Re: [v4.17-rcx] Lost IBPB, IBRS_FW support for spectre_v2 mitigation.

[Thomas Gleixner]

JÃrg,

On Mon, 30 Apr 2018, JÃrg Otte wrote:

> In v4.16 I already had support for BPB, IBRS_FW for spectre_v2 mitigation.
> But this went away in v17-rcx.
> 
> With 4.16 I have:
> jojo@fichte:~$ cd /sys/devices/system/cpu/vulnerabilities; grep ".*" *
> meltdown:Mitigation: PTI
> spectre_v1:Mitigation: __user pointer sanitization
> spectre_v2:Mitigation: Full generic retpoline, IBPB, IBRS_FW
> 
> With 4.17-rcx I have:
> meltdown:Mitigation: PTI
> spectre_v1:Mitigation: __user pointer sanitization
> spectre_v2:Mitigation: Full generic retpoline
> 
> Processor is
> vendor_id       : GenuineIntel
> cpu family      : 6
> model           : 60
> model name      : Intel(R) Core(TM) i5-4200M CPU @ 2.50GHz
> stepping        : 3
> microcode       : 0x24
> 
> 
> The problem goes away if I revert:
> d94a155 x86/cpu: Prevent cpuinfo_x86::x86_phys_bits adjustment corruption

Does the patch below fix the problem for you?

Thanks,

	tglx

8<------------------
Subject: x86/cpu: Restore CPUID_8000_0008_EBX reload
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Date: Mon, 30 Apr 2018 21:47:46 +0200

The recent commt which addresses the x86_phys_bits corruption with
encrypted memory on CPUID reload after a microcode update lost the reload
of CPUID_8000_0008_EBX as well.

As a consequence IBRS and IBRS_FW are not longer detected

Restore the behaviour by bringing the reload of CPUID_8000_0008_EBX back,.

Fixes: d94a155c59c9 ("x86/cpu: Prevent cpuinfo_x86::x86_phys_bits adjustment corruption")
Reported-by: JÃrg Otte <jrg.otte@xxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: kirill.shutemov@xxxxxxxxxxxxxxx
---
 arch/x86/kernel/cpu/common.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -848,6 +848,11 @@ void get_cpu_cap(struct cpuinfo_x86 *c)
 		c->x86_power = edx;
 	}
 
+	if (c->extended_cpuid_level >= 0x80000008) {
+		cpuid(0x80000008, &eax, &ebx, &ecx, &edx);
+		c->x86_capability[CPUID_8000_0008_EBX] = ebx;
+	}
+
 	if (c->extended_cpuid_level >= 0x8000000a)
 		c->x86_capability[CPUID_8000_000A_EDX] = cpuid_edx(0x8000000a);