Date: Thu, 24 May 2012 00:57:52 -0400 From: Rich Felker <dalias@...ifal.cx> To: musl@...ts.openwall.com Subject: Static PIE! (experimental) I've got very experimental static-linked PIE support working, using the attached files. This isn't ready to go in (in fact, part of it belongs in binutils' ldscripts, not musl), but it's a very cool proof of concept. Some caveats: - ALL object files, including those in static libs (that means libc too!) must be built with -fPIE or -fPIC. So to use this, you really need to commit to building your whole system this way. - No error checking is done for invalid binaries; they'll likely crash horribly. You can use readelf -a to check that the only relocations are RELATIVE. If you see any other types of reloc, the binary is broken (miscompiled or mislinked). - Textrels are not supported. They would be very difficult to support on hardened systems that don't allow RWX pages, since the binary would be self-modifying while running (and thus switching temporarily to RW- and later to R-X would not suffice). - The provided linker script is for i386, but it's just a simple change to the original file (sending .interp section to /DISCARD/) and you can make the same change for any arch. Likewise, Zcrt1.s is for i386, but it's trivially generated from Scrt1.s by adding a call to __static_pie_reloc. Command to use to link: gcc -static -pie -fPIE -nostartfiles Zcrt1.s Zcrt2.c \ /usr/lib/crt[in].o -Wl,-T,elf_i386.xd "$@" Of course you can pre-compile/assemble Zcrt1.o and Zcrt2.o if you like. The reason they're split into 2 files is that the first is startup asm (arch-specific) and the latter is written in C for convenience (and arch-independence). To get this to production stage... 1. The linker scripts need to be incorporated into binutils. 2. The gcc specfile needs to be edited to use alternate startfiles when both -static and -pie are specified. 3. The new crt files need to be added to musl. By the way, there's nothing musl-specific about any of this. If anybody wants to build a static glibc with -fPIE and patch the call to __static_pie_reloc into its startfiles, it should work too.. Same goes for uClibc. Rich View attachment "Zcrt1.s" of type "text/plain" (441 bytes) View attachment "Zcrt2.c" of type "text/plain" (1056 bytes) View attachment "elf_i386.xd" of type "text/plain" (7095 bytes)
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