linux-kernel - Re: [PATCH v3 19/75] x86/boot/compressed/64: Add stage1 #VC handler

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Date:   Sat, 9 May 2020 11:05:48 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Joerg Roedel <joro@...tes.org>
Cc:     x86@...nel.org, hpa@...or.com, Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Hellstrom <thellstrom@...are.com>,
        Jiri Slaby <jslaby@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Juergen Gross <jgross@...e.com>,
        Kees Cook <keescook@...omium.org>,
        David Rientjes <rientjes@...gle.com>,
        Cfir Cohen <cfir@...gle.com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mike Stunes <mstunes@...are.com>,
        Joerg Roedel <jroedel@...e.de>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v3 19/75] x86/boot/compressed/64: Add stage1 #VC handler

On Tue, Apr 28, 2020 at 05:16:29PM +0200, Joerg Roedel wrote:
> From: Joerg Roedel <jroedel@...e.de>
> 
> Add the first handler for #VC exceptions. At stage 1 there is no GHCB
> yet becaue we might still be on the EFI page table and thus can't map

     "... because the kernel might still be running on the EFI page table... "

> memory unencrypted.
> 
> The stage 1 handler is limited to the MSR based protocol to talk to
> the hypervisor and can only support CPUID exit-codes, but that is
> enough to get to stage 2.
> 
> Signed-off-by: Joerg Roedel <jroedel@...e.de>
> ---
>  arch/x86/boot/compressed/Makefile          |  1 +
>  arch/x86/boot/compressed/idt_64.c          |  4 ++
>  arch/x86/boot/compressed/idt_handlers_64.S |  4 ++
>  arch/x86/boot/compressed/misc.h            |  1 +
>  arch/x86/boot/compressed/sev-es.c          | 45 +++++++++++++++
>  arch/x86/include/asm/msr-index.h           |  1 +
>  arch/x86/include/asm/sev-es.h              | 37 ++++++++++++
>  arch/x86/include/asm/trap_defs.h           |  1 +
>  arch/x86/kernel/sev-es-shared.c            | 65 ++++++++++++++++++++++
>  9 files changed, 159 insertions(+)
>  create mode 100644 arch/x86/boot/compressed/sev-es.c
>  create mode 100644 arch/x86/include/asm/sev-es.h
>  create mode 100644 arch/x86/kernel/sev-es-shared.c
> 
> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> index c6909d10a6b9..a7847a1ef63a 100644
> --- a/arch/x86/boot/compressed/Makefile
> +++ b/arch/x86/boot/compressed/Makefile
> @@ -85,6 +85,7 @@ ifdef CONFIG_X86_64
>  	vmlinux-objs-y += $(obj)/idt_64.o $(obj)/idt_handlers_64.o
>  	vmlinux-objs-y += $(obj)/mem_encrypt.o
>  	vmlinux-objs-y += $(obj)/pgtable_64.o
> +	vmlinux-objs-$(CONFIG_AMD_MEM_ENCRYPT) += $(obj)/sev-es.o
>  endif
>  
>  vmlinux-objs-$(CONFIG_ACPI) += $(obj)/acpi.o
> diff --git a/arch/x86/boot/compressed/idt_64.c b/arch/x86/boot/compressed/idt_64.c
> index 99cc78062684..f8295d68b3e1 100644
> --- a/arch/x86/boot/compressed/idt_64.c
> +++ b/arch/x86/boot/compressed/idt_64.c
> @@ -31,6 +31,10 @@ void load_stage1_idt(void)
>  {
>  	boot_idt_desc.address = (unsigned long)boot_idt;
>  
> +#ifdef CONFIG_AMD_MEM_ENCRYPT
> +	set_idt_entry(X86_TRAP_VC, boot_stage1_vc);
> +#endif

	if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT))

seems to work too and drops the ifdeffery ugliness.

...

> +void __init do_vc_no_ghcb(struct pt_regs *regs, unsigned long exit_code)
> +{
> +	unsigned int fn = lower_bits(regs->ax, 32);
> +	unsigned long val;
> +
> +	/* Only CPUID is supported via MSR protocol */
> +	if (exit_code != SVM_EXIT_CPUID)
> +		goto fail;
> +
> +	sev_es_wr_ghcb_msr(GHCB_CPUID_REQ(fn, GHCB_CPUID_REQ_EAX));
> +	VMGEXIT();
> +	val = sev_es_rd_ghcb_msr();
> +	if (GHCB_SEV_GHCB_RESP_CODE(val) != GHCB_SEV_CPUID_RESP)
> +		goto fail;
> +	regs->ax = val >> 32;
> +
> +	sev_es_wr_ghcb_msr(GHCB_CPUID_REQ(fn, GHCB_CPUID_REQ_EBX));
> +	VMGEXIT();
> +	val = sev_es_rd_ghcb_msr();
> +	if (GHCB_SEV_GHCB_RESP_CODE(val) != GHCB_SEV_CPUID_RESP)
> +		goto fail;
> +	regs->bx = val >> 32;
> +
> +	sev_es_wr_ghcb_msr(GHCB_CPUID_REQ(fn, GHCB_CPUID_REQ_ECX));
> +	VMGEXIT();
> +	val = sev_es_rd_ghcb_msr();
> +	if (GHCB_SEV_GHCB_RESP_CODE(val) != GHCB_SEV_CPUID_RESP)
> +		goto fail;
> +	regs->cx = val >> 32;
> +
> +	sev_es_wr_ghcb_msr(GHCB_CPUID_REQ(fn, GHCB_CPUID_REQ_EDX));
> +	VMGEXIT();
> +	val = sev_es_rd_ghcb_msr();
> +	if (GHCB_SEV_GHCB_RESP_CODE(val) != GHCB_SEV_CPUID_RESP)
> +		goto fail;
> +	regs->dx = val >> 32;

This could use a comment:

	/* Skip over the CPUID two-byte opcode */

or so.

-- 
Regards/Gruss,
    Boris.

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