Re: [PATCH v5 17/32] x86/mm: Add support to access boot related data in the clear

Borislav Petkov
2017-05-15T18:35:49Z

On Tue, Apr 18, 2017 at 04:19:21PM -0500, Tom Lendacky wrote:
> Boot data (such as EFI related data) is not encrypted when the system is
> booted because UEFI/BIOS does not run with SME active. In order to access
> this data properly it needs to be mapped decrypted.
>
> The early_memremap() support is updated to provide an arch specific

"Update early_memremap() to provide... "

> routine to modify the pagetable protection attributes before they are
> applied to the new mapping. This is used to remove the encryption mask
> for boot related data.
>
> The memremap() support is updated to provide an arch specific routine

Ditto. Passive tone always reads harder than an active tone,
"doer"-sentence.

> to determine if RAM remapping is allowed. RAM remapping will cause an
> encrypted mapping to be generated. By preventing RAM remapping,
> ioremap_cache() will be used instead, which will provide a decrypted
> mapping of the boot related data.
>
> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
> ---
> arch/x86/include/asm/io.h | 4 +
> arch/x86/mm/ioremap.c | 182 +++++++++++++++++++++++++++++++++++++++++++++
> include/linux/io.h | 2
> kernel/memremap.c | 20 ++++-
> mm/early_ioremap.c | 18 ++++
> 5 files changed, 219 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
> index 7afb0e2..75f2858 100644
> --- a/arch/x86/include/asm/io.h
> +++ b/arch/x86/include/asm/io.h
> @@ -381,4 +381,8 @@ extern int __must_check arch_phys_wc_add(unsigned long base,
> #define arch_io_reserve_memtype_wc arch_io_reserve_memtype_wc
> #endif
>
> +extern bool arch_memremap_do_ram_remap(resource_size_t offset, size_t size,
> + unsigned long flags);
> +#define arch_memremap_do_ram_remap arch_memremap_do_ram_remap
> +
> #endif /* _ASM_X86_IO_H */
> diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
> index 9bfcb1f..bce0604 100644
> --- a/arch/x86/mm/ioremap.c
> +++ b/arch/x86/mm/ioremap.c
> @@ -13,6 +13,7 @@
> #include <linux/slab.h>
> #include <linux/vmalloc.h>
> #include <linux/mmiotrace.h>
> +#include <linux/efi.h>
>
> #include <asm/cacheflush.h>
> #include <asm/e820/api.h>
> @@ -21,6 +22,7 @@
> #include <asm/tlbflush.h>
> #include <asm/pgalloc.h>
> #include <asm/pat.h>
> +#include <asm/setup.h>
>
> #include "physaddr.h"
>
> @@ -419,6 +421,186 @@ void unxlate_dev_mem_ptr(phys_addr_t phys, void *addr)
> iounmap((void __iomem *)((unsigned long)addr & PAGE_MASK));
> }
>
> +/*
> + * Examine the physical address to determine if it is an area of memory
> + * that should be mapped decrypted. If the memory is not part of the
> + * kernel usable area it was accessed and created decrypted, so these
> + * areas should be mapped decrypted.
> + */
> +static bool memremap_should_map_decrypted(resource_size_t phys_addr,
> + unsigned long size)
> +{
> + /* Check if the address is outside kernel usable area */
> + switch (e820__get_entry_type(phys_addr, phys_addr + size - 1)) {
> + case E820_TYPE_RESERVED:
> + case E820_TYPE_ACPI:
> + case E820_TYPE_NVS:
> + case E820_TYPE_UNUSABLE:
> + return true;
> + default:
> + break;
> + }
> +
> + return false;
> +}
> +
> +/*
> + * Examine the physical address to determine if it is EFI data. Check
> + * it against the boot params structure and EFI tables and memory types.
> + */
> +static bool memremap_is_efi_data(resource_size_t phys_addr,
> + unsigned long size)
> +{
> + u64 paddr;
> +
> + /* Check if the address is part of EFI boot/runtime data */
> + if (efi_enabled(EFI_BOOT)) {

Save indentation level:

if (!efi_enabled(EFI_BOOT))
return false;

> + 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;

So those two above look like could be two global vars which are
initialized somewhere in the EFI init path:

efi_memmap_phys and efi_systab_phys or so.

