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authorBorislav Petkov <bp@suse.de>2015-11-05 16:57:56 +0100
committerThomas Gleixner <tglx@linutronix.de>2015-11-07 10:45:02 +0100
commit04633df0c43d710e5f696b06539c100898678235 (patch)
treef89040bf51f76c386da00dd8a18312c5bf959d70 /arch/x86/kernel/verify_cpu.S
parent68accac392d859d24adcf1be3a90e41f978bd54c (diff)
downloadlinux-04633df0c43d710e5f696b06539c100898678235.tar.bz2
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: "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>
Diffstat (limited to 'arch/x86/kernel/verify_cpu.S')
-rw-r--r--arch/x86/kernel/verify_cpu.S12
1 files changed, 7 insertions, 5 deletions
diff --git a/arch/x86/kernel/verify_cpu.S b/arch/x86/kernel/verify_cpu.S
index b9242bacbe59..4cf401f581e7 100644
--- 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