Re: [RFC PATCH v3 10/20] Add support to access boot related data in the clear

From: Borislav Petkov
Date: Thu Nov 17 2016 - 12:51:02 EST

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On Wed, Nov 09, 2016 at 06:36:31PM -0600, Tom Lendacky wrote:
> Boot data (such as EFI related data) is not encrypted when the system is
> booted and needs to be accessed unencrypted. Add support to apply the
> proper attributes to the EFI page tables and to the early_memremap and
> memremap APIs to identify the type of data being accessed so that the
> proper encryption attribute can be applied.
>
> Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
> ---
> arch/x86/include/asm/e820.h | 1
> arch/x86/kernel/e820.c | 16 +++++++
> arch/x86/mm/ioremap.c | 89 ++++++++++++++++++++++++++++++++++++++++
> arch/x86/platform/efi/efi_64.c | 12 ++++-
> drivers/firmware/efi/efi.c | 33 +++++++++++++++
> include/linux/efi.h | 2 +
> kernel/memremap.c | 8 +++-
> mm/early_ioremap.c | 18 +++++++-
> 8 files changed, 172 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/include/asm/e820.h b/arch/x86/include/asm/e820.h
> index 476b574..186f1d04 100644
> --- a/arch/x86/include/asm/e820.h
> +++ b/arch/x86/include/asm/e820.h
> @@ -16,6 +16,7 @@ extern struct e820map *e820_saved;
> extern unsigned long pci_mem_start;
> extern int e820_any_mapped(u64 start, u64 end, unsigned type);
> extern int e820_all_mapped(u64 start, u64 end, unsigned type);
> +extern unsigned int e820_get_entry_type(u64 start, u64 end);
> extern void e820_add_region(u64 start, u64 size, int type);
> extern void e820_print_map(char *who);
> extern int
> diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
> index b85fe5f..92fce4e 100644
> --- a/arch/x86/kernel/e820.c
> +++ b/arch/x86/kernel/e820.c
> @@ -107,6 +107,22 @@ int __init e820_all_mapped(u64 start, u64 end, unsigned type)
> return 0;
> }
>
> +unsigned int e820_get_entry_type(u64 start, u64 end)
> +{
> + int i;
> +
> + for (i = 0; i < e820->nr_map; i++) {
> + struct e820entry *ei = &e820->map[i];
> +
> + if (ei->addr >= end || ei->addr + ei->size <= start)
> + continue;
> +
> + return ei->type;
> + }
> +
> + return 0;

Please add a

#define E820_TYPE_INVALID 0

or so and return it instead of the naked number 0.

Also, this patch can be split in logical parts. The e820 stuff can be a
separate pre-patch.

efi_table_address_match() and the tables definitions is a second pre-patch.

The rest is then the third patch.

...

> +}
> +
> /*
> * Add a memory region to the kernel e820 map.
> */
> diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
> index ff542cd..ee347c2 100644
> --- a/arch/x86/mm/ioremap.c
> +++ b/arch/x86/mm/ioremap.c
> @@ -20,6 +20,9 @@
> #include <asm/tlbflush.h>
> #include <asm/pgalloc.h>
> #include <asm/pat.h>
> +#include <asm/e820.h>
> +#include <asm/setup.h>
> +#include <linux/efi.h>
>
> #include "physaddr.h"
>
> @@ -418,6 +421,92 @@ void unxlate_dev_mem_ptr(phys_addr_t phys, void *addr)
> iounmap((void __iomem *)((unsigned long)addr & PAGE_MASK));
> }
>
> +static bool memremap_setup_data(resource_size_t phys_addr,
> + unsigned long size)

This function name doesn't read like what the function does.

> +{
> + u64 paddr;
> +
> + if (phys_addr == boot_params.hdr.setup_data)
> + return true;
> +
> + paddr = boot_params.efi_info.efi_memmap_hi;
> + paddr <<= 32;
> + paddr |= boot_params.efi_info.efi_memmap;
> + if (phys_addr == paddr)
> + return true;
> +
> + paddr = boot_params.efi_info.efi_systab_hi;
> + paddr <<= 32;
> + paddr |= boot_params.efi_info.efi_systab;
> + if (phys_addr == paddr)
> + return true;
> +
> + if (efi_table_address_match(phys_addr))
> + return true;
> +
> + return false;
> +}

arch/x86/built-in.o: In function `memremap_setup_data':
/home/boris/kernel/alt-linux/arch/x86/mm/ioremap.c:444: undefined reference to `efi_table_address_match'
arch/x86/built-in.o: In function `memremap_apply_encryption':
/home/boris/kernel/alt-linux/arch/x86/mm/ioremap.c:462: undefined reference to `efi_mem_type'
make: *** [vmlinux] Error 1

