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Date: Sat, 11 Mar 2023 18:14:32 +0300
From: Evgeniy Baskov <baskov@...ras.ru>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>, Andy Lutomirski <luto@...nel.org>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
Alexey Khoroshilov <khoroshilov@...ras.ru>,
Peter Jones <pjones@...hat.com>,
"Limonciello, Mario" <mario.limonciello@....com>,
joeyli <jlee@...e.com>, lvc-project@...uxtesting.org,
x86@...nel.org, linux-efi@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v4 23/26] efi/libstub: Use memory attribute protocol
On 2023-03-10 19:13, Ard Biesheuvel wrote:
> On Thu, 15 Dec 2022 at 13:42, Evgeniy Baskov <baskov@...ras.ru> wrote:
>>
>> Add EFI_MEMORY_ATTRIBUTE_PROTOCOL as preferred alternative to DXE
>> services for changing memory attributes in the EFISTUB.
>>
>> Use DXE services only as a fallback in case aforementioned protocol
>> is not supported by UEFI implementation.
>>
>> Move DXE services initialization code closer to the place they are
>> used
>> to match EFI_MEMORY_ATTRIBUTE_PROTOCOL initialization code.
>>
>> Tested-by: Mario Limonciello <mario.limonciello@....com>
>> Tested-by: Peter Jones <pjones@...hat.com>
>> Signed-off-by: Evgeniy Baskov <baskov@...ras.ru>
>
> I'm not convinced about the use of the DXE services for this, and I
> think we should replace this patch with changes that base all the new
> protection code on the EFI memory attributes protocol only.
>
> We introduced that DXE code to remove protections from memory that was
> mapped read-only and/or non-executable, and described as such in the
> GCD memory map.
>
> Using it to manipulate restricted permissions like this is quite a
> different thing, and sadly (at least in EDK2), the GCD system memory
> map is not kept in sync with the updated permissions, i.e, the W^X
> protections for loaded images and the NX protection for arbitrary page
> allocations are both based on the PI CPU arch protocol, which
> manipulates the page tables directly, but does not record the modified
> attributes in the GCD or EFI memory maps, as this would result in
> massive fragmentation and break lots of other things.
>
> That means that, except for the specific use case for which we
> introduced the DXE services calls, the only reliable way to figure out
> what permission attributes a certain range of memory is using is the
> EFI memory attributes protocol, and I don't think we should use
> anything else for tightening down these protections.
>
>
Makes sense. I'll change the patch to only widen the permissions with
DXE, so it aligns with the original intention. And only apply stricter
permissions with memory attribute protocol.
Thanks!
>
>
>> ---
>> drivers/firmware/efi/libstub/mem.c | 168
>> ++++++++++++++++++------
>> drivers/firmware/efi/libstub/x86-stub.c | 17 ---
>> 2 files changed, 128 insertions(+), 57 deletions(-)
>>
>> diff --git a/drivers/firmware/efi/libstub/mem.c
>> b/drivers/firmware/efi/libstub/mem.c
>> index 3e47e5931f04..07d54c88c62e 100644
>> --- a/drivers/firmware/efi/libstub/mem.c
>> +++ b/drivers/firmware/efi/libstub/mem.c
>> @@ -5,6 +5,9 @@
>>
>> #include "efistub.h"
>>
>> +const efi_dxe_services_table_t *efi_dxe_table;
>> +efi_memory_attribute_protocol_t *efi_mem_attrib_proto;
>> +
>> /**
>> * efi_get_memory_map() - get memory map
>> * @map: pointer to memory map pointer to which to
>> assign the
>> @@ -129,66 +132,47 @@ void efi_free(unsigned long size, unsigned long
>> addr)
>> efi_bs_call(free_pages, addr, nr_pages);
>> }
>>
>> -/**
>> - * efi_adjust_memory_range_protection() - change memory range
>> protection attributes
>> - * @start: memory range start address
>> - * @size: memory range size
>> - *
>> - * Actual memory range for which memory attributes are modified is
>> - * the smallest ranged with start address and size aligned to
>> EFI_PAGE_SIZE
>> - * that includes [start, start + size].
