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Kernel: Don't keep protected Process data in a separate allocation

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The previous architecture had a huge flaw: the pointer to the protected
data was itself unprotected, allowing you to overwrite it at any time.

This patch reorganizes the protected data so it's part of the Process
class itself. (Actually, it's a new ProcessBase helper class.)

We use the first 4 KB of Process objects themselves as the new storage
location for protected data. Then we make Process objects page-aligned
using MAKE_ALIGNED_ALLOCATED.

This allows us to easily turn on/off write-protection for everything in
the ProcessBase portion of Process. :^)

Thanks to @bugaevc for pointing out the flaw! This is still not perfect
but it's an improvement.
This commit is contained in:
Andreas Kling 2021-03-11 13:13:05 +01:00
parent 4fcc637e29
commit 90c0f9664e
10 changed files with 125 additions and 125 deletions
Download patch file Download diff file Expand all files Collapse all files

46
Kernel/Process.cpp
View file

@ -209,27 +209,14 @@ RefPtr<Process> Process::create_kernel_process(RefPtr<Thread>& first_thread, Str
return process;
}
const Process::ProtectedData& Process::protected_data() const
{
return *reinterpret_cast<const ProtectedData*>(m_protected_data->data());
}
void Process::protect_data()
{
auto& region = m_protected_data->impl().region();
if (!region.is_writable())
return;
region.set_writable(false);
region.remap();
MM.set_page_writable_direct(VirtualAddress { this }, false);
}
void Process::unprotect_data()
{
auto& region = m_protected_data->impl().region();
if (region.is_writable())
return;
region.set_writable(true);
region.remap();
MM.set_page_writable_direct(VirtualAddress { this }, true);
}
Process::Process(RefPtr<Thread>& first_thread, const String& name, uid_t uid, gid_t gid, ProcessID ppid, bool is_kernel_process, RefPtr<Custody> cwd, RefPtr<Custody> executable, TTY* tty, Process* fork_parent)
@ -240,20 +227,14 @@ Process::Process(RefPtr<Thread>& first_thread, const String& name, uid_t uid, gi
, m_tty(tty)
, m_wait_block_condition(*this)
{
m_protected_data = KBuffer::try_create_with_size(sizeof(ProtectedData));
VERIFY(m_protected_data);
{
MutableProtectedData protected_data { *this };
protected_data->pid = allocate_pid();
protected_data->ppid = ppid;
protected_data->uid = uid;
protected_data->gid = gid;
protected_data->euid = uid;
protected_data->egid = gid;
protected_data->suid = uid;
protected_data->sgid = gid;
}
m_pid = allocate_pid();
m_ppid = ppid;
m_uid = uid;
m_gid = gid;
m_euid = uid;
m_egid = gid;
m_suid = uid;
m_sgid = gid;
dbgln_if(PROCESS_DEBUG, "Created new process {}({})", m_name, this->pid().value());
@ -273,6 +254,8 @@ Process::Process(RefPtr<Thread>& first_thread, const String& name, uid_t uid, gi
Process::~Process()
{
unprotect_data();
VERIFY(thread_count() == 0); // all threads should have been finalized
VERIFY(!m_alarm_timer);
@ -727,9 +710,10 @@ bool Process::add_thread(Thread& thread)
void Process::set_dumpable(bool dumpable)
{
if (dumpable == protected_data().dumpable)
if (dumpable == m_dumpable)
return;
MutableProtectedData(*this)->dumpable = dumpable;
ProtectedDataMutationScope scope { *this };
m_dumpable = dumpable;
}
}