From: Borislav Petkov <bp@xxxxxxx> 3.4.113-rc1 review patch. If anyone has any objections, please let me know. ------------------ 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> [lizf: Backported to 3.4: adjust context] Signed-off-by: Zefan Li <lizefan@xxxxxxxxxx> --- 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 40f4eb3..59d0eac 100644 --- a/arch/x86/kernel/head_64.S +++ b/arch/x86/kernel/head_64.S @@ -45,6 +45,9 @@ L3_START_KERNEL = pud_index(__START_KERNEL_map) .globl startup_64 startup_64: + /* Sanitize CPU configuration */ + call verify_cpu + /* * At this point the CPU runs in 64bit mode CS.L = 1 CS.D = 1, * and someone has loaded an identity mapped page table @@ -160,6 +163,9 @@ ENTRY(secondary_startup_64) * after the boot processor executes this code. */ + /* Sanitize CPU configuration */ + call verify_cpu + /* Enable PAE mode and PGE */ movl $(X86_CR4_PAE | X86_CR4_PGE), %eax movq %rax, %cr4 @@ -253,6 +259,8 @@ ENTRY(secondary_startup_64) pushq %rax # target address in negative space lretq +#include "verify_cpu.S" + /* SMP bootup changes these two */ __REFDATA .align 8 diff --git a/arch/x86/kernel/verify_cpu.S b/arch/x86/kernel/verify_cpu.S index b9242ba..4cf401f 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 -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html