Matt ?

And then you won't need to create that paddr each time on the fly. I
mean, it's not a lot of instructions but still...

> + if (phys_addr == paddr)
> + return true;
> +
> + if (efi_table_address_match(phys_addr))
> + return true;
> +
> + switch (efi_mem_type(phys_addr)) {
> + case EFI_BOOT_SERVICES_DATA:
> + case EFI_RUNTIME_SERVICES_DATA:
> + return true;
> + default:
> + break;
> + }
> + }
> +
> + return false;
> +}
> +
> +/*
> + * Examine the physical address to determine if it is boot data by checking
> + * it against the boot params setup_data chain.
> + */
> +static bool memremap_is_setup_data(resource_size_t phys_addr,
> + unsigned long size)
> +{
> + struct setup_data *data;
> + u64 paddr, paddr_next;
> +
> + paddr = boot_params.hdr.setup_data;
> + while (paddr) {
> + bool is_setup_data = false;

You don't need that bool:

static bool memremap_is_setup_data(resource_size_t phys_addr,
unsigned long size)
{
struct setup_data *data;
u64 paddr, paddr_next;

paddr = boot_params.hdr.setup_data;
while (paddr) {
if (phys_addr == paddr)
return true;

data = memremap(paddr, sizeof(*data), MEMREMAP_WB | MEMREMAP_DEC);

paddr_next = data->next;

if ((phys_addr > paddr) && (phys_addr < (paddr + data->len))) {
memunmap(data);
return true;
}

memunmap(data);

paddr = paddr_next;
}
return false;
}

Flow is a bit clearer.

> +/*
> + * Examine the physical address to determine if it is boot data by checking
> + * it against the boot params setup_data chain (early boot version).
> + */
> +static bool __init early_memremap_is_setup_data(resource_size_t phys_addr,
> + unsigned long size)
> +{
> + struct setup_data *data;
> + u64 paddr, paddr_next;
> +
> + paddr = boot_params.hdr.setup_data;
> + while (paddr) {
> + bool is_setup_data = false;
> +
> + if (phys_addr == paddr)
> + return true;
> +
> + data = early_memremap_decrypted(paddr, sizeof(*data));
> +
> + paddr_next = data->next;
> +
> + if ((phys_addr > paddr) && (phys_addr < (paddr + data->len)))
> + is_setup_data = true;
> +
> + early_memunmap(data, sizeof(*data));
> +
> + if (is_setup_data)
> + return true;
> +
> + paddr = paddr_next;
> + }
> +
> + return false;
> +}

This one is begging to be unified with memremap_is_setup_data() to both
call a __ worker function.

> +
> +/*
> + * Architecture function to determine if RAM remap is allowed. By default, a
> + * RAM remap will map the data as encrypted. Determine if a RAM remap should
> + * not be done so that the data will be mapped decrypted.
> + */
> +bool arch_memremap_do_ram_remap(resource_size_t phys_addr, unsigned long size,
> + unsigned long flags)

So this function doesn't do anything - it replies to a yes/no question.
So the name should not say "do" but sound like a question. Maybe:

if (arch_memremap_can_remap( ... ))

or so...

> +{
> + if (!sme_active())
> + return true;
> +
> + if (flags & MEMREMAP_ENC)
> + return true;
> +
> + if (flags & MEMREMAP_DEC)
> + return false;

So this looks strange to me: both flags MEMREMAP_ENC and _DEC override
setup and efi data checking. But we want to remap setup and EFI data
*always* decrypted because that data was not encrypted as, as you say,
firmware doesn't run with SME active.

So my simple logic says that EFI stuff should *always* be mapped DEC,
regardless of flags. Ditto for setup data. So that check below should
actually *override* the flags checks and go before them, no?

> +
> + if (memremap_is_setup_data(phys_addr, size) ||
> + memremap_is_efi_data(phys_addr, size) ||
> + memremap_should_map_decrypted(phys_addr, size))
> + return false;
> +
> + return true;
> +}
> +
> +/*
> + * Architecture override of __weak function to adjust the protection attributes
> + * used when remapping memory. By default, early_memremp() will map the data

early_memremAp() - a is missing.

--
Regards/Gruss,
Boris.

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