linux-hardening - Re: [PATCH v1 3/9] virt: Implement Heki common code

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Date:   Mon, 8 May 2023 17:29:41 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     Mickaël Salaün <mic@...ikod.net>
Cc:     Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H . Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Alexander Graf <graf@...zon.com>,
        Forrest Yuan Yu <yuanyu@...gle.com>,
        James Morris <jamorris@...ux.microsoft.com>,
        John Andersen <john.s.andersen@...el.com>,
        Liran Alon <liran.alon@...cle.com>,
        "Madhavan T . Venkataraman" <madvenka@...ux.microsoft.com>,
        Marian Rotariu <marian.c.rotariu@...il.com>,
        Mihai Donțu <mdontu@...defender.com>,
        Nicușor Cîțu <nicu.citu@...oud.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Thara Gopinath <tgopinath@...rosoft.com>,
        Will Deacon <will@...nel.org>,
        Zahra Tarkhani <ztarkhani@...rosoft.com>,
        Ștefan Șicleru <ssicleru@...defender.com>,
        dev@...ts.cloudhypervisor.org, kvm@...r.kernel.org,
        linux-hardening@...r.kernel.org, linux-hyperv@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org, qemu-devel@...gnu.org,
        virtualization@...ts.linux-foundation.org, x86@...nel.org,
        xen-devel@...ts.xenproject.org, Wei Liu <wei.liu@...nel.org>
Subject: Re: [PATCH v1 3/9] virt: Implement Heki common code

On Fri, May 05, 2023 at 05:20:40PM +0200, Mickaël Salaün wrote:
> From: Madhavan T. Venkataraman <madvenka@...ux.microsoft.com>
> 
> Hypervisor Enforced Kernel Integrity (Heki) is a feature that will use
> the hypervisor to enhance guest virtual machine security.
> 
> Configuration
> =============
> 
> Define the config variables for the feature. This feature depends on
> support from the architecture as well as the hypervisor.
> 
> Enabling HEKI
> =============
> 
> Define a kernel command line parameter "heki" to turn the feature on or
> off. By default, Heki is on.

For such a newfangled feature can we have it off by default? Especially
when there are unsolved issues around dynamically loaded code.

> 
[...]
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 3604074a878b..5cf5a7a97811 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -297,6 +297,7 @@ config X86
>  	select FUNCTION_ALIGNMENT_4B
>  	imply IMA_SECURE_AND_OR_TRUSTED_BOOT    if EFI
>  	select HAVE_DYNAMIC_FTRACE_NO_PATCHABLE
> +	select ARCH_SUPPORTS_HEKI		if X86_64

Why is there a restriction on X86_64?

>  
>  config INSTRUCTION_DECODER
>  	def_bool y
> diff --git a/arch/x86/include/asm/sections.h b/arch/x86/include/asm/sections.h
> index a6e8373a5170..42ef1e33b8a5 100644
> --- a/arch/x86/include/asm/sections.h
> +++ b/arch/x86/include/asm/sections.h
[...]
>  
> +#ifdef CONFIG_HEKI
> +
> +/*
> + * Gather all of the statically defined sections so heki_late_init() can
> + * protect these sections in the host page table.
> + *
> + * The sections are defined under "SECTIONS" in vmlinux.lds.S
> + * Keep this array in sync with SECTIONS.
> + */

This seems a bit fragile, because it requires constant attention from
people who care about this functionality. Can this table be
automatically generated?

Thanks,
Wei.

> +struct heki_va_range __initdata heki_va_ranges[] = {
> +	{
> +		.va_start = _stext,
> +		.va_end = _etext,
> +		.attributes = HEKI_ATTR_MEM_NOWRITE | HEKI_ATTR_MEM_EXEC,
> +	},
> +	{
> +		.va_start = __start_rodata,
> +		.va_end = __end_rodata,
> +		.attributes = HEKI_ATTR_MEM_NOWRITE,
> +	},
> +#ifdef CONFIG_UNWINDER_ORC
> +	{
> +		.va_start = __start_orc_unwind_ip,
> +		.va_end = __stop_orc_unwind_ip,
> +		.attributes = HEKI_ATTR_MEM_NOWRITE,
> +	},
> +	{
> +		.va_start = __start_orc_unwind,
> +		.va_end = __stop_orc_unwind,
> +		.attributes = HEKI_ATTR_MEM_NOWRITE,
> +	},
> +	{
> +		.va_start = orc_lookup,
> +		.va_end = orc_lookup_end,
> +		.attributes = HEKI_ATTR_MEM_NOWRITE,
> +	},
> +#endif /* CONFIG_UNWINDER_ORC */
> +};
> +