[uclibc-ng-devel] Re: [Patch v2] Static PIE support for i386, x86_64, and arm

Hello,

Looks great :)

Comments inline:

Le 15/07/2022 à 22:26, linted a écrit :

Sujet : [uclibc-ng-devel] [Patch v2] Static PIE support for i386, x86_64, and arm De : linted linted90@gmail.com Date : 15/07/2022, 22:26

Pour : devel@uclibc-ng.org

Hello, This is an updated patch for static pie support on i386, x86_64, and arm. I added dependency checks to ensure it only affects supported architectures. I also added a check to ensure an MMU is present on arm since there is no support for FDPIC yet.

0001-Added-static-pie-support-for-i368-x86_64-and-arm.patch

From 98313d17220486a75a0e552df045c6752a5ad25b Mon Sep 17 00:00:00 2001 From: lintedlinted@users.noreply.github.com Date: Fri, 15 Jul 2022 16:15:14 -0400 Subject: [PATCH] Added static pie support for i368, x86_64 and arm

Maybe add some more description of how this is done in the commit message?

Signed-off-by: lintedlinted@users.noreply.github.com

Makerules | 5 ++++ extra/Configs/Config.in | 7 ++++- libc/misc/internals/Makefile.in | 1 + libc/misc/internals/reloc_static_pie.c | 39 ++++++++++++++++++++++++++ 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, 101 insertions(+), 2 deletions(-) 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..ac5c494c3 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

@@ -1757,7 +1762,7 @@ config UCLIBC_HAS_STDIO_AUTO_RW_TRANSITION fflush function or to a file positioning function (fseek, fsetpos, or rewind), and input shall not be directly followed by output without an intervening call to a file positioning function, unless the input

•  operation encounters end�of�file.
  

•  operation encounters end�of�file.
  

This seems like a spurious modification due to the text editor?

 Most people will answer Y.

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..0736bc8a1 --- /dev/null +++ b/libc/misc/internals/reloc_static_pie.c @@ -0,0 +1,39 @@ +/* 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) +{

• /* Read our own dynamic section and fill in the info array. */
• ElfW(Dyn) * dyn_addr = ((void *) load_addr + elf_machine_dynamic ());
• unsigned long dynamic_info[36] = {0};

Could you use some generic define for the size of dynamic_info instead of the hard coded 36?

Like DYNAMIC_SIZE for instance? (I haven't checked if it's the correct value for you)

• /* Use the underlying function to avoid TLS access before initialization */
• __dl_parse_dynamic_info(dyn_addr, dynamic_info, NULL, load_addr);
• ElfW(Word) relative_count = dynamic_info[DT_RELCONT_IDX];
• ElfW(Addr) rel_addr = dynamic_info[DT_RELOC_TABLE_ADDR];

Maybe declare relative_count and rel_addr at the beginning of the function?

• elf_machine_relative(load_addr, rel_addr, relative_count);
• return;

I would remove the return.

+} diff --git a/libc/sysdeps/linux/arm/crt1.S b/libc/sysdeps/linux/arm/crt1.S index a1d7f0f23..adaf4b983 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..4e4cef3ce 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. */
  

nitpick: the comments of the assembly code for arm crt1.S are well aligned whereas those for i386/x86_64 are not well aligned.

• 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..04536d07f 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

---

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0001-Added-static-pie-support-for-i368-x86_64-and-arm.patch 8,2 Ko