[uclibc-ng-devel] Re: [Patch v3] Static PIE support for i386, x86_64, and arm

Hello, This is an updated patch for static pie support. I have corrected formatting and code standard issues which appeared in my previous patches. I also updated the commit message to be clearer on what is occurring and why. -linted From 92056b7db87be00e6daea59a4f82d022bfc7f223 Mon Sep 17 00:00:00 2001 From: linted &lt;linted(a)users.noreply.github.com&gt; Date: Sun, 17 Jul 2022 13:38:49 -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 elf headers, locating the dynamic section, and performing the relocations in a architecture agnostic method. This allows for easier porting of static-pie support to additional architectures. 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 | 41 ++++++++++++++++++++++++++  libc/sysdeps/linux/arm/crt1.S          | 15 ++++++++++  libc/sysdeps/linux/i386/crt1.S         | 20 +++++++++++++  libc/sysdeps/linux/x86_64/crt1.S       | 16 +++++++++-  7 files changed, 102 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..9a8066b84 --- /dev/null +++ b/libc/misc/internals/reloc_static_pie.c @@ -0,0 +1,41 @@ +/* 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> + +void +reloc_static_pie (ElfW(Addr) load_addr) +{ +    ElfW(Word) relative_count = 0; +    ElfW(Addr) rel_addr = NULL; +    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); +} diff --git a/libc/sysdeps/linux/arm/crt1.S b/libc/sysdeps/linux/arm/crt1.S index a1d7f0f23..2aa2a5234 100644 --- a/libc/sysdeps/linux/arm/crt1.S +++ b/libc/sysdeps/linux/arm/crt1.S @@ -246,6 +246,18 @@ _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 */ +#endif   /* Pop argc off the stack and save a pointer to argv */   ldr a2, [sp], #4   mov a3, sp @@ -309,6 +321,9 @@ _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 -- 2.34.1 _______________________________________________ devel mailing list --devel(a)uclibc-ng.org To unsubscribe send an email todevel-leave(a)uclibc-ng.org