>> - *
>> - * @return: status code
>> - */
>> -efi_status_t efi_adjust_memory_range_protection(unsigned long start,
>> - unsigned long size,
>> - unsigned long
>> attributes)
>> +static void retrieve_dxe_table(void)
>> +{
>> + efi_dxe_table =
>> get_efi_config_table(EFI_DXE_SERVICES_TABLE_GUID);
>> + if (efi_dxe_table &&
>> + efi_dxe_table->hdr.signature !=
>> EFI_DXE_SERVICES_TABLE_SIGNATURE) {
>> + efi_warn("Ignoring DXE services table: invalid
>> signature\n");
>> + efi_dxe_table = NULL;
>> + }
>> +}
>> +
>> +static efi_status_t adjust_mem_attrib_dxe(efi_physical_addr_t
>> rounded_start,
>> + efi_physical_addr_t
>> rounded_end,
>> + unsigned long attributes)
>> {
>> efi_status_t status;
>> efi_gcd_memory_space_desc_t desc;
>> - efi_physical_addr_t end, next;
>> - efi_physical_addr_t rounded_start, rounded_end;
>> + efi_physical_addr_t end, next, start;
>> efi_physical_addr_t unprotect_start, unprotect_size;
>>
>> - if (efi_dxe_table == NULL)
>> - return EFI_UNSUPPORTED;
>> + if (!efi_dxe_table) {
>> + retrieve_dxe_table();
>>
>> - /*
>> - * This function should not be used to modify attributes
>> - * other than writable/executable.
>> - */
>> -
>> - if ((attributes & ~(EFI_MEMORY_RO | EFI_MEMORY_XP)) != 0)
>> - return EFI_INVALID_PARAMETER;
>> -
>> - /*
>> - * Disallow simultaniously executable and writable memory
>> - * to inforce W^X policy if direct extraction code is enabled.
>> - */
>> -
>> - if ((attributes & (EFI_MEMORY_RO | EFI_MEMORY_XP)) == 0) {
>> - efi_warn("W^X violation at [%08lx,%08lx]\n",
>> - (unsigned long)rounded_start,
>> - (unsigned long)rounded_end);
>> + if (!efi_dxe_table)
>> + return EFI_UNSUPPORTED;
>> }
>>
>> - rounded_start = rounddown(start, EFI_PAGE_SIZE);
>> - rounded_end = roundup(start + size, EFI_PAGE_SIZE);
>> -
>> /*
>> * Don't modify memory region attributes, they are
>> * already suitable, to lower the possibility to
>> * encounter firmware bugs.
>> */
>>
>> - for (end = start + size; start < end; start = next) {
>> +
>> + for (start = rounded_start, end = rounded_end; start < end;
>> start = next) {
>>
>> status = efi_dxe_call(get_memory_space_descriptor,
>> start, &desc);
>>
>> if (status != EFI_SUCCESS) {
>> efi_warn("Unable to get memory descriptor at
>> %lx\n",
>> - start);
>> + (unsigned long)start);
>> return status;
>> }
>>
>> @@ -230,3 +214,107 @@ efi_status_t
>> efi_adjust_memory_range_protection(unsigned long start,
>>
>> return EFI_SUCCESS;
>> }
>> +
>> +static void retrieve_memory_attributes_proto(void)
>> +{
>> + efi_status_t status;
>> + efi_guid_t guid = EFI_MEMORY_ATTRIBUTE_PROTOCOL_GUID;
>> +
>> + status = efi_bs_call(locate_protocol, &guid, NULL,
>> + (void **)&efi_mem_attrib_proto);
>> + if (status != EFI_SUCCESS)
>> + efi_mem_attrib_proto = NULL;
>> +}
>> +
>> +/**
>> + * efi_adjust_memory_range_protection() - change memory range
>> protection attributes
>> + * @start: memory range start address
>> + * @size: memory range size
>> + *
>> + * Actual memory range for which memory attributes are modified is
>> + * the smallest ranged with start address and size aligned to
>> EFI_PAGE_SIZE
>> + * that includes [start, start + size].
>> + *
>> + * This function first attempts to use EFI_MEMORY_ATTRIBUTE_PROTOCOL,
>> + * that is a part of UEFI Specification since version 2.10.
>> + * If the protocol is unavailable it falls back to DXE services
>> functions.
>> + *
>> + * @return: status code
>> + */
>> +efi_status_t efi_adjust_memory_range_protection(unsigned long start,
>> + unsigned long size,
>> + unsigned long
>> attributes)
>> +{
>> + efi_status_t status;
>> + efi_physical_addr_t rounded_start, rounded_end;
>> + unsigned long attr_clear;
>> +
>> + /*
>> + * This function should not be used to modify attributes
>> + * other than writable/executable.
>> + */
>> +
>> + if ((attributes & ~(EFI_MEMORY_RO | EFI_MEMORY_XP)) != 0)
>> + return EFI_INVALID_PARAMETER;
>> +
>> + /*
>> + * Warn if requested to make memory simultaneously
>> + * executable and writable to enforce W^X policy.
