16 Jul
2022
16 Jul
'22
8:46 p.m.
I did a little bit of research, and you are completely right, I should have
been using DYNAMIC_SIZE rather than the static 36. I'm not entirely sure
what to do about the format of the comments. It seems to be a tabs vs
spaces issue. Both files swap between tabs and spaces in different places
throughout the file. I think that if I swap over to spaces it might make it
look a little cleaner though. I'll resubmit with the other changes you
suggested.
On Sat, Jul 16, 2022 at 5:27 AM Yann Sionneau <yann(a)sionneau.net> wrote:
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(a)gmail.com>
Date :
15/07/2022, 22:26
Pour :
devel(a)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: linted<linted(a)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: linted<linted(a)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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