Re: General protection fault in `switch_mm_irqs_off()`

Lendacky, Thomas
2019-01-10T18:34:16Z

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.

Thanks,
Tom

>
>
> Kind regards,
>
> Paul
>