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

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Date:   Thu, 10 Jan 2019 17:49:23 +0100
From:   Paul Menzel <pmenzel@...gen.mpg.de>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Thomas Lendacky <Thomas.Lendacky@....com>,
        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 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.


Kind regards,

Paul

View attachment "coreboot-ucode-updates-0x0600063e-linux-5.0-rc1+-more-debug-from-boris-spectre_v2_user-auto.log" of type "text/x-log" (131684 bytes)

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