I guess due to

# CONFIG_EFI is not set

> +
> +static bool memremap_apply_encryption(resource_size_t phys_addr,
> + unsigned long size)

This name is misleading too: it doesn't apply encryption but checks
whether to apply encryption for @phys_addr or not. So something like:

... memremap_should_encrypt(...)
{
return true - for should
return false - for should not

should make the whole thing much more straightforward. Or am I
misunderstanding you here?

> +{
> + /* SME is not active, just return true */
> + if (!sme_me_mask)
> + return true;

I don't understand the logic here: SME is not active -> apply encryption?!

> +
> + /* Check if the address is part of the setup data */

That comment belongs over the function definition of
memremap_setup_data() along with what it is supposed to do.

> + if (memremap_setup_data(phys_addr, size))
> + return false;
> +
> + /* Check if the address is part of EFI boot/runtime data */
> + switch (efi_mem_type(phys_addr)) {

Please send a pre-patch fix for efi_mem_type() to return
EFI_RESERVED_TYPE instead of naked 0 in the failure case.

> + case EFI_BOOT_SERVICES_DATA:
> + case EFI_RUNTIME_SERVICES_DATA:
> + return false;
> + }
> +
> + /* Check if the address is outside kernel usable area */
> + switch (e820_get_entry_type(phys_addr, phys_addr + size - 1)) {
> + case E820_RESERVED:
> + case E820_ACPI:
> + case E820_NVS:
> + case E820_UNUSABLE:
> + return false;
> + }
> +
> + return true;
> +}
> +
> +/*
> + * Architecure override of __weak function to prevent ram remap and use the

s/ram/RAM/

> + * architectural remap function.
> + */
> +bool memremap_do_ram_remap(resource_size_t phys_addr, unsigned long size)
> +{
> + if (!memremap_apply_encryption(phys_addr, size))
> + return false;
> +
> + return true;

Do I see it correctly that this could just very simply be:

return memremap_apply_encryption(phys_addr, size);

?

> +}
> +
> +/*
> + * Architecure override of __weak function to adjust the protection attributes
> + * used when remapping memory.
> + */
> +pgprot_t __init early_memremap_pgprot_adjust(resource_size_t phys_addr,
> + unsigned long size,
> + pgprot_t prot)
> +{
> + unsigned long prot_val = pgprot_val(prot);
> +
> + if (memremap_apply_encryption(phys_addr, size))
> + prot_val |= _PAGE_ENC;
> + else
> + prot_val &= ~_PAGE_ENC;
> +
> + return __pgprot(prot_val);
> +}
> +
> /* Remap memory with encryption */
> void __init *early_memremap_enc(resource_size_t phys_addr,
> unsigned long size)
> diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
> index 58b0f80..3f89179 100644
> --- a/arch/x86/platform/efi/efi_64.c
> +++ b/arch/x86/platform/efi/efi_64.c
> @@ -221,7 +221,13 @@ int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages)
> if (efi_enabled(EFI_OLD_MEMMAP))
> return 0;
>
> - efi_scratch.efi_pgt = (pgd_t *)__pa(efi_pgd);
> + /*
> + * Since the PGD is encrypted, set the encryption mask so that when
> + * this value is loaded into cr3 the PGD will be decrypted during
> + * the pagetable walk.
> + */
> + efi_scratch.efi_pgt = (pgd_t *)__sme_pa(efi_pgd);
> +
> pgd = efi_pgd;
>
> /*
> @@ -231,7 +237,7 @@ int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages)
> * phys_efi_set_virtual_address_map().
> */
> pfn = pa_memmap >> PAGE_SHIFT;
> - if (kernel_map_pages_in_pgd(pgd, pfn, pa_memmap, num_pages, _PAGE_NX | _PAGE_RW)) {
> + if (kernel_map_pages_in_pgd(pgd, pfn, pa_memmap, num_pages, _PAGE_NX | _PAGE_RW | _PAGE_ENC)) {

That line sticks too far out, let's shorten it:

unsigned long pf = _PAGE_NX | _PAGE_RW | _PAGE_ENC;

...

if (kernel_map_pages_in_pgd(pgd, pfn, pa_memmap, num_pages, pf)) {

..

pf = _PAGE_RW | _PAGE_ENC;
if (kernel_map_pages_in_pgd(pgd, pfn, text, npages, pf)) {

..

