From: Ard Biesheuvel <ardb@kernel.org>
Date: Wed, 8 Jul 2020 13:01:57 +0300
Subject: efi/efivars: Expose RT service availability via efivars abstraction
Patch-mainline: v5.8-rc7
Git-commit: f88814cc2578c121e6edef686365036db72af0ed
References: bsc#1174029, bsc#1174110, bsc#1174111

Commit

  bf67fad19e493b ("efi: Use more granular check for availability for variable services")

introduced a check into the efivarfs, efi-pstore and other drivers that
aborts loading of the module if not all three variable runtime services
(GetVariable, SetVariable and GetNextVariable) are supported. However, this
results in efivarfs being unavailable entirely if only SetVariable support
is missing, which is only needed if you want to make any modifications.
Also, efi-pstore and the sysfs EFI variable interface could be backed by
another implementation of the 'efivars' abstraction, in which case it is
completely irrelevant which services are supported by the EFI firmware.

So make the generic 'efivars' abstraction dependent on the availibility of
the GetVariable and GetNextVariable EFI runtime services, and add a helper
'efivar_supports_writes()' to find out whether the currently active efivars
abstraction supports writes (and wire it up to the availability of
SetVariable for the generic one).

Then, use the efivar_supports_writes() helper to decide whether to permit
efivarfs to be mounted read-write, and whether to enable efi-pstore or the
sysfs EFI variable interface altogether.

Fixes: bf67fad19e493b ("efi: Use more granular check for availability for variable services")
Reported-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Acked-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Tested-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Lee, Chun-Yi <jlee@suse.com>
---
 drivers/firmware/efi/efi-pstore.c |    5 +----
 drivers/firmware/efi/efi.c        |   12 ++++++++----
 drivers/firmware/efi/efivars.c    |    5 +----
 drivers/firmware/efi/vars.c       |    6 ++++++
 fs/efivarfs/super.c               |    6 +++---
 include/linux/efi.h               |    1 +
 6 files changed, 20 insertions(+), 15 deletions(-)

--- a/drivers/firmware/efi/efi-pstore.c
+++ b/drivers/firmware/efi/efi-pstore.c
@@ -356,10 +356,7 @@ static struct pstore_info efi_pstore_inf
 
 static __init int efivars_pstore_init(void)
 {
-	if (!efi_rt_services_supported(EFI_RT_SUPPORTED_VARIABLE_SERVICES))
-		return 0;
-
-	if (!efivars_kobject())
+	if (!efivars_kobject() || !efivar_supports_writes())
 		return 0;
 
 	if (efivars_pstore_disable)
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -209,11 +209,13 @@ static struct efivar_operations generic_
 static int generic_ops_register(void)
 {
 	generic_ops.get_variable = efi.get_variable;
-	generic_ops.set_variable = efi.set_variable;
-	generic_ops.set_variable_nonblocking = efi.set_variable_nonblocking;
 	generic_ops.get_next_variable = efi.get_next_variable;
 	generic_ops.query_variable_store = efi_query_variable_store;
 
+	if (efi_rt_services_supported(EFI_RT_SUPPORTED_SET_VARIABLE)) {
+		generic_ops.set_variable = efi.set_variable;
+		generic_ops.set_variable_nonblocking = efi.set_variable_nonblocking;
+	}
 	return efivars_register(&generic_efivars, &generic_ops, efi_kobj);
 }
 
@@ -362,7 +364,8 @@ static int __init efisubsys_init(void)
 		return -ENOMEM;
 	}
 
-	if (efi_rt_services_supported(EFI_RT_SUPPORTED_VARIABLE_SERVICES)) {
+	if (efi_rt_services_supported(EFI_RT_SUPPORTED_GET_VARIABLE |
+				      EFI_RT_SUPPORTED_GET_NEXT_VARIABLE_NAME)) {
 		efivar_ssdt_load();
 		error = generic_ops_register();
 		if (error)
@@ -393,7 +396,8 @@ static int __init efisubsys_init(void)
 err_remove_group:
 	sysfs_remove_group(efi_kobj, &efi_subsys_attr_group);
 err_unregister:
-	if (efi_rt_services_supported(EFI_RT_SUPPORTED_VARIABLE_SERVICES))
+	if (efi_rt_services_supported(EFI_RT_SUPPORTED_GET_VARIABLE |
+				      EFI_RT_SUPPORTED_GET_NEXT_VARIABLE_NAME))
 		generic_ops_unregister();
 err_put:
 	kobject_put(efi_kobj);
--- a/drivers/firmware/efi/efivars.c
+++ b/drivers/firmware/efi/efivars.c
@@ -680,11 +680,8 @@ int efivars_sysfs_init(void)
 	struct kobject *parent_kobj = efivars_kobject();
 	int error = 0;
 
-	if (!efi_rt_services_supported(EFI_RT_SUPPORTED_VARIABLE_SERVICES))
-		return -ENODEV;
-
 	/* No efivars has been registered yet */
-	if (!parent_kobj)
+	if (!parent_kobj || !efivar_supports_writes())
 		return 0;
 
 	printk(KERN_INFO "EFI Variables Facility v%s %s\n", EFIVARS_VERSION,
--- a/drivers/firmware/efi/vars.c
+++ b/drivers/firmware/efi/vars.c
@@ -1229,3 +1229,9 @@ out:
 	return rv;
 }
 EXPORT_SYMBOL_GPL(efivars_unregister);
+
+int efivar_supports_writes(void)
+{
+	return __efivars && __efivars->ops->set_variable;
+}
+EXPORT_SYMBOL_GPL(efivar_supports_writes);
--- a/fs/efivarfs/super.c
+++ b/fs/efivarfs/super.c
@@ -201,6 +201,9 @@ static int efivarfs_fill_super(struct su
 	sb->s_d_op		= &efivarfs_d_ops;
 	sb->s_time_gran         = 1;
 
+	if (!efivar_supports_writes())
+		sb->s_flags |= SB_RDONLY;
+
 	inode = efivarfs_get_inode(sb, NULL, S_IFDIR | 0755, 0, true);
 	if (!inode)
 		return -ENOMEM;
@@ -252,9 +255,6 @@ static struct file_system_type efivarfs_
 
 static __init int efivarfs_init(void)
 {
-	if (!efi_rt_services_supported(EFI_RT_SUPPORTED_VARIABLE_SERVICES))
-		return -ENODEV;
-
 	if (!efivars_kobject())
 		return -ENODEV;
 
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -1525,6 +1525,7 @@ int efivars_register(struct efivars *efi
 int efivars_unregister(struct efivars *efivars);
 struct kobject *efivars_kobject(void);
 
+int efivar_supports_writes(void);
 int efivar_init(int (*func)(efi_char16_t *, efi_guid_t, unsigned long, void *),
 		void *data, bool duplicates, struct list_head *head);