[RFC][PATCH 18/24] x86/pti: Execute system vector handlers on the kernel stack

[Alexandre Chartre <alexandre.chartre@oracle.com>]

After an interrupt/exception in userland, the kernel is entered
and it switches the stack to the PTI stack which is mapped both in
the kernel and in the user page-table. When executing the interrupt
function, switch to the kernel stack (which is mapped only in the
kernel page-table) so that no kernel data leak to the userland
through the stack.

Changes system vector handlers to execute on the kernel stack.

Signed-off-by: Alexandre Chartre <alexandre.chartre@oracle.com>
---
 arch/x86/include/asm/idtentry.h | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
index a82e31b45442..0c5d9f027112 100644
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -66,6 +66,17 @@ void run_idt_errcode(void (*func)(struct pt_regs *, unsigned long),
 	CALL_ON_STACK_2(pti_kernel_stack(regs), func, regs, error_code);
 }
 
+static __always_inline
+void run_sysvec(void (*func)(struct pt_regs *regs), struct pt_regs *regs)
+{
+	void *stack = pti_kernel_stack(regs);
+
+	if (stack)
+		asm_call_on_stack_1(stack, (void (*)(void))func, regs);
+	else
+		run_sysvec_on_irqstack_cond(func, regs);
+}
+
 /**
  * DECLARE_IDTENTRY - Declare functions for simple IDT entry points
  *		      No error code pushed by hardware
@@ -295,7 +306,7 @@ __visible noinstr void func(struct pt_regs *regs)			\
 	instrumentation_begin();					\
 	irq_enter_rcu();						\
 	kvm_set_cpu_l1tf_flush_l1d();					\
-	run_sysvec_on_irqstack_cond(__##func, regs);			\
+	run_sysvec(__##func, regs);					\
 	irq_exit_rcu();							\
 	instrumentation_end();						\
 	irqentry_exit(regs, state);					\
-- 
2.18.4