arm64: efi: Force the use of SetVirtualAddressMap() on Altra machines

Ampere Altra machines are reported to misbehave when the SetTime() EFI
runtime service is called after ExitBootServices() but before calling
SetVirtualAddressMap(). Given that the latter is horrid, pointless and
explicitly documented as optional by the EFI spec, we no longer invoke
it at boot if the configured size of the VA space guarantees that the
EFI runtime memory regions can remain mapped 1:1 like they are at boot
time.

On Ampere Altra machines, this results in SetTime() calls issued by the
rtc-efi driver triggering synchronous exceptions during boot.  We can
now recover from those without bringing down the system entirely, due to
commit 23715a26c8d81291 ("arm64: efi: Recover from synchronous
exceptions occurring in firmware"). However, it would be better to avoid
the issue entirely, given that the firmware appears to remain in a funny
state after this.

So attempt to identify these machines based on the 'family' field in the
type #1 SMBIOS record, and call SetVirtualAddressMap() unconditionally
in that case.

Tested-by: Alexandru Elisei <alexandru.elisei@gmail.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

4 files changed, 93 insertions, 2 deletions

diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
index b1601aad7e1a..ef5045a53ce0 100644
--- a/drivers/firmware/efi/libstub/Makefile
+++ b/drivers/firmware/efi/libstub/Makefile
@@ -82,7 +82,7 @@ $(obj)/lib-%.o: $(srctree)/lib/%.c FORCE
 lib-$(CONFIG_EFI_GENERIC_STUB)	+= efi-stub.o string.o intrinsics.o systable.o
 
 lib-$(CONFIG_ARM)		+= arm32-stub.o
-lib-$(CONFIG_ARM64)		+= arm64-stub.o
+lib-$(CONFIG_ARM64)		+= arm64-stub.o smbios.o
 lib-$(CONFIG_X86)		+= x86-stub.o
 lib-$(CONFIG_RISCV)		+= riscv-stub.o
 lib-$(CONFIG_LOONGARCH)		+= loongarch-stub.o
diff --git a/drivers/firmware/efi/libstub/arm64-stub.c b/drivers/firmware/efi/libstub/arm64-stub.c
index 259e4b852d63..f9de5217ea65 100644
--- a/drivers/firmware/efi/libstub/arm64-stub.c
+++ b/drivers/firmware/efi/libstub/arm64-stub.c
@@ -15,6 +15,21 @@
 
 #include "efistub.h"
 
+static bool system_needs_vamap(void)
+{
+	const u8 *type1_family = efi_get_smbios_string(1, family);
+
+	/*
+	 * Ampere Altra machines crash in SetTime() if SetVirtualAddressMap()
+	 * has not been called prior.
+	 */
+	if (!type1_family || strcmp(type1_family, "Altra"))
+		return false;
+
+	efi_warn("Working around broken SetVirtualAddressMap()\n");
+	return true;
+}
+
 efi_status_t check_platform_features(void)
 {
 	u64 tg;
@@ -24,7 +39,7 @@ efi_status_t check_platform_features(void)
 	 * UEFI runtime regions 1:1 and so calling SetVirtualAddressMap() is
 	 * unnecessary.
 	 */
-	if (VA_BITS_MIN >= 48)
+	if (VA_BITS_MIN >= 48 && !system_needs_vamap())
 		efi_novamap = true;
 
 	/* UEFI mandates support for 4 KB granularity, no need to check */
diff --git a/drivers/firmware/efi/libstub/efistub.h b/drivers/firmware/efi/libstub/efistub.h
index a30fb5d8ef05..eb03d5a9aac8 100644
--- a/drivers/firmware/efi/libstub/efistub.h
+++ b/drivers/firmware/efi/libstub/efistub.h
@@ -975,4 +975,32 @@ efi_enable_reset_attack_mitigation(void) { }
 
 void efi_retrieve_tpm2_eventlog(void);
 
+struct efi_smbios_record {
+	u8	type;
+	u8	length;
+	u16	handle;
+};
+
+struct efi_smbios_type1_record {
+	struct efi_smbios_record	header;
+
+	u8				manufacturer;
+	u8				product_name;
+	u8				version;
+	u8				serial_number;
+	efi_guid_t			uuid;
+	u8				wakeup_type;
+	u8				sku_number;
+	u8				family;
+};
+
+#define efi_get_smbios_string(__type, __name) ({			\
+	int size = sizeof(struct efi_smbios_type ## __type ## _record);	\
+	int off = offsetof(struct efi_smbios_type ## __type ## _record,	\
+			   __name);					\
+	__efi_get_smbios_string(__type, off, size);			\
+})
+
+const u8 *__efi_get_smbios_string(u8 type, int offset, int recsize);
+
 #endif
diff --git a/drivers/firmware/efi/libstub/smbios.c b/drivers/firmware/efi/libstub/smbios.c
new file mode 100644
index 000000000000..460418b7f5f5
--- /dev/null
+++ b/drivers/firmware/efi/libstub/smbios.c
@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: GPL-2.0-only
+// Copyright 2022 Google LLC
+// Author: Ard Biesheuvel <ardb@google.com>
+
+#include <linux/efi.h>
+
+#include "efistub.h"
+
+typedef struct efi_smbios_protocol efi_smbios_protocol_t;
+
+struct efi_smbios_protocol {
+	efi_status_t (__efiapi *add)(efi_smbios_protocol_t *, efi_handle_t,
+				     u16 *, struct efi_smbios_record *);
+	efi_status_t (__efiapi *update_string)(efi_smbios_protocol_t *, u16 *,
+					       unsigned long *, u8 *);
+	efi_status_t (__efiapi *remove)(efi_smbios_protocol_t *, u16);
+	efi_status_t (__efiapi *get_next)(efi_smbios_protocol_t *, u16 *, u8 *,
+					  struct efi_smbios_record **,
+					  efi_handle_t *);
+
+	u8 major_version;
+	u8 minor_version;
+};
+
+const u8 *__efi_get_smbios_string(u8 type, int offset, int recsize)
+{
+	struct efi_smbios_record *record;
+	efi_smbios_protocol_t *smbios;
+	efi_status_t status;
+	u16 handle = 0xfffe;
+	const u8 *strtable;
+
+	status = efi_bs_call(locate_protocol, &EFI_SMBIOS_PROTOCOL_GUID, NULL,
+			     (void **)&smbios) ?:
+		 efi_call_proto(smbios, get_next, &handle, &type, &record, NULL);
+	if (status != EFI_SUCCESS)
+		return NULL;
+
+	strtable = (u8 *)record + recsize;
+	for (int i = 1; i < ((u8 *)record)[offset]; i++) {
+		int len = strlen(strtable);
+
+		if (!len)
+			return NULL;
+		strtable += len + 1;
+	}
+	return strtable;
+}