From: Waldemar Kozaczuk <jwkozac...@gmail.com>
Committer: Nadav Har'El <n...@scylladb.com>
Branch: master
Allow running non-PIE executables that do not collide with kernel
This patch provides necessary changes to OSv dynamic linker
to allow running non-PIEs (Position Dependant Executables)
as long as they do not collide in virtual memory with kernel.
Fixes #190
Signed-off-by: Waldemar Kozaczuk <jwkozac...@gmail.com>
Message-Id: <20190621040947.29711-1-jwkozac...@gmail.com>
---
diff --git a/Makefile b/Makefile
--- a/Makefile
+++ b/Makefile
@@ -312,7 +312,8 @@ gcc-sysroot = $(if $(CROSS_PREFIX), --sysroot
external/$(arch)/gcc.bin) \
# To add something that will *not* be part of the main kernel, you can do:
#
# mydir/*.o EXTRA_FLAGS = <MY_STUFF>
-EXTRA_FLAGS = -D__OSV_CORE__ -DOSV_KERNEL_BASE=$(kernel_base)
-DOSV_KERNEL_VM_SHIFT=$(kernel_vm_shift)
-DOSV_LZKERNEL_BASE=$(lzkernel_base)
+EXTRA_FLAGS = -D__OSV_CORE__ -DOSV_KERNEL_BASE=$(kernel_base)
-DOSV_KERNEL_VM_BASE=$(kernel_vm_base) \
+ -DOSV_KERNEL_VM_SHIFT=$(kernel_vm_shift)
-DOSV_LZKERNEL_BASE=$(lzkernel_base)
EXTRA_LIBS =
COMMON = $(autodepend) -g -Wall -Wno-pointer-arith $(CFLAGS_WERROR)
-Wformat=0 -Wno-format-security \
-D __BSD_VISIBLE=1 -U _FORTIFY_SOURCE -fno-stack-protector $(INCLUDES) \
diff --git a/core/elf.cc b/core/elf.cc
--- a/core/elf.cc
+++ b/core/elf.cc
@@ -34,6 +34,9 @@ TRACEPOINT(trace_elf_unload, "%s", const char *);
TRACEPOINT(trace_elf_lookup, "%s", const char *);
TRACEPOINT(trace_elf_lookup_addr, "%p", const void *);
+extern void* elf_start;
+extern size_t elf_size;
+
using namespace boost::range;
namespace {
@@ -224,7 +227,6 @@ memory_image::memory_image(program& prog, void* base)
auto p = static_cast<Elf64_Phdr*>(base + _ehdr.e_phoff);
assert(_ehdr.e_phentsize == sizeof(*p));
_phdrs.assign(p, p + _ehdr.e_phnum);
- set_base(base);
}
void memory_image::load_segment(const Elf64_Phdr& phdr)
@@ -267,14 +269,9 @@ void file::load_elf_header()
|| _ehdr.e_ident[EI_OSABI] == 0)) {
throw osv::invalid_elf_error("bad os abi");
}
- // We currently only support running ET_DYN objects (shared library or
- // position-independent executable). In the future we can add support
for
- // ET_EXEC (ordinary, position-dependent executables) but it will
require
- // loading them at their specified address and moving the kernel out of
- // their way.
- if (_ehdr.e_type != ET_DYN) {
+ if (!(_ehdr.e_type == ET_DYN || _ehdr.e_type == ET_EXEC)) {
throw osv::invalid_elf_error(
- "bad executable type (only shared-object or PIE
supported)");
+ "bad executable type (only shared-object, PIE or non-PIE
executable supported)");
}
}
@@ -297,17 +294,37 @@ void* align(void* addr, ulong align, ulong offset)
}
+static bool intersects_with_kernel(Elf64_Addr elf_addr)
+{
+ void *addr = reinterpret_cast<void*>(elf_addr);
+ return addr >= elf_start && addr < elf_start + elf_size;
+}
+
void object::set_base(void* base)
{
auto p = std::min_element(_phdrs.begin(), _phdrs.end(),
[](Elf64_Phdr a, Elf64_Phdr b)
{ return a.p_type == PT_LOAD
&& a.p_vaddr < b.p_vaddr; });
- _base = align(base, p->p_align, p->p_vaddr & (p->p_align - 1)) -
p->p_vaddr;
auto q = std::min_element(_phdrs.begin(), _phdrs.end(),
[](Elf64_Phdr a, Elf64_Phdr b)
{ return a.p_type == PT_LOAD
&& a.p_vaddr > b.p_vaddr; });
+
+ if (!is_core() && is_non_pie_executable()) {
+ // Verify non-PIE executable does not collide with the kernel
+ if (intersects_with_kernel(p->p_vaddr) ||
intersects_with_kernel(q->p_vaddr + q->p_memsz)) {
+ abort("Non-PIE executable [%s] collides with kernel:
[%p-%p] !\n",
+ pathname().c_str(), p->p_vaddr, q->p_vaddr +
q->p_memsz);
+ }
+ // Override the passed in value as the base for non-PIEs (Position
Dependant Executables)
+ // needs to be set to 0 because all the addresses in it are
absolute
+ _base = 0x0;
+ } else {
+ // Otherwise for kernel, PIEs and shared libraries set the base as
requested by caller
+ _base = align(base, p->p_align, p->p_vaddr & (p->p_align - 1)) -
p->p_vaddr;
+ }
+
_end = _base + q->p_vaddr + q->p_memsz;
}
@@ -447,6 +464,9 @@ void object::load_segments()
abort("Unknown p_type in executable %s: %d\n", pathname(),
phdr.p_type);
}
}
+ if (!is_core() && _ehdr.e_type == ET_EXEC && !_is_executable) {
+ abort("Statically linked executables are not supported!\n");
+ }
// As explained in issue #352, we currently don't correctly support TLS
// used in PIEs.
