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LibELF: Only call IFUNC resolvers after populating the PLT

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As IFUNC resolvers may call arbitrary functions though the PLT, they can
only be called after the PLT has been populated. This is true of the
`[[gnu::target_clones]]` attribute, which makes a call to
`__cpu_indicator_init`, which is defined in `libgcc_s.so`, through the
PLT.

`do_plt_relocation` and `do_direct_relocation` are given a parameter
that controls whether IFUNCs are immediately resolved. In the first
pass, relocations pointing to IFUNCs are put on a worklist, while all
other relocations are performed. Only after non-IFUNC relocations are
done and the PLT is set up do we deal with these.
This commit is contained in:
Daniel Bertalan 2023-04-22 12:09:00 +02:00 • committed by Andreas Kling
parent cd45c2d295
commit e2b1f9447c
2 changed files with 53 additions and 15 deletions
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51
Userland/Libraries/LibELF/DynamicLoader.cpp
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@ -203,39 +203,47 @@ void DynamicLoader::do_main_relocations()
do_relr_relocations();
m_dynamic_object->relocation_section().for_each_relocation([&](DynamicObject::Relocation const& relocation) {
switch (do_direct_relocation(relocation, ShouldInitializeWeak::No)) {
switch (do_direct_relocation(relocation, ShouldInitializeWeak::No, ShouldCallIfuncResolver::No)) {
case RelocationResult::Failed:
dbgln("Loader.so: {} unresolved symbol '{}'", m_filepath, relocation.symbol().name());
VERIFY_NOT_REACHED();
case RelocationResult::ResolveLater:
m_unresolved_relocations.append(relocation);
break;
case RelocationResult::CallIfuncResolver:
m_direct_ifunc_relocations.append(relocation);
break;
case RelocationResult::Success:
break;
}
});
// If the object is position-independent, the pointer to the PLT trampoline needs to be relocated.
auto fixup_trampoline_pointer = [&](DynamicObject::Relocation const& relocation) {
VERIFY(relocation.type() == R_X86_64_JUMP_SLOT || relocation.type() == R_AARCH64_JUMP_SLOT);
if (image().is_dynamic())
*((FlatPtr*)relocation.address().as_ptr()) += m_dynamic_object->base_address().get();
};
// FIXME: Or LD_BIND_NOW is set?
if (m_dynamic_object->must_bind_now()) {
m_dynamic_object->plt_relocation_section().for_each_relocation([&](DynamicObject::Relocation const& relocation) {
RelocationResult result;
if (relocation.type() == R_X86_64_IRELATIVE || relocation.type() == R_AARCH64_IRELATIVE) {
result = do_direct_relocation(relocation, ShouldInitializeWeak::No);
} else {
result = do_plt_relocation(relocation);
m_direct_ifunc_relocations.append(relocation);
return;
}
switch (result) {
switch (do_plt_relocation(relocation, ShouldCallIfuncResolver::No)) {
case RelocationResult::Failed:
dbgln("Loader.so: {} unresolved symbol '{}'", m_filepath, relocation.symbol().name());
VERIFY_NOT_REACHED();
case RelocationResult::ResolveLater:
VERIFY_NOT_REACHED();
case RelocationResult::CallIfuncResolver:
m_plt_ifunc_relocations.append(relocation);
// Set up lazy binding, in case an IFUNC resolver calls another IFUNC that hasn't been resolved yet.
fixup_trampoline_pointer(relocation);
break;
case RelocationResult::Success:
break;
}
@ -243,7 +251,7 @@ void DynamicLoader::do_main_relocations()
} else {
m_dynamic_object->plt_relocation_section().for_each_relocation([&](DynamicObject::Relocation const& relocation) {
if (relocation.type() == R_X86_64_IRELATIVE || relocation.type() == R_AARCH64_IRELATIVE) {
do_direct_relocation(relocation, ShouldInitializeWeak::No);
m_direct_ifunc_relocations.append(relocation);
return;
}
fixup_trampoline_pointer(relocation);
@ -259,6 +267,18 @@ Result<NonnullRefPtr<DynamicObject>, DlErrorMessage> DynamicLoader::load_stage_3
setup_plt_trampoline();
}
// IFUNC resolvers can only be called after the PLT has been populated,
// as they may call arbitrary functions via the PLT.
for (auto const& relocation : m_plt_ifunc_relocations) {
auto result = do_plt_relocation(relocation, ShouldCallIfuncResolver::Yes);
VERIFY(result == RelocationResult::Success);
}
for (auto const& relocation : m_direct_ifunc_relocations) {
auto result = do_direct_relocation(relocation, ShouldInitializeWeak::No, ShouldCallIfuncResolver::Yes);
VERIFY(result == RelocationResult::Success);
}
if (m_dynamic_object->has_text_relocations()) {
// If we don't have textrels, .text has already been made executable by this point in load_stage_2.
