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x86/cpu: Call verify_cpu() after having entered long mode too

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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: "H. Peter Anvin" <hpa@zytor.com>
Reported-and-tested-by: Bastien Nocera <bugzilla@hadess.net>
Signed-off-by: Borislav 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: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Borislav Petkov 2015-11-05 16:57:56 +01:00 committed by Thomas Gleixner
parent 68accac392
commit 04633df0c4
2 changed files with 15 additions and 5 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

8
arch/x86/kernel/head_64.S
View file

@ -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

12
arch/x86/kernel/verify_cpu.S
View file

@ -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