linux-kernel - Re: [PATCH v1 3/3] x86/mm: Encrypt the initrd earlier for BSP microcode update

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Date:   Thu, 21 Dec 2017 15:49:25 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     x86@...nel.org, Brijesh Singh <brijesh.singh@....com>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v1 3/3] x86/mm: Encrypt the initrd earlier for BSP
 microcode update

On Thu, Dec 07, 2017 at 05:34:10PM -0600, Tom Lendacky wrote:
> Currently the BSP microcode update code examines the initrd very early
> in the boot process.  If SME is active, the initrd is treated as being
> encrypted but it has not been encrypted (in place) yet.  Update the
> early boot code that encrypts the kernel to also encrypt the initrd so
> that early BSP microcode updates work.

...

> diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
> index 1f0efb8..60df247 100644
> --- a/arch/x86/mm/mem_encrypt.c
> +++ b/arch/x86/mm/mem_encrypt.c
> @@ -731,11 +731,12 @@ static unsigned long __init sme_pgtable_calc(unsigned long len)
>  	return total;
>  }
>  
> -void __init sme_encrypt_kernel(void)
> +void __init sme_encrypt_kernel(struct boot_params *bp)
>  {
>  	unsigned long workarea_start, workarea_end, workarea_len;
>  	unsigned long execute_start, execute_end, execute_len;
>  	unsigned long kernel_start, kernel_end, kernel_len;
> +	unsigned long initrd_start, initrd_end, initrd_len;
>  	unsigned long pgtable_area_len;
>  	unsigned long decrypted_base;
>  	pgd_t *pgd;
> @@ -744,14 +745,15 @@ void __init sme_encrypt_kernel(void)
>  		return;
>  
>  	/*
> -	 * Prepare for encrypting the kernel by building new pagetables with
> -	 * the necessary attributes needed to encrypt the kernel in place.
> +	 * Prepare for encrypting the kernel and initrd by building new
> +	 * pagetables with the necessary attributes needed to encrypt the
> +	 * kernel in place.
>  	 *
>  	 *   One range of virtual addresses will map the memory occupied
> -	 *   by the kernel as encrypted.
> +	 *   by the kernel and initrd as encrypted.
>  	 *
>  	 *   Another range of virtual addresses will map the memory occupied
> -	 *   by the kernel as decrypted and write-protected.
> +	 *   by the kernel and initrd as decrypted and write-protected.
>  	 *
>  	 *     The use of write-protect attribute will prevent any of the
>  	 *     memory from being cached.
> @@ -762,6 +764,20 @@ void __init sme_encrypt_kernel(void)
>  	kernel_end = ALIGN(__pa_symbol(_end), PMD_PAGE_SIZE);
>  	kernel_len = kernel_end - kernel_start;
>  
> +	initrd_start = 0;
> +	initrd_end = 0;
> +	initrd_len = 0;
> +#ifdef CONFIG_BLK_DEV_INITRD
> +	initrd_len = (unsigned long)bp->hdr.ramdisk_size |
> +		     ((unsigned long)bp->ext_ramdisk_size << 32);
> +	if (initrd_len) {
> +		initrd_start = (unsigned long)bp->hdr.ramdisk_image |
> +			       ((unsigned long)bp->ext_ramdisk_image << 32);
> +		initrd_end = PAGE_ALIGN(initrd_start + initrd_len);
> +		initrd_len = initrd_end - initrd_start;
> +	}
> +#endif

In a prepatch, pls make get_ramdisk_image() and get_ramdisk_size() from
arch/x86/kernel/setup.c accessible to this code too. Also, add dummies
for the !CONFIG_BLK_DEV_INITRD case so that you can simply call them
here, regardless of the CONFIG_BLK_DEV_INITRD setting.

Then you won't need boot_params ptr either and that would simplify the
diff a bit.

Thx.

-- 
Regards/Gruss,
    Boris.

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