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Kernel: Switch to eagerly restoring x86 FPU state on context switch

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Lazy FPU restore is well known to be vulnerable to timing attacks,
and eager restore is a lot simpler anyway, so let's just do it eagerly.
This commit is contained in:
Andreas Kling 2020-01-01 16:49:08 +01:00
parent 9c0836ce97
commit fd740829d1
5 changed files with 15 additions and 39 deletions
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14
Kernel/Thread.cpp
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@ -10,6 +10,8 @@
//#define SIGNAL_DEBUG
static FPUState s_clean_fpu_state;
u16 thread_specific_selector()
{
static u16 selector;
@ -55,7 +57,7 @@ Thread::Thread(Process& process)
dbgprintf("Thread{%p}: New thread TID=%u in %s(%u)\n", this, m_tid, process.name().characters(), process.pid());
set_default_signal_dispositions();
m_fpu_state = (FPUState*)kmalloc_aligned(sizeof(FPUState), 16);
memset(m_fpu_state, 0, sizeof(FPUState));
memcpy(m_fpu_state, &s_clean_fpu_state, sizeof(FPUState));
memset(&m_tss, 0, sizeof(m_tss));
// Only IF is set when a process boots.
@ -119,9 +121,6 @@ Thread::~Thread()
thread_table().remove(this);
}
if (g_last_fpu_thread == this)
g_last_fpu_thread = nullptr;
if (selector())
gdt_free_entry(selector());
@ -625,8 +624,7 @@ u32 Thread::make_userspace_stack_for_main_thread(Vector<String> arguments, Vecto
}
env[environment.size()] = nullptr;
auto push_on_new_stack = [&new_esp](u32 value)
{
auto push_on_new_stack = [&new_esp](u32 value) {
new_esp -= 4;
u32* stack_ptr = (u32*)new_esp;
*stack_ptr = value;
@ -646,7 +644,6 @@ Thread* Thread::clone(Process& process)
memcpy(clone->m_signal_action_data, m_signal_action_data, sizeof(m_signal_action_data));
clone->m_signal_mask = m_signal_mask;
memcpy(clone->m_fpu_state, m_fpu_state, sizeof(FPUState));
clone->m_has_used_fpu = m_has_used_fpu;
clone->m_thread_specific_data = m_thread_specific_data;
return clone;
}
@ -654,6 +651,9 @@ Thread* Thread::clone(Process& process)
void Thread::initialize()
{
Scheduler::initialize();
asm volatile("fninit");
asm volatile("fxsave %0"
: "=m"(s_clean_fpu_state));
}
Vector<Thread*> Thread::all_threads()