linux-kernel - Re: General protection fault in `switch_mm_irqs

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Message-ID: <e45c8578-37e8-0aee-b235-d4d9bcedc8ee@molgen.mpg.de>
Date:   Mon, 14 Jan 2019 18:09:35 +0100
From:   Paul Menzel <pmenzel@...gen.mpg.de>
To:     Thomas Lendacky <Thomas.Lendacky@....com>,
        Borislav Petkov <bp@...en8.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Jiri Kosina <jikos@...nel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>
Subject: Re: General protection fault in `switch_mm_irqs_off()`

Dear Thomas,


Thank you for checking this, and coming back with the results so quickly.

On 01/14/19 18:00, Lendacky, Thomas wrote:
> On 1/10/19 12:34 PM, Lendacky, Thomas wrote:
>> On 1/10/19 10:49 AM, Paul Menzel wrote:
>>> Dear Boris, dear Thomas,
>>>
>>>
>>> On 01/10/19 17:00, Borislav Petkov wrote:
>>>> On Thu, Jan 10, 2019 at 02:57:40PM +0100, Paul Menzel wrote:
>>>>> Thank you very much. Indeed, the machine does not crash. I used Linus’
>>>>> master branch for testing, and applied your patch on top. Please find
>>>>> the full log attached.
>>>>
>>>>> 80.649: [    3.197107] Spectre V2 : spectre_v2_user_select_mitigation: set X86_FEATURE_USE_IBPB
>>>>
>>>> This is amazing.
>>>>
>>>> Ok, next diff, same exercise. Thx.> 
>>>> ---
>>>> diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
>>>> index dad12b767ba0..528ef8336f5f 100644
>>>> --- a/arch/x86/include/asm/nospec-branch.h
>>>> +++ b/arch/x86/include/asm/nospec-branch.h
>>>> @@ -284,6 +284,12 @@ static inline void indirect_branch_prediction_barrier(void)
>>>>  {
>>>>  	u64 val = PRED_CMD_IBPB;
>>>>  
>>>> +	if (WARN_ON(boot_cpu_has(X86_FEATURE_USE_IBPB))) {
>>>> +		pr_info("%s: c: %px, array: 0x%x\n",
>>>> +			__func__, &boot_cpu_data, boot_cpu_data.x86_capability[7]);
>>>> +		return;
>>>> +	}
>>>> +
>>>>  	alternative_msr_write(MSR_IA32_PRED_CMD, val, X86_FEATURE_USE_IBPB);
>>>>  }
>>>>  
>>>> diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
>>>> index 8654b8b0c848..e818e5abe611 100644
>>>> --- a/arch/x86/kernel/cpu/bugs.c
>>>> +++ b/arch/x86/kernel/cpu/bugs.c
>>>> @@ -371,6 +371,9 @@ spectre_v2_user_select_mitigation(enum spectre_v2_mitigation_cmd v2_cmd)
>>>>  	if (boot_cpu_has(X86_FEATURE_IBPB)) {
>>>>  		setup_force_cpu_cap(X86_FEATURE_USE_IBPB);
>>>>  
>>>> +		pr_err("%s: set X86_FEATURE_USE_IBPB, c: %px, array: 0x%x\n",
>>>> +			__func__, &boot_cpu_data, boot_cpu_data.x86_capability[7]);
>>>> +
>>>>  		switch (cmd) {
>>>>  		case SPECTRE_V2_USER_CMD_FORCE:
>>>>  		case SPECTRE_V2_USER_CMD_PRCTL_IBPB:
>>>> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
>>>> index cb28e98a0659..8566737fa500 100644
>>>> --- a/arch/x86/kernel/cpu/common.c
>>>> +++ b/arch/x86/kernel/cpu/common.c
>>>> @@ -765,6 +765,9 @@ static void apply_forced_caps(struct cpuinfo_x86 *c)
>>>>  		c->x86_capability[i] &= ~cpu_caps_cleared[i];
>>>>  		c->x86_capability[i] |= cpu_caps_set[i];
>>>>  	}
>>>> +
>>>> +	if (c == &boot_cpu_data)
>>>> +		pr_info("%s: c: %px, array: 0x%x\n", __func__, c, c->x86_capability[7]);
>>>>  }
>>>>  
>>>>  static void init_speculation_control(struct cpuinfo_x86 *c)
>>>> @@ -778,6 +781,10 @@ static void init_speculation_control(struct cpuinfo_x86 *c)
>>>>  	if (cpu_has(c, X86_FEATURE_SPEC_CTRL)) {
>>>>  		set_cpu_cap(c, X86_FEATURE_IBRS);
>>>>  		set_cpu_cap(c, X86_FEATURE_IBPB);
>>>> +
>>>> +		pr_info("%s: X86_FEATURE_SPEC_CTRL: c: %px, array: 0x%x, CPUID: 0x%x\n",
>>>> +			__func__, c, c->x86_capability[7], cpuid_edx(7));
>>>> +
>>>>  		set_cpu_cap(c, X86_FEATURE_MSR_SPEC_CTRL);
>>>>  	}
>>>>  
>>>> @@ -793,9 +800,13 @@ static void init_speculation_control(struct cpuinfo_x86 *c)
>>>>  		set_cpu_cap(c, X86_FEATURE_MSR_SPEC_CTRL);
>>>>  	}
>>>>  
>>>> -	if (cpu_has(c, X86_FEATURE_AMD_IBPB))
>>>> +	if (cpu_has(c, X86_FEATURE_AMD_IBPB)) {
>>>>  		set_cpu_cap(c, X86_FEATURE_IBPB);
>>>>  
>>>> +		pr_info("%s: X86_FEATURE_AMD_IBPB: c: %px, array: 0x%x, CPUID: 0x%x\n",
>>>> +			__func__, c, c->x86_capability[7], cpuid_ebx(0x80000008));
>>>> +	}
>>>> +
>>>>  	if (cpu_has(c, X86_FEATURE_AMD_STIBP)) {
>>>>  		set_cpu_cap(c, X86_FEATURE_STIBP);
>>>>  		set_cpu_cap(c, X86_FEATURE_MSR_SPEC_CTRL);
>>>
>>> Please find the logs attached.
>>
>> Ah, so the CPUID value is showing X86_FEATURE_AMD_IBPB (not sure why the
>> cpuid command was showing a value of zero for EBX in your previous email).
>> Let me see what I can find out about this processor/firmware relation. I
>> wouldn't expect to see the #GP given that the firmware says IBPB is
>> supported.
> 
> I'm not able to reproduce this issue on my family 21, model 1, stepping 2
> processor (AMD Opteron(TM) Processor 6274) as I am able to successfully
> write to the PRED_CMD MSR.

It’s not exactly the same processor, but I guess the same family should be
good enough. What board do you have? Do you have two sockets, and both
populated?

Here is an Asus KGPE-D16 with two AMD Opterons put in.

Lastly, my microcode updates are applied in firmware, and not by GNU/Linux.

> Let's check the firmware file that you're loading. The one I'm using is:
> 
> $ sha1sum /lib/firmware/amd-ucode/microcode_amd_fam15h.bin 
> 90896256951d8edf7baf8181ae11e2dc618a5171  /lib/firmware/amd-ucode/microcode_amd_fam15h.bin
> 
> Does that match what you have?

Yes, that matches exactly.

    90896256951d8edf7baf8181ae11e2dc618a5171  3rdparty/blobs/cpu/amd/family_15h/microcode_amd_fam15h.bin


Kind regards,

Paul


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