Re: General protection fault in `switch_mm_irqs_off()`

Lendacky, Thomas
2019-01-14T17:00:50Z

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. 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?

Thanks,
Tom

> Thanks,
> Tom
>
>>
>>
>> Kind regards,
>>
>> Paul
>>