This is a note to let you know that I've just added the patch titled
x86/cpu: Call verify_cpu() after having entered long mode too
to the 3.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-cpu-call-verify_cpu-after-having-entered-long-mode-too.patch
and it can be found in the queue-3.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 04633df0c43d710e5f696b06539c100898678235 Mon Sep 17 00:00:00 2001
From: Borislav Petkov <bp@xxxxxxx>
Date: Thu, 5 Nov 2015 16:57:56 +0100
Subject: x86/cpu: Call verify_cpu() after having entered long mode too
From: Borislav Petkov <bp@xxxxxxx>
commit 04633df0c43d710e5f696b06539c100898678235 upstream.
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@xxxxxxxxx>
Reported-and-tested-by: Bastien Nocera <bugzilla@xxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Cc: Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1446739076-21303-1-git-send-email-bp@xxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/head_64.S | 8 ++++++++
arch/x86/kernel/verify_cpu.S | 12 +++++++-----
2 files changed, 15 insertions(+), 5 deletions(-)
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -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
--- a/arch/x86/kernel/verify_cpu.S
+++ b/arch/x86/kernel/verify_cpu.S
@@ -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
Patches currently in stable-queue which might be from bp@xxxxxxx are
queue-3.10/x86-cpu-call-verify_cpu-after-having-entered-long-mode-too.patch
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