Re: [RFC PATCH v4 07/28] x86: Provide general kernel support for memory encryption

Borislav Petkov
2017-02-20T15:21:52Z

On Thu, Feb 16, 2017 at 09:43:32AM -0600, Tom Lendacky wrote:
> Adding general kernel support for memory encryption includes:
> - Modify and create some page table macros to include the Secure Memory
> Encryption (SME) memory encryption mask

Let's not write it like some technical document: "Secure Memory
Encryption (SME) mask" is perfectly fine.

> - Modify and create some macros for calculating physical and virtual
> memory addresses
> - Provide an SME initialization routine to update the protection map with
> the memory encryption mask so that it is used by default
> - #undef CONFIG_AMD_MEM_ENCRYPT in the compressed boot path

These bulletpoints talk about the "what" this patch does but they should
talk about the "why".

For example, it doesn't say why we're using _KERNPG_TABLE_NOENC when
building the initial pagetable and that would be an interesting piece of
information.

> Signed-off-by: Tom Lendacky <thomas.lendacky-5C7GfCeVMHo@public.gmane.org>
> ---
> arch/x86/boot/compressed/pagetable.c | 7 +++++
> arch/x86/include/asm/fixmap.h | 7 +++++
> arch/x86/include/asm/mem_encrypt.h | 14 +++++++++++
> arch/x86/include/asm/page.h | 4 ++-
> arch/x86/include/asm/pgtable.h | 26 ++++++++++++++------
> arch/x86/include/asm/pgtable_types.h | 45 ++++++++++++++++++++++------------
> arch/x86/include/asm/processor.h | 3 ++
> arch/x86/kernel/espfix_64.c | 2 +-
> arch/x86/kernel/head64.c | 12 ++++++++-
> arch/x86/kernel/head_64.S | 18 +++++++-------
> arch/x86/mm/kasan_init_64.c | 4 ++-
> arch/x86/mm/mem_encrypt.c | 20 +++++++++++++++
> arch/x86/mm/pageattr.c | 3 ++
> include/asm-generic/pgtable.h | 8 ++++++
> 14 files changed, 133 insertions(+), 40 deletions(-)
>
> diff --git a/arch/x86/boot/compressed/pagetable.c b/arch/x86/boot/compressed/pagetable.c
> index 56589d0..411c443 100644
> --- a/arch/x86/boot/compressed/pagetable.c
> +++ b/arch/x86/boot/compressed/pagetable.c
> @@ -15,6 +15,13 @@
> #define __pa(x) ((unsigned long)(x))
> #define __va(x) ((void *)((unsigned long)(x)))
>
> +/*
> + * The pgtable.h and mm/ident_map.c includes make use of the SME related
> + * information which is not used in the compressed image support. Un-define
> + * the SME support to avoid any compile and link errors.
> + */
> +#undef CONFIG_AMD_MEM_ENCRYPT
> +
> #include "misc.h"
>
> /* These actually do the work of building the kernel identity maps. */
> diff --git a/arch/x86/include/asm/fixmap.h b/arch/x86/include/asm/fixmap.h
> index 8554f96..83e91f0 100644
> --- a/arch/x86/include/asm/fixmap.h
> +++ b/arch/x86/include/asm/fixmap.h
> @@ -153,6 +153,13 @@ static inline void __set_fixmap(enum fixed_addresses idx,
> }
> #endif
>
> +/*
> + * Fixmap settings used with memory encryption
> + * - FIXMAP_PAGE_NOCACHE is used for MMIO so make sure the memory
> + * encryption mask is not part of the page attributes

Make that a regular sentence.

> + */
> +#define FIXMAP_PAGE_NOCACHE PAGE_KERNEL_IO_NOCACHE
> +
> #include <asm-generic/fixmap.h>
>
> #define __late_set_fixmap(idx, phys, flags) __set_fixmap(idx, phys, flags)
> diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
> index ccc53b0..547989d 100644
> --- a/arch/x86/include/asm/mem_encrypt.h
> +++ b/arch/x86/include/asm/mem_encrypt.h
> @@ -15,6 +15,8 @@
>
> #ifndef __ASSEMBLY__
>
> +#include <linux/init.h>
> +
> #ifdef CONFIG_AMD_MEM_ENCRYPT
>
> extern unsigned long sme_me_mask;
> @@ -24,6 +26,11 @@ static inline bool sme_active(void)
> return (sme_me_mask) ? true : false;
> }
>
> +void __init sme_early_init(void);
> +
> +#define __sme_pa(x) (__pa((x)) | sme_me_mask)
> +#define __sme_pa_nodebug(x) (__pa_nodebug((x)) | sme_me_mask)

Right, I know we did talk about those but in looking more into the
future, you'd have to go educate people to use the __sme_pa* variants.
Otherwise, we'd have to go and fix up code on AMD SME machines because
someone used __pa_* variants where someone should have been using the
__sma_pa_* variants.

IOW, should we simply put sme_me_mask in the actual __pa* macro
definitions?

Or are we saying that the __sme_pa* versions you have above are
the special ones and we need them only in a handful of places like
load_cr3(), for example...? And the __pa_* ones should return the
physical address without the SME mask because callers don't need it?