for (auto& text_segment : m_text_segments) {
@ -295,7 +315,7 @@ void DynamicLoader::load_stage_4()
void DynamicLoader::do_lazy_relocations()
{
for (auto const& relocation : m_unresolved_relocations) {
if (auto res = do_direct_relocation(relocation, ShouldInitializeWeak::Yes); res != RelocationResult::Success) {
if (auto res = do_direct_relocation(relocation, ShouldInitializeWeak::Yes, ShouldCallIfuncResolver::Yes); res != RelocationResult::Success) {
dbgln("Loader.so: {} unresolved symbol '{}'", m_filepath, relocation.symbol().name());
VERIFY_NOT_REACHED();
}
@ -495,7 +515,7 @@ void DynamicLoader::load_program_headers()
}
}
DynamicLoader::RelocationResult DynamicLoader::do_direct_relocation(DynamicObject::Relocation const& relocation, ShouldInitializeWeak should_initialize_weak)
DynamicLoader::RelocationResult DynamicLoader::do_direct_relocation(DynamicObject::Relocation const& relocation, ShouldInitializeWeak should_initialize_weak, ShouldCallIfuncResolver should_call_ifunc_resolver)
{
FlatPtr* patch_ptr = nullptr;
if (is_dynamic())
@ -523,6 +543,9 @@ DynamicLoader::RelocationResult DynamicLoader::do_direct_relocation(DynamicObjec
dbgln("ERROR: symbol not found: {}.", symbol.name());
return RelocationResult::Failed;
}
if (res.value().type == STT_GNU_IFUNC && should_call_ifunc_resolver == ShouldCallIfuncResolver::No)
return RelocationResult::CallIfuncResolver;
auto symbol_address = res.value().address;
if (relocation.addend_used())
*patch_ptr = symbol_address.get() + relocation.addend();
@ -550,6 +573,8 @@ DynamicLoader::RelocationResult DynamicLoader::do_direct_relocation(DynamicObjec
} else {
symbol_location = res.value().address;
if (res.value().type == STT_GNU_IFUNC) {
if (should_call_ifunc_resolver == ShouldCallIfuncResolver::No)
return RelocationResult::CallIfuncResolver;
if (res.value().dynamic_object != nullptr && res.value().dynamic_object->has_text_relocations()) {
dbgln("\033[31mError:\033[0m Refusing to call IFUNC resolver defined in an object with text relocations.");
return RelocationResult::Failed;
@ -602,6 +627,8 @@ DynamicLoader::RelocationResult DynamicLoader::do_direct_relocation(DynamicObjec
}
case R_AARCH64_IRELATIVE:
case R_X86_64_IRELATIVE: {
if (should_call_ifunc_resolver == ShouldCallIfuncResolver::No)
return RelocationResult::CallIfuncResolver;
VirtualAddress resolver;
if (relocation.addend_used())
resolver = m_dynamic_object->base_address().offset(relocation.addend());
@ -627,7 +654,7 @@ DynamicLoader::RelocationResult DynamicLoader::do_direct_relocation(DynamicObjec
return RelocationResult::Success;
}
DynamicLoader::RelocationResult DynamicLoader::do_plt_relocation(DynamicObject::Relocation const& relocation)
DynamicLoader::RelocationResult DynamicLoader::do_plt_relocation(DynamicObject::Relocation const& relocation, ShouldCallIfuncResolver should_call_ifunc_resolver)
{
VERIFY(relocation.type() == R_X86_64_JUMP_SLOT || relocation.type() == R_AARCH64_JUMP_SLOT);
auto symbol = relocation.symbol();
@ -638,6 +665,8 @@ DynamicLoader::RelocationResult DynamicLoader::do_plt_relocation(DynamicObject::
auto address = result.value().address;
if (result.value().type == STT_GNU_IFUNC) {
if (should_call_ifunc_resolver == ShouldCallIfuncResolver::No)
return RelocationResult::CallIfuncResolver;
symbol_location = VirtualAddress { reinterpret_cast<DynamicObject::IfuncResolver>(address.get())() };
} else {
symbol_location = address;
@ -701,7 +730,7 @@ void DynamicLoader::setup_plt_trampoline()
extern "C" FlatPtr _fixup_plt_entry(DynamicObject* object, u32 relocation_offset)
{
auto const& relocation = object->plt_relocation_section().relocation_at_offset(relocation_offset);
auto result = DynamicLoader::do_plt_relocation(relocation);
auto result = DynamicLoader::do_plt_relocation(relocation, ShouldCallIfuncResolver::Yes);
if (result != DynamicLoader::RelocationResult::Success) {
dbgln("Loader.so: {} unresolved symbol '{}'", object->filepath(), relocation.symbol().name());
VERIFY_NOT_REACHED();