From 04633df0c43d710e5f696b06539c100898678235 Mon Sep 17 00:00:00 2001 From: Borislav Petkov Date: Thu, 5 Nov 2015 16:57:56 +0100 Subject: [PATCH] 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" Reported-and-tested-by: Bastien Nocera Signed-off-by: Borislav Petkov Cc: Matt Fleming Cc: Peter Zijlstra 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 --- arch/x86/kernel/head_64.S | 8 ++++++++ arch/x86/kernel/verify_cpu.S | 12 +++++++----- 2 files changed, 15 insertions(+), 5 deletions(-) diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S index 1d40ca8a73f2..ffdc0e860390 100644 --- 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 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 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