> +
> #else /* !CONFIG_AMD_MEM_ENCRYPT */
>
> #ifndef sme_me_mask
> @@ -35,6 +42,13 @@ static inline bool sme_active(void)
> }
> #endif
>
> +static inline void __init sme_early_init(void)
> +{
> +}
> +
> +#define __sme_pa __pa
> +#define __sme_pa_nodebug __pa_nodebug
> +
> #endif /* CONFIG_AMD_MEM_ENCRYPT */
>
> #endif /* __ASSEMBLY__ */
> diff --git a/arch/x86/include/asm/page.h b/arch/x86/include/asm/page.h
> index cf8f619..b1f7bf6 100644
> --- a/arch/x86/include/asm/page.h
> +++ b/arch/x86/include/asm/page.h
> @@ -15,6 +15,8 @@
>
> #ifndef __ASSEMBLY__
>
> +#include <asm/mem_encrypt.h>
> +
> struct page;
>
> #include <linux/range.h>
> @@ -55,7 +57,7 @@ static inline void copy_user_page(void *to, void *from, unsigned long vaddr,
> __phys_addr_symbol(__phys_reloc_hide((unsigned long)(x)))
>
> #ifndef __va
> -#define __va(x) ((void *)((unsigned long)(x)+PAGE_OFFSET))
> +#define __va(x) ((void *)(((unsigned long)(x) & ~sme_me_mask) + PAGE_OFFSET))

You have a bunch of places where you remove the enc mask:

address & ~sme_me_mask

so you could do:

#define __sme_unmask(x) ((unsigned long)(x) & ~sme_me_mask)

and use it everywhere. "unmask" is what I could think of, there should
be a better, short name for it...

> #endif
>
> #define __boot_va(x) __va(x)
> diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
> index 2d81161..b41caab 100644
> --- a/arch/x86/include/asm/pgtable.h
> +++ b/arch/x86/include/asm/pgtable.h
> @@ -3,6 +3,7 @@

...

> @@ -563,8 +575,7 @@ static inline unsigned long pmd_page_vaddr(pmd_t pmd)
> * Currently stuck as a macro due to indirect forward reference to
> * linux/mmzone.h's __section_mem_map_addr() definition:
> */
> -#define pmd_page(pmd) \
> - pfn_to_page((pmd_val(pmd) & pmd_pfn_mask(pmd)) >> PAGE_SHIFT)
> +#define pmd_page(pmd) pfn_to_page(pmd_pfn(pmd))
>
> /*
> * the pmd page can be thought of an array like this: pmd_t[PTRS_PER_PMD]
> @@ -632,8 +643,7 @@ static inline unsigned long pud_page_vaddr(pud_t pud)
> * Currently stuck as a macro due to indirect forward reference to
> * linux/mmzone.h's __section_mem_map_addr() definition:
> */
> -#define pud_page(pud) \
> - pfn_to_page((pud_val(pud) & pud_pfn_mask(pud)) >> PAGE_SHIFT)
> +#define pud_page(pud) pfn_to_page(pud_pfn(pud))
>
> /* Find an entry in the second-level page table.. */
> static inline pmd_t *pmd_offset(pud_t *pud, unsigned long address)
> @@ -673,7 +683,7 @@ static inline unsigned long pgd_page_vaddr(pgd_t pgd)
> * Currently stuck as a macro due to indirect forward reference to
> * linux/mmzone.h's __section_mem_map_addr() definition:
> */
> -#define pgd_page(pgd) pfn_to_page(pgd_val(pgd) >> PAGE_SHIFT)
> +#define pgd_page(pgd) pfn_to_page(pgd_pfn(pgd))
>
> /* to find an entry in a page-table-directory. */
> static inline unsigned long pud_index(unsigned long address)

This conversion to *_pfn() is an unrelated cleanup. Pls carve it out and
put it in the front of the patchset as a separate patch.

...

> diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
> index b99d469..d71df97 100644
> --- a/arch/x86/mm/mem_encrypt.c
> +++ b/arch/x86/mm/mem_encrypt.c
> @@ -11,6 +11,10 @@
> */
>
> #include <linux/linkage.h>
> +#include <linux/init.h>
> +#include <linux/mm.h>
> +
> +extern pmdval_t early_pmd_flags;

WARNING: externs should be avoided in .c files
#476: FILE: arch/x86/mm/mem_encrypt.c:17:
+extern pmdval_t early_pmd_flags;

> /*
> * Since SME related variables are set early in the boot process they must
> @@ -19,3 +23,19 @@
> */
> unsigned long sme_me_mask __section(.data) = 0;
> EXPORT_SYMBOL_GPL(sme_me_mask);
> +
> +void __init sme_early_init(void)
> +{
> + unsigned int i;
> +
> + if (!sme_me_mask)
> + return;
> +
> + early_pmd_flags |= sme_me_mask;
> +
> + __supported_pte_mask |= sme_me_mask;
> +
> + /* Update the protection map with memory encryption mask */
> + for (i = 0; i < ARRAY_SIZE(protection_map); i++)
> + protection_map[i] = pgprot_encrypted(protection_map[i]);
> +}

--
Regards/Gruss,
Boris.

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