>> + */
>> +
>> + if ((attributes & (EFI_MEMORY_RO | EFI_MEMORY_XP)) == 0) {
>> + efi_warn("W^X violation at [%08lx,%08lx]",
>> + (unsigned long)rounded_start,
>> + (unsigned long)rounded_end);
>> + }
>> +
>> + rounded_start = rounddown(start, EFI_PAGE_SIZE);
>> + rounded_end = roundup(start + size, EFI_PAGE_SIZE);
>> +
>> + if (!efi_mem_attrib_proto) {
>> + retrieve_memory_attributes_proto();
>> +
>> + /* Fall back to DXE services if unsupported */
>> + if (!efi_mem_attrib_proto) {
>> + return adjust_mem_attrib_dxe(rounded_start,
>> + rounded_end,
>> + attributes);
>> + }
>> + }
>> +
>> + /*
>> + * Unlike DXE services functions,
>> EFI_MEMORY_ATTRIBUTE_PROTOCOL
>> + * does not clear unset protection bit, so it needs to be
>> cleared
>> + * explcitly
>> + */
>> +
>> + attr_clear = ~attributes &
>> + (EFI_MEMORY_RO | EFI_MEMORY_XP | EFI_MEMORY_RP);
>> +
>> + status = efi_call_proto(efi_mem_attrib_proto,
>> + clear_memory_attributes,
>> + rounded_start,
>> + rounded_end - rounded_start,
>> + attr_clear);
>> + if (status != EFI_SUCCESS) {
>> + efi_warn("Failed to clear memory attributes at
>> [%08lx,%08lx]: %lx",
>> + (unsigned long)rounded_start,
>> + (unsigned long)rounded_end,
>> + status);
>> + return status;
>> + }
>> +
>> + status = efi_call_proto(efi_mem_attrib_proto,
>> + set_memory_attributes,
>> + rounded_start,
>> + rounded_end - rounded_start,
>> + attributes);
>> + if (status != EFI_SUCCESS) {
>> + efi_warn("Failed to set memory attributes at
>> [%08lx,%08lx]: %lx",
>> + (unsigned long)rounded_start,
>> + (unsigned long)rounded_end,
>> + status);
>> + }
>> +
>> + return status;
>> +}
>> diff --git a/drivers/firmware/efi/libstub/x86-stub.c
>> b/drivers/firmware/efi/libstub/x86-stub.c
>> index 60697fcd8950..06a62b121521 100644
>> --- a/drivers/firmware/efi/libstub/x86-stub.c
>> +++ b/drivers/firmware/efi/libstub/x86-stub.c
>> @@ -23,7 +23,6 @@
>> #define MAXMEM_X86_64_4LEVEL (1ull << 46)
>>
>> const efi_system_table_t *efi_system_table;
>> -const efi_dxe_services_table_t *efi_dxe_table;
>> u32 image_offset __section(".data");
>> static efi_loaded_image_t *image __section(".data");
>>
>> @@ -357,15 +356,6 @@ void __noreturn efi_exit(efi_handle_t handle,
>> efi_status_t status)
>> static void setup_sections_memory_protection(unsigned long
>> image_base)
>> {
>> #ifdef CONFIG_EFI_DXE_MEM_ATTRIBUTES
>> - efi_dxe_table =
>> get_efi_config_table(EFI_DXE_SERVICES_TABLE_GUID);
>> -
>> - if (!efi_dxe_table ||
>> - efi_dxe_table->hdr.signature !=
>> EFI_DXE_SERVICES_TABLE_SIGNATURE) {
>> - efi_warn("Unable to locate EFI DXE services table\n");
>> - efi_dxe_table = NULL;
>> - return;
>> - }
>> -
>> /* .setup [image_base, _head] */
>> efi_adjust_memory_range_protection(image_base,
>> (unsigned long)_head -
>> image_base,
>> @@ -732,13 +722,6 @@ asmlinkage unsigned long efi_main(efi_handle_t
>> handle,
>> if (efi_system_table->hdr.signature !=
>> EFI_SYSTEM_TABLE_SIGNATURE)
>> efi_exit(handle, EFI_INVALID_PARAMETER);
>>
>> - efi_dxe_table =
>> get_efi_config_table(EFI_DXE_SERVICES_TABLE_GUID);
>> - if (efi_dxe_table &&
>> - efi_dxe_table->hdr.signature !=
>> EFI_DXE_SERVICES_TABLE_SIGNATURE) {
>> - efi_warn("Ignoring DXE services table: invalid
>> signature\n");
>> - efi_dxe_table = NULL;
>> - }
>> -
>> setup_sections_memory_protection(bzimage_addr - image_offset);
>>
>> #ifdef CONFIG_CMDLINE_BOOL
>> --
>> 2.37.4
>>
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