if (_is_executable && _tls_segment) {
@@ -1099,7 +1119,9 @@ void create_main_program()
program::program(void* addr)
: _next_alloc(addr)
{
- _core = std::make_shared<memory_image>(*this, (void*)(ELF_IMAGE_START
+ OSV_KERNEL_VM_SHIFT));
+ void *program_base = (void*)(ELF_IMAGE_START + OSV_KERNEL_VM_SHIFT);
+ _core = std::make_shared<memory_image>(*this, program_base);
+ _core->set_base(program_base);
assert(_core->module_index() == core_module_index);
_core->load_segments();
set_search_path({"/", "/usr/lib"});
@@ -1223,7 +1245,8 @@ program::load_object(std::string name,
std::vector<std::string> extra_path,
_modules_rcu.assign(new_modules.release());
osv::rcu_dispose(old_modules);
ef->load_segments();
- _next_alloc = ef->end();
+ if (!ef->is_non_pie_executable())
+ _next_alloc = ef->end();
add_debugger_obj(ef.get());
loaded_objects.push_back(ef);
ef->load_needed(loaded_objects);
diff --git a/include/osv/elf.hh b/include/osv/elf.hh
--- a/include/osv/elf.hh
+++ b/include/osv/elf.hh
@@ -365,6 +365,7 @@ public:
void init_static_tls();
size_t initial_tls_size() { return _initial_tls_size; }
void* initial_tls() { return _initial_tls.get(); }
+ bool is_non_pie_executable() { return _ehdr.e_type == ET_EXEC; }
std::vector<ptrdiff_t>& initial_tls_offsets() { return
_initial_tls_offsets; }
protected:
virtual void load_segment(const Elf64_Phdr& segment) = 0;
diff --git a/modules/tests/Makefile b/modules/tests/Makefile
--- a/modules/tests/Makefile
+++ b/modules/tests/Makefile
@@ -67,7 +67,11 @@ $(out)/tests/tst-getopt-pie.o: $(src)/tests/tst-getopt.cc
$(makedir)
$(call quiet, $(CXX) $(CXXFLAGS) -c -o $@ $<, CXX $*.cc)
$(out)/tests/tst-getopt-pie.so: $(out)/tests/tst-getopt-pie.o
- $(call quiet, $(CXX) $(CXXFLAGS) -pie -o $@ $< $(LIBS), LD $*.so)
+ $(call quiet, $(CXX) $(CXXFLAGS) -pie -o $@ $< $(LIBS), LD $@)
+
+$(out)/tests/tst-non-pie.so: CXXFLAGS:=$(subst -fPIC,-no-pie,$(CXXFLAGS))
+$(out)/tests/tst-non-pie.so: $(src)/tests/tst-non-pie.cc
+ $(call quiet, $(CXX) $(CXXFLAGS) -o $@ $< $(LIBS), LD $@)
# The rofs test image mounts /tmp as ramfs and 4 tests that exercise file
system
# fail due to some unresolved bugs or other shortcomings of the ramfs
implementation
@@ -124,7 +128,7 @@ tests := tst-pthread.so misc-ramdisk.so tst-vblk.so
tst-bsd-evh.so \
tst-ttyname.so tst-pthread-barrier.so tst-feexcept.so tst-math.so \
tst-sigaltstack.so tst-fread.so tst-tcp-cork.so tst-tcp-v6.so \
tst-calloc.so tst-crypt.so tst-non-fpic.so tst-small-malloc.so \
- tst-mmx-fpu.so tst-getopt.so tst-getopt-pie.so
+ tst-mmx-fpu.so tst-getopt.so tst-getopt-pie.so tst-non-pie.so
# libstatic-thread-variable.so tst-static-thread-variable.so \
tests += testrunner.so
diff --git a/tests/tst-non-pie.cc b/tests/tst-non-pie.cc
--- a/tests/tst-non-pie.cc
+++ b/tests/tst-non-pie.cc
@@ -0,0 +1,6 @@
+#include <stdio.h>
+
+int main(){
+ printf("Hello from C code\n");
+ return 0;
+}
--
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