Re: [RFC PATCH v2 10/20] x86: Insure that memory areas are encrypted when possible

[Tom Lendacky <thomas.lendacky@amd.com>]

On 09/09/2016 10:53 AM, Borislav Petkov wrote:
> On Mon, Aug 22, 2016 at 05:37:23PM -0500, Tom Lendacky wrote:
>> Encrypt memory areas in place when possible (e.g. zero page, etc.) so
>> that special handling isn't needed afterwards.
>>
>> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
>> ---
>>  arch/x86/kernel/head64.c |   93 ++++++++++++++++++++++++++++++++++++++++++++--
>>  arch/x86/kernel/setup.c  |    8 ++++
>>  2 files changed, 96 insertions(+), 5 deletions(-)
> 
> ...
> 
>> +int __init early_make_pgtable(unsigned long address)
>> +{
>> +	unsigned long physaddr = address - __PAGE_OFFSET;
>> +	pmdval_t pmd;
>> +
>> +	pmd = (physaddr & PMD_MASK) + early_pmd_flags;
>> +
>> +	return __early_make_pgtable(address, pmd);
>> +}
>> +
>> +static void __init create_unencrypted_mapping(void *address, unsigned long size)
>> +{
>> +	unsigned long physaddr = (unsigned long)address - __PAGE_OFFSET;
>> +	pmdval_t pmd_flags, pmd;
>> +
>> +	if (!sme_me_mask)
>> +		return;
>> +
>> +	/* Clear the encryption mask from the early_pmd_flags */
>> +	pmd_flags = early_pmd_flags & ~sme_me_mask;
>> +
>> +	do {
>> +		pmd = (physaddr & PMD_MASK) + pmd_flags;
>> +		__early_make_pgtable((unsigned long)address, pmd);
>> +
>> +		address += PMD_SIZE;
>> +		physaddr += PMD_SIZE;
>> +		size = (size < PMD_SIZE) ? 0 : size - PMD_SIZE;
>> +	} while (size);
>> +}
>> +
>> +static void __init __clear_mapping(unsigned long address)
> 
> Should be called something with "pmd" in the name as it clears a PMD,
> i.e. __clear_pmd_mapping or so.

Ok.

> 
>> +{
>> +	unsigned long physaddr = address - __PAGE_OFFSET;
>> +	pgdval_t pgd, *pgd_p;
>> +	pudval_t pud, *pud_p;
>> +	pmdval_t *pmd_p;
>> +
>> +	/* Invalid address or early pgt is done ?  */
>> +	if (physaddr >= MAXMEM ||
>> +	    read_cr3() != __sme_pa_nodebug(early_level4_pgt))
>> +		return;
>> +
>> +	pgd_p = &early_level4_pgt[pgd_index(address)].pgd;
>> +	pgd = *pgd_p;
>> +
>> +	if (!pgd)
>> +		return;
>> +
>> +	/*
>> +	 * The use of __START_KERNEL_map rather than __PAGE_OFFSET here matches
>> +	 * __early_make_pgtable where the entry was created.
>> +	 */
>> +	pud_p = (pudval_t *)((pgd & PTE_PFN_MASK) + __START_KERNEL_map - phys_base);
>> +	pud_p += pud_index(address);
>> +	pud = *pud_p;
>> +
>> +	if (!pud)
>> +		return;
>> +
>> +	pmd_p = (pmdval_t *)((pud & PTE_PFN_MASK) + __START_KERNEL_map - phys_base);
>> +	pmd_p[pmd_index(address)] = 0;
>> +}
>> +
>> +static void __init clear_mapping(void *address, unsigned long size)
>> +{
>> +	if (!sme_me_mask)
>> +		return;
>> +
>> +	do {
>> +		__clear_mapping((unsigned long)address);
>> +
>> +		address += PMD_SIZE;
>> +		size = (size < PMD_SIZE) ? 0 : size - PMD_SIZE;
>> +	} while (size);
>> +}
>> +
>> +static void __init sme_memcpy(void *dst, void *src, unsigned long size)
>> +{
>> +	create_unencrypted_mapping(src, size);
>> +	memcpy(dst, src, size);
>> +	clear_mapping(src, size);
>> +}
>> +
> 
> In any case, this whole functionality is SME-specific and should be
> somewhere in an SME-specific file. arch/x86/mm/mem_encrypt.c or so...

I can look into that.  The reason I put this here is this is all the
early page fault support that is very specific to this file. I modified
an existing static function to take advantage of the mapping support.

> 
>>  /* Don't add a printk in there. printk relies on the PDA which is not initialized 
>>     yet. */
>>  static void __init clear_bss(void)
>> @@ -122,12 +205,12 @@ static void __init copy_bootdata(char *real_mode_data)
>>  	char * command_line;
>>  	unsigned long cmd_line_ptr;
>>  
>> -	memcpy(&boot_params, real_mode_data, sizeof boot_params);
>> +	sme_memcpy(&boot_params, real_mode_data, sizeof boot_params);
> 
> checkpatch.pl:
> 
> WARNING: sizeof boot_params should be sizeof(boot_params)
> #155: FILE: arch/x86/kernel/head64.c:208:
> +       sme_memcpy(&boot_params, real_mode_data, sizeof boot_params);

I can fix that.

> 
>>  	sanitize_boot_params(&boot_params);
>>  	cmd_line_ptr = get_cmd_line_ptr();
>>  	if (cmd_line_ptr) {
>>  		command_line = __va(cmd_line_ptr);
>> -		memcpy(boot_command_line, command_line, COMMAND_LINE_SIZE);
>> +		sme_memcpy(boot_command_line, command_line, COMMAND_LINE_SIZE);
>>  	}
>>  }
>>  
>> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
>> index 1489da8..1fdaa11 100644
>> --- a/arch/x86/kernel/setup.c
>> +++ b/arch/x86/kernel/setup.c
>> @@ -114,6 +114,7 @@
>>  #include <asm/microcode.h>
>>  #include <asm/mmu_context.h>
>>  #include <asm/kaslr.h>
>> +#include <asm/mem_encrypt.h>
>>  
>>  /*
>>   * max_low_pfn_mapped: highest direct mapped pfn under 4GB
>> @@ -376,6 +377,13 @@ static void __init reserve_initrd(void)
>>  	    !ramdisk_image || !ramdisk_size)
>>  		return;		/* No initrd provided by bootloader */
>>  
>> +	/*
>> +	 * This memory is marked encrypted by the kernel but the ramdisk
>> +	 * was loaded in the clear by the bootloader, so make sure that
>> +	 * the ramdisk image is encrypted.
>> +	 */
>> +	sme_early_mem_enc(ramdisk_image, ramdisk_end - ramdisk_image);
> 
> What happens if we go and relocate the ramdisk? I.e., the function above
> this one: relocate_initrd(). We have to encrypt it then too, I presume.

Hmmm, maybe... With the change to the early_memremap() the initrd is now
identified as BOOT_DATA in relocate_initrd() and so it will be mapped
and copied as non-encyrpted data. But since it was encrypted before the
call to relocate_initrd() it will copy encrypted bytes which will later
be accessed encrypted. That isn't clear though, so I'll rework
reserve_initrd() to perform the sme_early_mem_enc() once at the end
whether the initrd is re-located or not.

Thanks,
Tom

>