[uclibc-ng-devel] [Patch v4] Static PIE support for i386, x86_64, and arm

Hello, I first want to apologize for so many patch versions. This version of the patch correctly adjusts the offset of the TLS initimage used by __libc_setup_tls when copying. I would love feedback on my modifications to libc-tls.c as I had to use a new global variable defined in reloc_static_pie.c containing the load address. Originally I attempted to copy how glibc pulls the load address from a memory map when initializing the TLS, however I could not find a similar structure available in __libc_setup_tls. I would love to know if there is a better method which I overlooked. From 30b435a0b7a7f2d4323eafea2bcebb087cc62462 Mon Sep 17 00:00:00 2001 From: linted &lt;linted(a)users.noreply.github.com&gt; Date: Sat, 23 Jul 2022 16:25:41 -0400 Subject: [PATCH] Added support for creation of Static Position-Independent Executables (PIE) on i386, x86_64, and arm. This patch adds the generation of rcrt1.o which is used by gcc when compiling with the --static-pie flag. rcrt1.o differs from crt1.o and Scrt1.o in that it the executable has a dynamic section but no relocations have been performed prior to _start being called. crt1.o assumes there to be no dynamic relocations, and Scrt1.o has all relocations performed prior to execution by lsdo. The new reloc_static_pie function handles parsing the dynamic section, and performing the relocations in a architecture agnostic method. It also sets _dl_load_base which is used when initalizing TLS to ensure loading from the proper location. This allows for easier porting of static-pie support to additional architectures as only modifications to crt1.S to find the load address are required. Signed-off-by: linted &lt;linted(a)users.noreply.github.com&gt; --- Makerules | 5 +++ extra/Configs/Config.in | 5 +++ libc/misc/internals/Makefile.in | 1 + libc/misc/internals/reloc_static_pie.c | 47 +++++++++++++++++++++ libc/sysdeps/linux/arm/crt1.S | 19 +++++++++ libc/sysdeps/linux/i386/crt1.S | 20 +++++++++ libc/sysdeps/linux/x86_64/crt1.S | 16 ++++++- libpthread/nptl/sysdeps/generic/Makefile.in | 4 ++ libpthread/nptl/sysdeps/generic/libc-tls.c | 4 ++ 9 files changed, 120 insertions(+), 1 deletion(-) create mode 100644 libc/misc/internals/reloc_static_pie.c diff --git a/Makerules b/Makerules index fd40e6c7b..845d81897 100644 --- a/Makerules +++ b/Makerules @@ -405,8 +405,13 @@ else CRTS=$(top_builddir)lib/$(CRT).o endif +ifeq ($(STATIC_PIE),y) +CRTS+=$(top_builddir)lib/r$(CRT).o +endif + ASFLAGS-$(CRT).o := -DL_$(CRT) ASFLAGS-S$(CRT).o := $(PIEFLAG) -DL_S$(CRT) +ASFLAGS-r$(CRT).o := $(PIEFLAG) -DL_r$(CRT) $(CRTS): $(top_srcdir)libc/sysdeps/linux/$(TARGET_ARCH)/$(CRT).S $(compile.S) $(Q)$(STRIPTOOL) -x -R .note -R .comment $@ diff --git a/extra/Configs/Config.in b/extra/Configs/Config.in index a58ceb265..a49278b30 100644 --- a/extra/Configs/Config.in +++ b/extra/Configs/Config.in @@ -301,6 +301,11 @@ config DOPIC If you wish to build all of uClibc as PIC objects, then answer Y here. If you are unsure, then you should answer N. +config STATIC_PIE + bool "Add support for Static Position Independent Executables (PIE)" + default n + depends on DOPIC && !UCLIBC_FORMAT_FDPIC_ELF && (TARGET_arm || TARGET_i386 || TARGET_x86_64) + config ARCH_HAS_NO_SHARED bool diff --git a/libc/misc/internals/Makefile.in b/libc/misc/internals/Makefile.in index