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Commit 04633df0 authored by Borislav Petkov's avatar Borislav Petkov Committed by Thomas Gleixner
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x86/cpu: Call verify_cpu() after having entered long mode too 

When we get loaded by a 64-bit bootloader, kernel entry point is
startup_64 in head_64.S. We don't trust any and all bootloaders because
some will fiddle with CPU configuration so we go ahead and massage each
CPU into sanity again.

For example, some dell BIOSes have this XD disable feature which set
IA32_MISC_ENABLE[34] and disable NX. This might be some dumb workaround
for other OSes but Linux sure doesn't need it.

A similar thing is present in the Surface 3 firmware - see
https://bugzilla.kernel.org/show_bug.cgi?id=106051

 - which sets this bit
only on the BSP:

  # rdmsr -a 0x1a0
  400850089
  850089
  850089
  850089

I know, right?!

There's not even an off switch in there.

So fix all those cases by sanitizing the 64-bit entry point too. For
that, make verify_cpu() callable in 64-bit mode also.

Requested-and-debugged-by: default avatar"H. Peter Anvin" <hpa@zytor.com>
Reported-and-tested-by: default avatarBastien Nocera <bugzilla@hadess.net>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/1446739076-21303-1-git-send-email-bp@alien8.de


Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 68accac3

arch/x86/kernel/head_64.S

+8 −0
Original line number Diff line number Diff line
@@ -65,6 +65,9 @@ startup_64: 
	 * tables and then reload them.

	 */



	/* Sanitize CPU configuration */

	call verify_cpu



	/*

	 * Compute the delta between the address I am compiled to run at and the

	 * address I am actually running at.
@@ -174,6 +177,9 @@ ENTRY(secondary_startup_64) 
	 * after the boot processor executes this code.

	 */



	/* Sanitize CPU configuration */

	call verify_cpu



	movq	$(init_level4_pgt - __START_KERNEL_map), %rax

1:
@@ -288,6 +294,8 @@ ENTRY(secondary_startup_64) 
	pushq	%rax		# target address in negative space

	lretq



#include "verify_cpu.S"



#ifdef CONFIG_HOTPLUG_CPU

/*

 * Boot CPU0 entry point. It's called from play_dead(). Everything has been set

arch/x86/kernel/verify_cpu.S

+7 −5
Original line number Diff line number Diff line
@@ -34,10 +34,11 @@ 
#include <asm/msr-index.h>



verify_cpu:

	pushfl				# Save caller passed flags

	pushl	$0			# Kill any dangerous flags

	popfl

	pushf				# Save caller passed flags

	push	$0			# Kill any dangerous flags

	popf



#ifndef __x86_64__

	pushfl				# standard way to check for cpuid

	popl	%eax

	movl	%eax,%ebx
@@ -48,6 +49,7 @@ verify_cpu: 
	popl	%eax

	cmpl	%eax,%ebx

	jz	verify_cpu_no_longmode	# cpu has no cpuid

#endif



	movl	$0x0,%eax		# See if cpuid 1 is implemented

	cpuid
@@ -130,10 +132,10 @@ verify_cpu_sse_test: 
	jmp	verify_cpu_sse_test	# try again



verify_cpu_no_longmode:

	popfl				# Restore caller passed flags

	popf				# Restore caller passed flags

	movl $1,%eax

	ret

verify_cpu_sse_ok:

	popfl				# Restore caller passed flags

	popf				# Restore caller passed flags

	xorl %eax, %eax

	ret