[PATCH v2] x86/efi: Safely enable unaccepted memory in UEFI

[Dionna Glaze]

This patch depends on Kirill A. Shutemov's series

[PATCHv8 00/14] mm, x86/cc: Implement support for unaccepted memory

The UEFI v2.9 specification includes a new memory type to be used in
environments where the OS must accept memory that is provided from its
host. Before the introduction of this memory type, all memory was
accepted eagerly in the firmware. In order for the firmware to safely
stop accepting memory on the OS's behalf, the OS must affirmatively
indicate support to the firmware.

Enabling unaccepted memory requires calling a 0-argument enablement
protocol before ExitBootServices. This call is only made if the kernel
is compiled with UNACCEPTED_MEMORY=y

The naming of the protocol guid is dependent on the standardization of
the protocol, which is being discussed. Acceptance is contingent on
the kernel community's approval.

Cc: Ard Biescheuvel <ardb@xxxxxxxxxx>
Cc: "Min M. Xu" <min.m.xu@xxxxxxxxx>
Cc: Gerd Hoffmann <kraxel@xxxxxxxxxx>
Cc: James Bottomley <jejb@xxxxxxxxxxxxx>
Cc: Tom Lendacky <Thomas.Lendacky@xxxxxxx>
Cc: Jiewen Yao <jiewen.yao@xxxxxxxxx>
Cc: Erdem Aktas <erdemaktas@xxxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>

Signed-off-by: Dionna Glaze <dionnaglaze@xxxxxxxxxx>
---
 drivers/firmware/efi/libstub/x86-stub.c | 37 +++++++++++++++++++++++++
 include/linux/efi.h                     |  1 +
 2 files changed, 38 insertions(+)

diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
index a0bfd31358ba..abf31e5ade55 100644
--- a/drivers/firmware/efi/libstub/x86-stub.c
+++ b/drivers/firmware/efi/libstub/x86-stub.c
@@ -26,6 +26,17 @@ const efi_dxe_services_table_t *efi_dxe_table;
 u32 image_offset __section(".data");
 static efi_loaded_image_t *image = NULL;
 
+typedef union memory_acceptance_protocol memory_acceptance_protocol_t;
+union memory_acceptance_protocol {
+	struct {
+		efi_status_t (__efiapi *allow_unaccepted_memory)(
+			memory_acceptance_protocol_t *);
+	};
+	struct {
+		u32 allow_unaccepted_memory;
+	} mixed_mode;
+};
+
 static efi_status_t
 preserve_pci_rom_image(efi_pci_io_protocol_t *pci, struct pci_setup_rom **__rom)
 {
@@ -310,6 +321,30 @@ setup_memory_protection(unsigned long image_base, unsigned long image_size)
 #endif
 }
 
+
+static void setup_unaccepted_memory(void)
+{
+	efi_guid_t mem_acceptance_proto = EFI_MEMORY_ACCEPTANCE_PROTOCOL_GUID;
+	memory_acceptance_protocol_t *proto;
+	efi_status_t status;
+
+	if (!IS_ENABLED(CONFIG_UNACCEPTED_MEMORY))
+		return;
+
+	/*
+	 * Enable unaccepted memory before calling exit boot services in order
+	 * for the UEFI to not accept all memory on EBS.
+	 */
+	status = efi_bs_call(locate_protocol, &mem_acceptance_proto, NULL,
+			     (void **)&proto);
+	if (status != EFI_SUCCESS)
+		return;
+
+	status = efi_call_proto(proto, allow_unaccepted_memory);
+	if (status != EFI_SUCCESS)
+		efi_err("Memory acceptance protocol failed\n");
+}
+
 static const efi_char16_t apple[] = L"Apple";
 
 static void setup_quirks(struct boot_params *boot_params,
@@ -899,6 +934,8 @@ asmlinkage unsigned long efi_main(efi_handle_t handle,
 
 	setup_quirks(boot_params, bzimage_addr, buffer_end - buffer_start);
 
+	setup_unaccepted_memory();
+
 	status = exit_boot(boot_params, handle);
 	if (status != EFI_SUCCESS) {
 		efi_err("exit_boot() failed!\n");
diff --git a/include/linux/efi.h b/include/linux/efi.h
index 4b27519143f5..bfc0e4f2aba5 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -391,6 +391,7 @@ void efi_native_runtime_setup(void);
 #define EFI_RT_PROPERTIES_TABLE_GUID		EFI_GUID(0xeb66918a, 0x7eef, 0x402a,  0x84, 0x2e, 0x93, 0x1d, 0x21, 0xc3, 0x8a, 0xe9)
 #define EFI_DXE_SERVICES_TABLE_GUID		EFI_GUID(0x05ad34ba, 0x6f02, 0x4214,  0x95, 0x2e, 0x4d, 0xa0, 0x39, 0x8e, 0x2b, 0xb9)
 #define EFI_SMBIOS_PROTOCOL_GUID		EFI_GUID(0x03583ff6, 0xcb36, 0x4940,  0x94, 0x7e, 0xb9, 0xb3, 0x9f, 0x4a, 0xfa, 0xf7)
+#define EFI_MEMORY_ACCEPTANCE_PROTOCOL_GUID	EFI_GUID(0xc5a010fe, 0x38a7, 0x4531,  0x8a, 0x4a, 0x05, 0x00, 0xd2, 0xfd, 0x16, 0x49)
 
 #define EFI_IMAGE_SECURITY_DATABASE_GUID	EFI_GUID(0xd719b2cb, 0x3d3a, 0x4596,  0xa3, 0xbc, 0xda, 0xd0, 0x0e, 0x67, 0x65, 0x6f)
 #define EFI_SHIM_LOCK_GUID			EFI_GUID(0x605dab50, 0xe046, 0x4300,  0xab, 0xb6, 0x3d, 0xd8, 0x10, 0xdd, 0x8b, 0x23)
-- 
2.39.0.314.g84b9a713c41-goog