[PATCH] arm64: efi: Disable only the misbehaving runtime service on sync exceptions

[Ard Biesheuvel]

Alexandru reports that his Ampere Altra machine, whose buggy firmware
triggers a synchronous exception in its implementation of SetTime() when
called without SetVirtualAddressMap() having been called first, doesn't
quite recover from this, and starts spewing error messages into the log
that are unrelated to the buggy runtime service.

The driver in question is the EFI RTC driver, which should be fixed in
any case, as flooding the log like that (or doing any logging to the
kernel log at all on something whuch is not a severe issue) is not ok.

However, in this particular case, it would be beneficial for both
ordinary use as well as diagnostics regarding broken firmware if we only
prevent the broken runtime service from being called again, and permit
others (such as GetTime() which triggers the logging or the variable
services) from being used as normal.

So wire up the existing efi.runtime_supported_mask, and clear the
service's bit in the mask if the generic runtime service wrapper
observes a return value of EFI_ABORTED, which only happens if a service
call is aborted due to an exception. (EFI_ABORTED is not documented as a
valid error code for any of the EFI runtime services).

Cc: Alexandru Elisei <alexandru.elisei at arm.com>
Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
---
 arch/arm64/kernel/efi.c                 |  1 -
 arch/x86/platform/efi/quirks.c          |  2 +-
 drivers/firmware/efi/runtime-wrappers.c |  6 ++++--
 include/linux/efi.h                     | 24 ++++++++++++------------
 4 files changed, 17 insertions(+), 16 deletions(-)

diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c
index ee53f2a0aa03f54a..a3b8852f2698d9f7 100644
--- a/arch/arm64/kernel/efi.c
+++ b/arch/arm64/kernel/efi.c
@@ -153,7 +153,6 @@ asmlinkage efi_status_t __efi_rt_asm_recover(void);
 asmlinkage efi_status_t efi_handle_runtime_exception(const char *f)
 {
 	pr_err(FW_BUG "Synchronous exception occurred in EFI runtime service %s()\n", f);
-	clear_bit(EFI_RUNTIME_SERVICES, &efi.flags);
 	return EFI_ABORTED;
 }
 
diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
index b0b848d6933afbcf..3f48fdf42d97dc1f 100644
--- a/arch/x86/platform/efi/quirks.c
+++ b/arch/x86/platform/efi/quirks.c
@@ -757,9 +757,9 @@ void efi_crash_gracefully_on_page_fault(unsigned long phys_addr)
 
 	/* Signal error status to the efi caller process */
 	efi_rts_work.status = EFI_ABORTED;
+	efi.runtime_supported_mask = 0;
 	complete(&efi_rts_work.efi_rts_comp);
 
-	clear_bit(EFI_RUNTIME_SERVICES, &efi.flags);
 	pr_info("Froze efi_rts_wq and disabled EFI Runtime Services\n");
 
 	/*
diff --git a/drivers/firmware/efi/runtime-wrappers.c b/drivers/firmware/efi/runtime-wrappers.c
index f3e54f6616f02475..336b8bcec86d0127 100644
--- a/drivers/firmware/efi/runtime-wrappers.c
+++ b/drivers/firmware/efi/runtime-wrappers.c
@@ -60,8 +60,8 @@ struct efi_runtime_work efi_rts_work;
 ({									\
 	efi_rts_work.status = EFI_ABORTED;				\
 									\
-	if (!efi_enabled(EFI_RUNTIME_SERVICES)) {			\
-		pr_warn_once("EFI Runtime Services are disabled!\n");	\
+	if (!efi_rt_services_supported(efi_rts_work.efi_rts_id)) {	\
+		pr_warn_ratelimited("EFI Runtime Service is disabled!\n");\
 		goto exit;						\
 	}								\
 									\
@@ -83,6 +83,8 @@ struct efi_runtime_work efi_rts_work;
 	else								\
 		pr_err("Failed to queue work to efi_rts_wq.\n");	\
 									\
+	if (efi_rts_work.status == EFI_ABORTED)				\
+		efi.runtime_supported_mask &= ~efi_rts_work.efi_rts_id;	\
 exit:									\
 	efi_rts_work.efi_rts_id = EFI_NONE;				\
 	efi_rts_work.status;						\
diff --git a/include/linux/efi.h b/include/linux/efi.h
index 929d559ad41d29c6..61b252386d61cc4d 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -1254,18 +1254,18 @@ extern unsigned long rci2_table_phys;
  */
 enum efi_rts_ids {
 	EFI_NONE,
-	EFI_GET_TIME,
-	EFI_SET_TIME,
-	EFI_GET_WAKEUP_TIME,
-	EFI_SET_WAKEUP_TIME,
-	EFI_GET_VARIABLE,
-	EFI_GET_NEXT_VARIABLE,
-	EFI_SET_VARIABLE,
-	EFI_QUERY_VARIABLE_INFO,
-	EFI_GET_NEXT_HIGH_MONO_COUNT,
-	EFI_RESET_SYSTEM,
-	EFI_UPDATE_CAPSULE,
-	EFI_QUERY_CAPSULE_CAPS,
+	EFI_GET_TIME			= EFI_RT_SUPPORTED_GET_TIME,
+	EFI_SET_TIME			= EFI_RT_SUPPORTED_SET_TIME,
+	EFI_GET_WAKEUP_TIME		= EFI_RT_SUPPORTED_GET_WAKEUP_TIME,
+	EFI_SET_WAKEUP_TIME		= EFI_RT_SUPPORTED_SET_WAKEUP_TIME,
+	EFI_GET_VARIABLE		= EFI_RT_SUPPORTED_GET_VARIABLE,
+	EFI_GET_NEXT_VARIABLE		= EFI_RT_SUPPORTED_GET_NEXT_VARIABLE_NAME,
+	EFI_SET_VARIABLE		= EFI_RT_SUPPORTED_SET_VARIABLE,
+	EFI_GET_NEXT_HIGH_MONO_COUNT	= EFI_RT_SUPPORTED_GET_NEXT_HIGH_MONOTONIC_COUNT,
+	EFI_RESET_SYSTEM		= EFI_RT_SUPPORTED_RESET_SYSTEM,
+	EFI_UPDATE_CAPSULE		= EFI_RT_SUPPORTED_UPDATE_CAPSULE,
+	EFI_QUERY_CAPSULE_CAPS		= EFI_RT_SUPPORTED_QUERY_CAPSULE_CAPABILITIES,
+	EFI_QUERY_VARIABLE_INFO		= EFI_RT_SUPPORTED_QUERY_VARIABLE_INFO,
 };
 
 /*
-- 
2.35.1