Re: ldd not working on ET_EXEC executables

[Laine Gholson <laine.gholson@gmail.com>]

You mean RANDMMAP? PaX's RANDMMAP feature ignoring the address your requesting it (without MAP_FIXED) is perfectly valid, to quote POSIX:
"When MAP_FIXED is not set, the implementation uses addr in an implementation-defined manner to arrive at pa."
mmap2(0x10000, 73728, PROT_READ|PROT_EXEC, MAP_PRIVATE, 3, 0) = 0x1234abcd
You're not passing MAP_FIXED to mmap() but are expecting the kernel to still use the address you're giving it, which is wrong.

(as a side note, glibc works and it uses MAP_FIXED)

Thanks,

Laine Gholson

On 12/05/16 20:33, Rich Felker wrote:
> On Mon, Dec 05, 2016 at 07:39:32PM -0600, Laine Gholson wrote:
>> Hello,
>>
>> I am running musl on a ARM platform, and ldd won't work on a executable with the ET_EXEC type.
>>
>> running GNU ld 2.25.1, gcc 6.2.0, and musl 1.1.15-git-71-g54991729
>>
>>  $ gcc -fPIE -pie test.c -o test-pie
>>  $ ldd test-pie
>> <no error>
>>  $ gcc -fno-PIE -no-pie test.c -o test-nopie
>>  $ ldd test-nopie
>> ldd: test-nopie: Not a valid dynamic program
>>  $ elfedit --output-type DYN test-nopie
>>  $ ldd test-nopie
>> <no error>
>>
>> Any idea why ldd says executables with the ET_EXEC type aren't valid?
>
> strace it; I suspect you'll find that mmap is not honoring the
> requested address. This is a bug introduced intentionally by grsec/pax
> and perhaps other hardened kernels.
>
> Rich
>