a8e4e36f9..4a6e73d2d 100644 --- a/libc/misc/internals/Makefile.in +++ b/libc/misc/internals/Makefile.in @@ -34,6 +34,7 @@ libc-static-$(UCLIBC_FORMAT_FLAT_SEP_DATA) += \ libc-static-$(UCLIBC_FORMAT_SHARED_FLAT) += \ $(MISC_INTERNALS_OUT)/shared_flat_initfini.o \ $(MISC_INTERNALS_OUT)/shared_flat_add_library.o +libc-static-$(STATIC_PIE) += $(MISC_INTERNALS_OUT)/reloc_static_pie.o libc-shared-$(UCLIBC_FORMAT_SHARED_FLAT) += \ $(MISC_INTERNALS_OUT)/shared_flat_initfini.os \ $(MISC_INTERNALS_OUT)/shared_flat_add_library.os diff --git a/libc/misc/internals/reloc_static_pie.c b/libc/misc/internals/reloc_static_pie.c new file mode 100644 index 000000000..578202d23 --- /dev/null +++ b/libc/misc/internals/reloc_static_pie.c @@ -0,0 +1,47 @@ +/* Support for relocating static PIE. + Copyright (C) 2017-2022 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + <https://www.gnu.org/licenses/>. */ + +#include <link.h> +#include <elf.h> +#include <dl-elf.h> + +ElfW(Addr) _dl_load_base = NULL; + +void +reloc_static_pie (ElfW(Addr) load_addr); + +void +reloc_static_pie (ElfW(Addr) load_addr) +{ + ElfW(Word) relative_count = 0; + ElfW(Addr) rel_addr = 0; + ElfW(Dyn) * dyn_addr = NULL; + unsigned long dynamic_info[DYNAMIC_SIZE] = {0}; + + /* Read our own dynamic section and fill in the info array. */ + dyn_addr = ((void *) load_addr + elf_machine_dynamic ()); + + /* Use the underlying function to avoid TLS access before initialization */ + __dl_parse_dynamic_info(dyn_addr, dynamic_info, NULL, load_addr); + + /* Perform relocations */ + relative_count = dynamic_info[DT_RELCONT_IDX]; + rel_addr = dynamic_info[DT_RELOC_TABLE_ADDR]; + elf_machine_relative(load_addr, rel_addr, relative_count); + _dl_load_base = load_addr; +} diff --git a/libc/sysdeps/linux/arm/crt1.S b/libc/sysdeps/linux/arm/crt1.S index a1d7f0f23..fade1d25c 100644 --- a/libc/sysdeps/linux/arm/crt1.S +++ b/libc/sysdeps/linux/arm/crt1.S @@ -246,6 +246,22 @@ _start: mov lr, #0 #ifdef __ARCH_USE_MMU__ +#ifdef L_rcrt1 + /* We don't need to save a1 since no dynamic linker should have run */ + ldr a1, .L_GOT /* Get value at .L_GOT + 0 (offset to GOT)*/ + adr a2, .L_GOT /* Get address of .L_GOT */ + ldr a3, .L_GOT+16 /* Get value of _start(GOT) stored in .L_GOT */ + adr a4, _start /* Get address of _start after relocation (changes to pc - ~30 or so) */ + add a1, a1, a2 /* Calculate where the GOT is */ + ldr a2, [a1, a3] /* GOT + _start(GOT) = offset of _start from begin of file */ + sub a1, a4, a2 /* Current addr of _start - offset from beginning of file = load addr */ + bl reloc_static_pie + mov a1, #0 /* Clean up a1 so that a random address won't get called at the end of program */ + + /* Clear the frame pointer and link register again since it might be modified by previous call */ + mov fp, #0 + mov lr, #0 +#endif /* Pop argc off the stack and save a pointer to argv */ ldr a2, [sp], #4 mov a3, sp @@ -309,6 +325,9 @@ _start: .word _fini(GOT) .word _init(GOT) .word main(GOT) +#ifdef L_rcrt1 + .word _start(GOT) +#endif #endif #endif diff --git a/libc/sysdeps/linux/i386/crt1.S b/libc/sysdeps/linux/i386/crt1.S index 35a6552e8..decc68967 100644 --- a/libc/sysdeps/linux/i386/crt1.S +++ b/libc/sysdeps/linux/i386/crt1.S @@ -67,6 +67,9 @@ #endif .type main,%function .type __uClibc_main,%function +#ifdef L_rcrt1 +.type reloc_static_pie,%function +#endif _start: /* Clear the frame pointer. The ABI suggests this be done, to mark the outermost frame obviously. */ @@ -100,6 +103,23 @@ _start: pop %ebx addl $_GLOBAL_OFFSET_TABLE_+[.