linux-kernel - Re: [PATCH 2/3 v3] x86/kexec: Set the C-bit in the identity map page table when SEV is active

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Date:   Wed, 15 May 2019 15:30:06 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Lianbo Jiang <lijiang@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
        tglx@...utronix.de, mingo@...hat.com, akpm@...ux-foundation.org,
        x86@...nel.org, hpa@...or.com, dyoung@...hat.com, bhe@...hat.com,
        Thomas.Lendacky@....com, brijesh.singh@....com
Subject: Re: [PATCH 2/3 v3] x86/kexec: Set the C-bit in the identity map page
 table when SEV is active

On Tue, Apr 30, 2019 at 03:44:20PM +0800, Lianbo Jiang wrote:
> When SEV is active, the second kernel image is loaded into the
> encrypted memory. Lets make sure that when kexec builds the
> identity mapping page table it adds the memory encryption mask(C-bit).
> 
> Co-developed-by: Brijesh Singh <brijesh.singh@....com>
> Signed-off-by: Brijesh Singh <brijesh.singh@....com>
> Signed-off-by: Lianbo Jiang <lijiang@...hat.com>
> ---
>  arch/x86/kernel/machine_kexec_64.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
> index f60611531d17..11fe352f7344 100644
> --- a/arch/x86/kernel/machine_kexec_64.c
> +++ b/arch/x86/kernel/machine_kexec_64.c
> @@ -56,6 +56,7 @@ static int init_transition_pgtable(struct kimage *image, pgd_t *pgd)
>  	pte_t *pte;
>  	unsigned long vaddr, paddr;
>  	int result = -ENOMEM;
> +	pgprot_t prot = PAGE_KERNEL_EXEC_NOENC;
>  
>  	vaddr = (unsigned long)relocate_kernel;
>  	paddr = __pa(page_address(image->control_code_page)+PAGE_SIZE);
> @@ -92,7 +93,11 @@ static int init_transition_pgtable(struct kimage *image, pgd_t *pgd)
>  		set_pmd(pmd, __pmd(__pa(pte) | _KERNPG_TABLE));
>  	}
>  	pte = pte_offset_kernel(pmd, vaddr);
> -	set_pte(pte, pfn_pte(paddr >> PAGE_SHIFT, PAGE_KERNEL_EXEC_NOENC));
> +
> +	if (sev_active())
> +		prot = PAGE_KERNEL_EXEC;
> +
> +	set_pte(pte, pfn_pte(paddr >> PAGE_SHIFT, prot));
>  	return 0;
>  err:
>  	return result;
> @@ -129,6 +134,11 @@ static int init_pgtable(struct kimage *image, unsigned long start_pgtable)
>  	level4p = (pgd_t *)__va(start_pgtable);
>  	clear_page(level4p);
>  
> +	if (sev_active()) {
> +		info.page_flag |= _PAGE_ENC;
> +		info.kernpg_flag = _KERNPG_TABLE;

kernpg_flag above is initialized to _KERNPG_TABLE_NOENC so you can do here

		info.kernpg_flag |= _PAGE_ENC;

too, to make it even more clear what this does, right?

IOW:

diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
index 783ce5184405..16c37fe489bc 100644
--- a/arch/x86/kernel/machine_kexec_64.c
+++ b/arch/x86/kernel/machine_kexec_64.c
@@ -135,8 +135,8 @@ static int init_pgtable(struct kimage *image, unsigned long start_pgtable)
        clear_page(level4p);
 
        if (sev_active()) {
-               info.page_flag |= _PAGE_ENC;
-               info.kernpg_flag = _KERNPG_TABLE;
+               info.page_flag   |= _PAGE_ENC;
+               info.kernpg_flag |= _PAGE_ENC;
        }
 
        if (direct_gbpages)


-- 
Regards/Gruss,
    Boris.

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