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Message-ID: <13174f0e-801c-bdac-5df9-484435de1f8e@redhat.com>
Date: Mon, 19 Jun 2023 14:12:18 +0200
From: David Hildenbrand <david@...hat.com>
To: Kai Huang <kai.huang@...el.com>, linux-kernel@...r.kernel.org,
kvm@...r.kernel.org
Cc: linux-mm@...ck.org, dave.hansen@...el.com,
kirill.shutemov@...ux.intel.com, tony.luck@...el.com,
peterz@...radead.org, tglx@...utronix.de, seanjc@...gle.com,
pbonzini@...hat.com, dan.j.williams@...el.com,
rafael.j.wysocki@...el.com, ying.huang@...el.com,
reinette.chatre@...el.com, len.brown@...el.com, ak@...ux.intel.com,
isaku.yamahata@...el.com, chao.gao@...el.com,
sathyanarayanan.kuppuswamy@...ux.intel.com, bagasdotme@...il.com,
sagis@...gle.com, imammedo@...hat.com
Subject: Re: [PATCH v11 02/20] x86/virt/tdx: Detect TDX during kernel boot
On 04.06.23 16:27, Kai Huang wrote:
> Intel Trust Domain Extensions (TDX) protects guest VMs from malicious
> host and certain physical attacks. A CPU-attested software module
> called 'the TDX module' runs inside a new isolated memory range as a
> trusted hypervisor to manage and run protected VMs.
>
> Pre-TDX Intel hardware has support for a memory encryption architecture
> called MKTME. The memory encryption hardware underpinning MKTME is also
> used for Intel TDX. TDX ends up "stealing" some of the physical address
> space from the MKTME architecture for crypto-protection to VMs. The
> BIOS is responsible for partitioning the "KeyID" space between legacy
> MKTME and TDX. The KeyIDs reserved for TDX are called 'TDX private
> KeyIDs' or 'TDX KeyIDs' for short.
>
> TDX doesn't trust the BIOS. During machine boot, TDX verifies the TDX
> private KeyIDs are consistently and correctly programmed by the BIOS
> across all CPU packages before it enables TDX on any CPU core. A valid
> TDX private KeyID range on BSP indicates TDX has been enabled by the
> BIOS, otherwise the BIOS is buggy.
>
> The TDX module is expected to be loaded by the BIOS when it enables TDX,
> but the kernel needs to properly initialize it before it can be used to
> create and run any TDX guests. The TDX module will be initialized by
> the KVM subsystem when KVM wants to use TDX.
>
> Add a new early_initcall(tdx_init) to detect the TDX by detecting TDX
> private KeyIDs. Also add a function to report whether TDX is enabled by
> the BIOS. Similar to AMD SME, kexec() will use it to determine whether
> cache flush is needed.
>
> The TDX module itself requires one TDX KeyID as the 'TDX global KeyID'
> to protect its metadata. Each TDX guest also needs a TDX KeyID for its
> own protection. Just use the first TDX KeyID as the global KeyID and
> leave the rest for TDX guests. If no TDX KeyID is left for TDX guests,
> disable TDX as initializing the TDX module alone is useless.
>
> To start to support TDX, create a new arch/x86/virt/vmx/tdx/tdx.c for
> TDX host kernel support. Add a new Kconfig option CONFIG_INTEL_TDX_HOST
> to opt-in TDX host kernel support (to distinguish with TDX guest kernel
> support). So far only KVM uses TDX. Make the new config option depend
> on KVM_INTEL.
>
> Signed-off-by: Kai Huang <kai.huang@...el.com>
> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> ---
>
> v10 -> v11 (David):
> - "host kernel" -> "the host kernel"
> - "protected VM" -> "confidential VM".
> - Moved setting tdx_global_keyid to the end of tdx_init().
>
> v9 -> v10:
> - No change.
>
> v8 -> v9:
> - Moved MSR macro from local tdx.h to <asm/msr-index.h> (Dave).
> - Moved reserving the TDX global KeyID from later patch to here.
> - Changed 'tdx_keyid_start' and 'nr_tdx_keyids' to
> 'tdx_guest_keyid_start' and 'tdx_nr_guest_keyids' to represent KeyIDs
> can be used by guest. (Dave)
> - Slight changelog update according to above changes.
>
> v7 -> v8: (address Dave's comments)
> - Improved changelog:
> - "KVM user" -> "The TDX module will be initialized by KVM when ..."
