From: Andy Lutomirski <luto@kernel.org>
Date: Thu, 2 Nov 2017 00:59:15 -0700
Subject: x86/entry/32: Fix cpu_current_top_of_stack initialization at boot
Git-commit: cd493a6deb8b78eca280d05f7fa73fd69403ae29
Patch-mainline: v4.15-rc1
References: bsc#1068032 CVE-2017-5754

cpu_current_top_of_stack's initialization forgot about
TOP_OF_KERNEL_STACK_PADDING.  This bug didn't matter because the
idle threads never enter user mode.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Reviewed-by: Borislav Petkov <bp@suse.de>
Cc: Borislav Petkov <bpetkov@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/e5e370a7e6e4fddd1c4e4cf619765d96bb874b21.1509609304.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Borislav Petkov <bp@suse.de>
---
 arch/x86/kernel/smpboot.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -959,8 +959,7 @@ void common_cpu_up(unsigned int cpu, str
 #ifdef CONFIG_X86_32
 	/* Stack for startup_32 can be just as for start_secondary onwards */
 	irq_ctx_init(cpu);
-	per_cpu(cpu_current_top_of_stack, cpu) =
-		(unsigned long)task_stack_page(idle) + THREAD_SIZE;
+	per_cpu(cpu_current_top_of_stack, cpu) = task_top_of_stack(idle);
 #else
 	initial_gs = per_cpu_offset(cpu);
 #endif