Date: Thu, 8 Dec 2016 17:41:21 -0500 From: Rich Felker <dalias@...c.org> To: musl@...ts.openwall.com Subject: Re: ldd not working on ET_EXEC executables On Thu, Dec 08, 2016 at 04:30:42PM -0600, Laine Gholson wrote: > 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 It's _valid_, but it's a bad implementation choice; it makes it impossible to request a particular range, which is necessary for ldso/ldd to load non-PIE programs. > 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) This is invalid, and a bug in glibc, as there's no way to know that you're not mapping over something that's already there (perhaps even the function that's calling mmap). You can only use MAP_FIXED to map over top of an existing mapping you already know about and intend to replace (same with dup2 and file descriptors), not an arbitrary address range. Rich > 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 > >
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