> - Changed "tdx_int" part to "Just say what this patch is doing"
> - Fixed the last sentence of "kexec()" paragraph
> - detect_tdx() -> record_keyid_partitioning()
> - Improved how to calculate tdx_keyid_start.
> - tdx_keyid_num -> nr_tdx_keyids.
> - Improved dmesg printing.
> - Add comment to clear_tdx().
>
> v6 -> v7:
> - No change.
>
> v5 -> v6:
> - Removed SEAMRR detection to make code simpler.
> - Removed the 'default N' in the KVM_TDX_HOST Kconfig (Kirill).
> - Changed to use 'obj-y' in arch/x86/virt/vmx/tdx/Makefile (Kirill).
>
>
> ---
> arch/x86/Kconfig | 12 +++++
> arch/x86/Makefile | 2 +
> arch/x86/include/asm/msr-index.h | 3 ++
> arch/x86/include/asm/tdx.h | 7 +++
> arch/x86/virt/Makefile | 2 +
> arch/x86/virt/vmx/Makefile | 2 +
> arch/x86/virt/vmx/tdx/Makefile | 2 +
> arch/x86/virt/vmx/tdx/tdx.c | 92 ++++++++++++++++++++++++++++++++
> 8 files changed, 122 insertions(+)
> create mode 100644 arch/x86/virt/Makefile
> create mode 100644 arch/x86/virt/vmx/Makefile
> create mode 100644 arch/x86/virt/vmx/tdx/Makefile
> create mode 100644 arch/x86/virt/vmx/tdx/tdx.c
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 53bab123a8ee..191587f75810 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1952,6 +1952,18 @@ config X86_SGX
>
> If unsure, say N.
>
> +config INTEL_TDX_HOST
> + bool "Intel Trust Domain Extensions (TDX) host support"
> + depends on CPU_SUP_INTEL
> + depends on X86_64
> + depends on KVM_INTEL
> + help
> + Intel Trust Domain Extensions (TDX) protects guest VMs from malicious
> + host and certain physical attacks. This option enables necessary TDX
> + support in the host kernel to run confidential VMs.
> +
> + If unsure, say N.
> +
> config EFI
> bool "EFI runtime service support"
> depends on ACPI
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index b39975977c03..ec0e71d8fa30 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -252,6 +252,8 @@ archheaders:
>
> libs-y += arch/x86/lib/
>
> +core-y += arch/x86/virt/
> +
> # drivers-y are linked after core-y
> drivers-$(CONFIG_MATH_EMULATION) += arch/x86/math-emu/
> drivers-$(CONFIG_PCI) += arch/x86/pci/
> diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
> index 3aedae61af4f..6d8f15b1552c 100644
> --- a/arch/x86/include/asm/msr-index.h
> +++ b/arch/x86/include/asm/msr-index.h
> @@ -523,6 +523,9 @@
> #define MSR_RELOAD_PMC0 0x000014c1
> #define MSR_RELOAD_FIXED_CTR0 0x00001309
>
> +/* KeyID partitioning between MKTME and TDX */
> +#define MSR_IA32_MKTME_KEYID_PARTITIONING 0x00000087
> +
> /*
> * AMD64 MSRs. Not complete. See the architecture manual for a more
> * complete list.
> diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
> index 25fd6070dc0b..4dfe2e794411 100644
> --- a/arch/x86/include/asm/tdx.h
> +++ b/arch/x86/include/asm/tdx.h
> @@ -94,5 +94,12 @@ static inline long tdx_kvm_hypercall(unsigned int nr, unsigned long p1,
> return -ENODEV;
> }
> #endif /* CONFIG_INTEL_TDX_GUEST && CONFIG_KVM_GUEST */
> +
> +#ifdef CONFIG_INTEL_TDX_HOST
> +bool platform_tdx_enabled(void);
> +#else /* !CONFIG_INTEL_TDX_HOST */
> +static inline bool platform_tdx_enabled(void) { return false; }
> +#endif /* CONFIG_INTEL_TDX_HOST */
> +
> #endif /* !__ASSEMBLY__ */
> #endif /* _ASM_X86_TDX_H */
> diff --git a/arch/x86/virt/Makefile b/arch/x86/virt/Makefile
> new file mode 100644
> index 000000000000..1e36502cd738
> --- /dev/null
> +++ b/arch/x86/virt/Makefile
> @@ -0,0 +1,2 @@
> +# SPDX-License-Identifier: GPL-2.0-only
> +obj-y += vmx/
> diff --git a/arch/x86/virt/vmx/Makefile b/arch/x86/virt/vmx/Makefile
> new file mode 100644
> index 000000000000..feebda21d793
> --- /dev/null
> +++ b/arch/x86/virt/vmx/Makefile
> @@ -0,0 +1,2 @@
> +# SPDX-License-Identifier: GPL-2.0-only
> +obj-$(CONFIG_INTEL_TDX_HOST) += tdx/
> diff --git a/arch/x86/virt/vmx/tdx/Makefile b/arch/x86/virt/vmx/tdx/Makefile
> new file mode 100644
> index 000000000000..93ca8b73e1f1
> --- /dev/null
> +++ b/arch/x86/virt/vmx/tdx/Makefile
> @@ -0,0 +1,2 @@
> +# SPDX-License-Identifier: GPL-2.0-only
> +obj-y += tdx.o
> diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> new file mode 100644
> index 000000000000..2d91e7120c90
> --- /dev/null
> +++ b/arch/x86/virt/vmx/tdx/tdx.c
> @@ -0,0 +1,92 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright(c) 2023 Intel Corporation.
