DYN_BASE (2 * TASK_SIZE_64 / 3) >>>> +#define ELF_ET_DYN_BASE (test_thread_flag(TIF_32BIT) ? \ >>>> + 0x000400000UL : \ >>>> + 0x100000000UL) >>>> >>> >>> Why are you merging this with the COMPAT definition? >> >> It seemed like the right thing to do since a single definition could >> handle both cases. Is there something I'm overlooking in the arm64 >> case? > > And like 5 minutes later there was a loud head-slapping noise in my > office. Durr, yeah, arm64 doesn't have to deal with a "native 32-bit" > mode, so the merge isn't needed. Yes yes, I will split it back up and > drop the thread flag test. > Oh, is that what I heard?