> pr_err("Error ident-mapping new memmap (0x%lx)!\n", pa_memmap);
> return 1;
> }
> @@ -258,7 +264,7 @@ int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages)
> text = __pa(_text);
> pfn = text >> PAGE_SHIFT;
>
> - if (kernel_map_pages_in_pgd(pgd, pfn, text, npages, _PAGE_RW)) {
> + if (kernel_map_pages_in_pgd(pgd, pfn, text, npages, _PAGE_RW | _PAGE_ENC)) {
> pr_err("Failed to map kernel text 1:1\n");
> return 1;
> }
> diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> index 1ac199c..91c06ec 100644
> --- a/drivers/firmware/efi/efi.c
> +++ b/drivers/firmware/efi/efi.c
> @@ -51,6 +51,25 @@ struct efi __read_mostly efi = {
> };
> EXPORT_SYMBOL(efi);
>
> +static unsigned long *efi_tables[] = {
> + &efi.mps,
> + &efi.acpi,
> + &efi.acpi20,
> + &efi.smbios,
> + &efi.smbios3,
> + &efi.sal_systab,
> + &efi.boot_info,
> + &efi.hcdp,
> + &efi.uga,
> + &efi.uv_systab,
> + &efi.fw_vendor,
> + &efi.runtime,
> + &efi.config_table,
> + &efi.esrt,
> + &efi.properties_table,
> + &efi.mem_attr_table,
> +};
> +
> static bool disable_runtime;
> static int __init setup_noefi(char *arg)
> {
> @@ -822,3 +841,17 @@ int efi_status_to_err(efi_status_t status)
>
> return err;
> }
> +
> +bool efi_table_address_match(unsigned long phys_addr)
> +{
> + int i;
> +
> + if (phys_addr == EFI_INVALID_TABLE_ADDR)
> + return false;
> +
> + for (i = 0; i < ARRAY_SIZE(efi_tables); i++)
> + if (*(efi_tables[i]) == phys_addr)
> + return true;
> +
> + return false;
> +}
> diff --git a/include/linux/efi.h b/include/linux/efi.h
> index 2d08948..72d89bf 100644
> --- a/include/linux/efi.h
> +++ b/include/linux/efi.h
> @@ -1070,6 +1070,8 @@ efi_capsule_pending(int *reset_type)
>
> extern int efi_status_to_err(efi_status_t status);
>
> +extern bool efi_table_address_match(unsigned long phys_addr);
> +
> /*
> * Variable Attributes
> */
> diff --git a/kernel/memremap.c b/kernel/memremap.c
> index b501e39..ac1437e 100644
> --- a/kernel/memremap.c
> +++ b/kernel/memremap.c
> @@ -34,12 +34,18 @@ static void *arch_memremap_wb(resource_size_t offset, unsigned long size)
> }
> #endif
>
> +bool __weak memremap_do_ram_remap(resource_size_t offset, size_t size)
> +{
> + return true;
> +}
> +

Why isn't this an inline in a header?

> static void *try_ram_remap(resource_size_t offset, size_t size)
> {
> unsigned long pfn = PHYS_PFN(offset);
>
> /* In the simple case just return the existing linear address */
> - if (pfn_valid(pfn) && !PageHighMem(pfn_to_page(pfn)))
> + if (pfn_valid(pfn) && !PageHighMem(pfn_to_page(pfn)) &&
> + memremap_do_ram_remap(offset, size))
> return __va(offset);

<---- newline here.

> return NULL; /* fallback to arch_memremap_wb */
> }
> diff --git a/mm/early_ioremap.c b/mm/early_ioremap.c
> index d71b98b..34af5b6 100644
> --- a/mm/early_ioremap.c
> +++ b/mm/early_ioremap.c
> @@ -30,6 +30,13 @@ early_param("early_ioremap_debug", early_ioremap_debug_setup);
>
> static int after_paging_init __initdata;
>
> +pgprot_t __init __weak early_memremap_pgprot_adjust(resource_size_t phys_addr,
> + unsigned long size,
> + pgprot_t prot)
> +{
> + return prot;
> +}

Also, why isn't this an inline in a header somewhere?

--
Regards/Gruss,
Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

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