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SubjectRe: [RFC PATCH v3 06/20] x86: Add support to enable SME during early boot processing
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On 11/14/2016 11:29 AM, Borislav Petkov wrote:
> On Wed, Nov 09, 2016 at 06:35:43PM -0600, Tom Lendacky wrote:
>> This patch adds support to the early boot code to use Secure Memory
>> Encryption (SME). Support is added to update the early pagetables with
>> the memory encryption mask and to encrypt the kernel in place.
>>
>> The routines to set the encryption mask and perform the encryption are
>> stub routines for now with full function to be added in a later patch.
>>
>> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
>> ---
>> arch/x86/kernel/Makefile | 2 ++
>> arch/x86/kernel/head_64.S | 35 ++++++++++++++++++++++++++++++++++-
>> arch/x86/kernel/mem_encrypt_init.c | 29 +++++++++++++++++++++++++++++
>> 3 files changed, 65 insertions(+), 1 deletion(-)
>> create mode 100644 arch/x86/kernel/mem_encrypt_init.c
>>
>> diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
>> index 45257cf..27e22f4 100644
>> --- a/arch/x86/kernel/Makefile
>> +++ b/arch/x86/kernel/Makefile
>> @@ -141,4 +141,6 @@ ifeq ($(CONFIG_X86_64),y)
>>
>> obj-$(CONFIG_PCI_MMCONFIG) += mmconf-fam10h_64.o
>> obj-y += vsmp_64.o
>> +
>> + obj-y += mem_encrypt_init.o
>> endif
>> diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
>> index c98a559..9a28aad 100644
>> --- a/arch/x86/kernel/head_64.S
>> +++ b/arch/x86/kernel/head_64.S
>> @@ -95,6 +95,17 @@ startup_64:
>> jnz bad_address
>>
>> /*
>> + * Enable Secure Memory Encryption (if available). Save the mask
>> + * in %r12 for later use and add the memory encryption mask to %rbp
>> + * to include it in the page table fixups.
>> + */
>> + push %rsi
>> + call sme_enable
>> + pop %rsi
>
> Why %rsi?
>
> sme_enable() is void so no args in registers and returns in %rax.
>
> /me is confused.

The %rsi register can be clobbered by the called function so I'm saving
it since it points to the real mode data. I might be able to look into
saving it earlier and restoring it before needed, but I though this
might be clearer.

>
>> + movq %rax, %r12
>> + addq %r12, %rbp
>> +
>> + /*
>> * Fixup the physical addresses in the page table
>> */
>> addq %rbp, early_level4_pgt + (L4_START_KERNEL*8)(%rip)
>> @@ -117,6 +128,7 @@ startup_64:
>> shrq $PGDIR_SHIFT, %rax
>>
>> leaq (4096 + _KERNPG_TABLE)(%rbx), %rdx
>> + addq %r12, %rdx
>> movq %rdx, 0(%rbx,%rax,8)
>> movq %rdx, 8(%rbx,%rax,8)
>>
>> @@ -133,6 +145,7 @@ startup_64:
>> movq %rdi, %rax
>> shrq $PMD_SHIFT, %rdi
>> addq $(__PAGE_KERNEL_LARGE_EXEC & ~_PAGE_GLOBAL), %rax
>> + addq %r12, %rax
>> leaq (_end - 1)(%rip), %rcx
>> shrq $PMD_SHIFT, %rcx
>> subq %rdi, %rcx
>> @@ -163,9 +176,21 @@ startup_64:
>> cmp %r8, %rdi
>> jne 1b
>>
>> - /* Fixup phys_base */
>> + /*
>> + * Fixup phys_base, remove the memory encryption mask from %rbp
>> + * to obtain the true physical address.
>> + */
>> + subq %r12, %rbp
>> addq %rbp, phys_base(%rip)
>>
>> + /*
>> + * The page tables have been updated with the memory encryption mask,
>> + * so encrypt the kernel if memory encryption is active
>> + */
>> + push %rsi
>> + call sme_encrypt_kernel
>> + pop %rsi
>
> Ditto.
>
>> +
>> movq $(early_level4_pgt - __START_KERNEL_map), %rax
>> jmp 1f
>> ENTRY(secondary_startup_64)
>> @@ -186,9 +211,17 @@ ENTRY(secondary_startup_64)
>> /* Sanitize CPU configuration */
>> call verify_cpu
>>
>> + push %rsi
>> + call sme_get_me_mask
>> + pop %rsi
>
> Ditto.
>
>> + movq %rax, %r12
>> +
>> movq $(init_level4_pgt - __START_KERNEL_map), %rax
>> 1:
>>
>> + /* Add the memory encryption mask to RAX */
>
> I think that should say something like:
>
> /*
> * Add the memory encryption mask to init_level4_pgt's physical address
> */
>
> or so...

Yup, I'll expand on the comment for this.

>
>> + addq %r12, %rax
>> +
>> /* Enable PAE mode and PGE */
>> movl $(X86_CR4_PAE | X86_CR4_PGE), %ecx
>> movq %rcx, %cr4
>> diff --git a/arch/x86/kernel/mem_encrypt_init.c b/arch/x86/kernel/mem_encrypt_init.c
>> new file mode 100644
>> index 0000000..388d6fb
>> --- /dev/null
>> +++ b/arch/x86/kernel/mem_encrypt_init.c
>
> So nothing in the commit message explains why we need a separate
> mem_encrypt_init.c file when we already have arch/x86/mm/mem_encrypt.c
> for all memory encryption code...

I can expand on the commit message about that. I was trying to keep the
early boot-related code separate from the main code in arch/x86/mm dir.

Thanks,
Tom

>
>> @@ -0,0 +1,29 @@
>> +/*
>> + * AMD Memory Encryption Support
>> + *
>> + * Copyright (C) 2016 Advanced Micro Devices, Inc.
>> + *
>> + * Author: Tom Lendacky <thomas.lendacky@amd.com>
>> + *
>> + * This program is free software; you can redistribute it and/or modify
>> + * it under the terms of the GNU General Public License version 2 as
>> + * published by the Free Software Foundation.
>> + */
>> +
>> +#include <linux/linkage.h>
>> +#include <linux/init.h>
>> +#include <linux/mem_encrypt.h>
>> +
>> +void __init sme_encrypt_kernel(void)
>> +{
>> +}
>> +
>> +unsigned long __init sme_get_me_mask(void)
>> +{
>> + return sme_me_mask;
>> +}
>> +
>> +unsigned long __init sme_enable(void)
>> +{
>> + return sme_me_mask;
>> +}
>

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