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Kernel: Shrink instead of expand sigaltstack range to page boundaries

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Since the POSIX sigaltstack manpage suggests allocating the stack
region using malloc(), and many heap implementations (including ours)
store heap chunk metadata in memory just before the vended pointer,
we would end up zeroing the metadata, leading to various crashes.
This commit is contained in:
Idan Horowitz 2023-12-24 15:53:16 +02:00 • committed by Andreas Kling
parent 4c6fd454d0
commit a49b7e92eb
5 changed files with 29 additions and 34 deletions
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38
Kernel/Syscalls/sigaction.cpp
View file

@ -117,17 +117,20 @@ ErrorOr<FlatPtr> Process::sys$sigreturn(RegisterState& registers)
return saved_ax;
}
ErrorOr<void> Process::remap_range_as_stack(FlatPtr address, size_t size)
ErrorOr<Memory::VirtualRange> Process::remap_range_as_stack(FlatPtr address, size_t size)
{
// FIXME: This duplicates a lot of logic from sys$mprotect, this should be abstracted out somehow
auto range_to_remap = TRY(Memory::expand_range_to_page_boundaries(address, size));
// NOTE: We shrink the given range to page boundaries (instead of expanding it), as sigaltstack's manpage suggests
// using malloc() to allocate the stack region, and many heap implementations (including ours) store heap chunk
// metadata in memory just before the vended pointer, which we would end up zeroing.
auto range_to_remap = TRY(Memory::shrink_range_to_page_boundaries(address, size));
if (!range_to_remap.size())
return EINVAL;
if (!is_user_range(range_to_remap))
return EFAULT;
return address_space().with([&](auto& space) -> ErrorOr<void> {
return address_space().with([&](auto& space) -> ErrorOr<Memory::VirtualRange> {
if (auto* whole_region = space->find_region_from_range(range_to_remap)) {
if (!whole_region->is_mmap())
return EPERM;
@ -141,7 +144,7 @@ ErrorOr<void> Process::remap_range_as_stack(FlatPtr address, size_t size)
whole_region->clear_to_zero();
whole_region->remap();
return {};
return range_to_remap;
}
if (auto* old_region = space->find_region_containing(range_to_remap)) {
@ -174,7 +177,7 @@ ErrorOr<void> Process::remap_range_as_stack(FlatPtr address, size_t size)
}
TRY(new_region->map(space->page_directory()));
return {};
return range_to_remap;
}
if (auto const& regions = TRY(space->find_regions_intersecting(range_to_remap)); regions.size()) {
@ -235,7 +238,7 @@ ErrorOr<void> Process::remap_range_as_stack(FlatPtr address, size_t size)
TRY(new_region->map(space->page_directory()));
}
return {};
return range_to_remap;
}
return EINVAL;
@ -249,13 +252,16 @@ ErrorOr<FlatPtr> Process::sys$sigaltstack(Userspace<stack_t const*> user_ss, Use
if (user_old_ss) {
stack_t old_ss_value {};
old_ss_value.ss_sp = (void*)Thread::current()->m_alternative_signal_stack;
old_ss_value.ss_size = Thread::current()->m_alternative_signal_stack_size;
old_ss_value.ss_flags = 0;
if (!Thread::current()->has_alternative_signal_stack())
if (Thread::current()->m_alternative_signal_stack.has_value()) {
old_ss_value.ss_sp = Thread::current()->m_alternative_signal_stack->base().as_ptr();
old_ss_value.ss_size = Thread::current()->m_alternative_signal_stack->size();
if (Thread::current()->is_in_alternative_signal_stack())
old_ss_value.ss_flags = SS_ONSTACK;
else
old_ss_value.ss_flags = 0;
} else {
old_ss_value.ss_flags = SS_DISABLE;
else if (Thread::current()->is_in_alternative_signal_stack())
old_ss_value.ss_flags = SS_ONSTACK;
}
TRY(copy_to_user(user_old_ss, &old_ss_value));
}
@ -266,8 +272,7 @@ ErrorOr<FlatPtr> Process::sys$sigaltstack(Userspace<stack_t const*> user_ss, Use
return EPERM;
if (ss.ss_flags == SS_DISABLE) {
Thread::current()->m_alternative_signal_stack_size = 0;
Thread::current()->m_alternative_signal_stack = 0;
Thread::current()->m_alternative_signal_stack.clear();
} else if (ss.ss_flags == 0) {
if (ss.ss_size <= MINSIGSTKSZ)
return ENOMEM;
@ -278,10 +283,7 @@ ErrorOr<FlatPtr> Process::sys$sigaltstack(Userspace<stack_t const*> user_ss, Use
// protections, sigaltstack ranges are carved out of their regions, zeroed, and
// turned into read/writable MAP_STACK-enabled regions.
// This is inspired by OpenBSD's solution: https://man.openbsd.org/sigaltstack.2
TRY(remap_range_as_stack((FlatPtr)ss.ss_sp, ss.ss_size));
Thread::current()->m_alternative_signal_stack = (FlatPtr)ss.ss_sp;
Thread::current()->m_alternative_signal_stack_size = ss.ss_size;
Thread::current()->m_alternative_signal_stack = TRY(remap_range_as_stack((FlatPtr)ss.ss_sp, ss.ss_size));
} else {
return EINVAL;
}