[PATCH v2 12/18] x86/espfix/64: Stop assuming that pt_regs is on the entry stack

[Andy Lutomirski]

When we start using an entry trampoline, a #GP from userspace will
be delivered on the entry stack, not on the task stack.  Fix the
espfix64 #DF fixup to set up #GP according to TSS.SP0, rather than
assuming that pt_regs + 1 == SP0.  This won't change anything
without an entry stack, but it will make the code continue to work
when an entry stack is added.

Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
---
 arch/x86/kernel/traps.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 81841f27beff..1ea03027a4a9 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -358,7 +358,8 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code)
 		regs->cs == __KERNEL_CS &&
 		regs->ip == (unsigned long)native_irq_return_iret)
 	{
-		struct pt_regs *normal_regs = task_pt_regs(current);
+		struct pt_regs *normal_regs =
+			(struct pt_regs *)this_cpu_read(cpu_tss.x86_tss.sp0) - 1;
 
 		/* Fake a #GP(0) from userspace. */
 		memmove(&normal_regs->ip, (void *)regs->sp, 5*8);
@@ -389,7 +390,7 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code)
 	 *
 	 *   Processors update CR2 whenever a page fault is detected. If a
 	 *   second page fault occurs while an earlier page fault is being
-	 *   deliv- ered, the faulting linear address of the second fault will
+	 *   delivered, the faulting linear address of the second fault will
 	 *   overwrite the contents of CR2 (replacing the previous
 	 *   address). These updates to CR2 occur even if the page fault
 	 *   results in a double fault or occurs during the delivery of a
-- 
2.13.6