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

Tom Lendacky
2017-05-17T18:54:56Z

On 5/15/2017 1:35 PM, Borislav Petkov wrote:
> 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... "

Will do.

>
>> 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.

Ditto.

>
>> 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;
>

I was worried what the compiler might do when CONFIG_EFI is not set,
but it appears to take care of it. I'll double check though.

>
>> + 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.

I may introduce a length variable to capture data->len right after
paddr_next is set and then have just a single memunmap() call before
the if check.

>
>> +/*
>> + * 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.

I tried that, but calling an "__init" function (early_memremap()) from
a non "__init" function generated warnings. I suppose I can pass in a
function for the map and unmap but that looks worse to me (also the
unmap functions take different arguments).

>
>> +
>> +/*
>> + * 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...

Ok, I'll change that.

>
>> +{
>> + 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?

This is like the chicken and the egg scenario. In order to determine if
an address is setup data I have to explicitly map the setup data chain
as decrypted. In order to do that I have to supply a flag to explicitly
map the data decrypted otherwise I wind up back in the
memremap_is_setup_data() function again and again and again...

>
>> +
>> + 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.

Got it.

Thanks,
Tom

>