-.L0],%ebx +#ifdef L_rcrt1 + /* We cannot rely on _DYNAMIC being usable here due to RELRO. + Instead we calculate the load address based off a symbol + that we know will exist, _start. */ + pushl %ecx /* Save ecx so it won't get clobbered */ + pushl %ebx /* Save ebx so it won't get clobbered */ + xorl %ecx, %ecx /* Clear ecx */ + addl _start@GOT(%ebx), %ecx /* Get the offset of _start */ + movl _start@GOT(%ebx), %eax /* Get the run time address of _start */ + subl %ecx, %eax /* Subtract to find the load address */ + pushl %eax /* Pass the load address */ + call reloc_static_pie@PLT + popl %eax /* Clean up from function call */ + popl %ebx /* Restore the GOT address */ + popl %ecx /* restore ecx */ +#endif + /* Push address of our own entry points to .fini and .init. */ pushl _fini@GOT(%ebx) pushl _init@GOT(%ebx) diff --git a/libc/sysdeps/linux/x86_64/crt1.S b/libc/sysdeps/linux/x86_64/crt1.S index 87777dd5d..701cbf2f6 100644 --- a/libc/sysdeps/linux/x86_64/crt1.S +++ b/libc/sysdeps/linux/x86_64/crt1.S @@ -80,6 +80,20 @@ _start: the outermost frame obviously. */ xorl %ebp, %ebp +#ifdef L_rcrt1 + pushq %rdi /* save rdi (but should be 0...) */ + pushq %rdx /* store rdx (rtld_fini) */ + xorq %rcx, %rcx /* ensure rcx is 0 */ + addq _start@GOTPCREL(%rip), %rcx /* get offset of _start from beginning of file */ + movq _start@GOTPCREL(%rip), %rax /* get run time address of _start */ + subq %rcx, %rax /* calculate run time load offset */ + movq %rax, %rdi /* load offset -> param 1 */ + call reloc_static_pie /* relocate dynamic addrs */ + xorq %rax, %rax /* cleanup */ + popq %rdx + popq %rdi +#endif + /* Extract the arguments as encoded on the stack and set up the arguments for __libc_start_main (int (*main) (int, char **, char **), int argc, char *argv, @@ -107,7 +121,7 @@ _start: which grow downwards). */ pushq %rsp -#if defined(L_Scrt1) +#if defined(L_Scrt1) || defined(L_rcrt1) /* Give address for main() */ movq main@GOTPCREL(%rip), %rdi diff --git a/libpthread/nptl/sysdeps/generic/Makefile.in b/libpthread/nptl/sysdeps/generic/Makefile.in index eb656ee17..a5ba9bbe8 100644 --- a/libpthread/nptl/sysdeps/generic/Makefile.in +++ b/libpthread/nptl/sysdeps/generic/Makefile.in @@ -13,6 +13,10 @@ subdirs += libpthread/nptl/sysdeps/generic libpthread_generic_DIR := $(top_srcdir)libpthread/nptl/sysdeps/generic libpthread_generic_OUT := $(top_builddir)libpthread/nptl/sysdeps/generic +ifeq ($(STATIC_PIE),y) +CFLAGS-libc-tls.c := -DSTATIC_PIE +endif + libpthread_generic_libc_a_CSRC = libc-tls.c libpthread_generic_libc_a_COBJ = $(patsubst %.c,$(libpthread_generic_OUT)/%.o,$(libpthread_generic_libc_a_CSRC)) libpthread_generic_libc_a_OBJS = $(libpthread_generic_libc_a_COBJ) diff --git a/libpthread/nptl/sysdeps/generic/libc-tls.c b/libpthread/nptl/sysdeps/generic/libc-tls.c index d746c9a38..0c8c558d0 100644 --- a/libpthread/nptl/sysdeps/generic/libc-tls.c +++ b/libpthread/nptl/sysdeps/generic/libc-tls.c @@ -142,6 +142,10 @@ __libc_setup_tls (size_t tcbsize, size_t tcbalign) initimage = (void *) &__tdata_start; #else initimage = (void *) phdr->p_vaddr; +#if !defined(SHARED) && defined(STATIC_PIE) + extern ElfW(Addr) _dl_load_base; + initimage += _dl_load_base; +#endif #endif align = phdr->p_align; if (phdr->p_align > max_align) -- 2.34.1