> + *
> + * Intel Trusted Domain Extensions (TDX) support
> + */
> +
> +#define pr_fmt(fmt) "tdx: " fmt
> +
> +#include <linux/types.h>
> +#include <linux/cache.h>
> +#include <linux/init.h>
> +#include <linux/errno.h>
> +#include <linux/printk.h>
> +#include <asm/msr-index.h>
> +#include <asm/msr.h>
> +#include <asm/tdx.h>
> +
> +static u32 tdx_global_keyid __ro_after_init;
> +static u32 tdx_guest_keyid_start __ro_after_init;
> +static u32 tdx_nr_guest_keyids __ro_after_init;
> +
> +static int __init record_keyid_partitioning(u32 *tdx_keyid_start,
> + u32 *nr_tdx_keyids)
> +{
> + u32 _nr_mktme_keyids, _tdx_keyid_start, _nr_tdx_keyids;
> + int ret;
> +
> + /*
> + * IA32_MKTME_KEYID_PARTIONING:
> + * Bit [31:0]: Number of MKTME KeyIDs.
> + * Bit [63:32]: Number of TDX private KeyIDs.
> + */
> + ret = rdmsr_safe(MSR_IA32_MKTME_KEYID_PARTITIONING, &_nr_mktme_keyids,
> + &_nr_tdx_keyids);
> + if (ret)
> + return -ENODEV;
> +
> + if (!_nr_tdx_keyids)
> + return -ENODEV;
> +
> + /* TDX KeyIDs start after the last MKTME KeyID. */
> + _tdx_keyid_start = _nr_mktme_keyids + 1;
> +
> + *tdx_keyid_start = _tdx_keyid_start;
> + *nr_tdx_keyids = _nr_tdx_keyids;
> +
> + return 0;
> +}
> +
> +static int __init tdx_init(void)
> +{
> + u32 tdx_keyid_start, nr_tdx_keyids;
> + int err;
> +
> + err = record_keyid_partitioning(&tdx_keyid_start, &nr_tdx_keyids);
> + if (err)
> + return err;
> +
> + pr_info("BIOS enabled: private KeyID range [%u, %u)\n",
> + tdx_keyid_start, tdx_keyid_start + nr_tdx_keyids);
> +
> + /*
> + * The TDX module itself requires one 'global KeyID' to protect
> + * its metadata. If there's only one TDX KeyID, there won't be
> + * any left for TDX guests thus there's no point to enable TDX
> + * at all.
> + */
> + if (nr_tdx_keyids < 2) {
> + pr_info("initialization failed: too few private KeyIDs available.\n");
> + goto no_tdx;
> + }
> +
> + /*
> + * Just use the first TDX KeyID as the 'global KeyID' and
> + * leave the rest for TDX guests.
> + */
> + tdx_global_keyid = tdx_keyid_start;
> + tdx_guest_keyid_start = ++tdx_keyid_start;
> + tdx_nr_guest_keyids = --nr_tdx_keyids;
tdx_guest_keyid_start = tdx_keyid_start + 1;
tdx_nr_guest_keyids = nr_tdx_keyids - 1;
Easier to get, because the modified values are unused.
I'd probably avoid the "tdx" terminology in the local variables
("keid_start", "nr_keyids") to give a better hint what the global
variables are (tdx_*), but just a personal preference.
Apart from that,
Reviewed-by: David Hildenbrand <david@...hat.com>
--
Cheers,
David / dhildenb
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