efi/x86: Align GUIDs to their size in the mixed mode runtime wrapper

Hans reports that his mixed mode systems running v5.6-rc1 kernels hit
the WARN_ON() in virt_to_phys_or_null_size(), caused by the fact that
efi_guid_t objects on the vmap'ed stack happen to be misaligned with
respect to their sizes. As a quick (i.e., backportable) fix, copy GUID
pointer arguments to the local stack into a buffer that is naturally
aligned to its size, so that it is guaranteed to cover only one
physical page.

Note that on x86, we cannot rely on the stack pointer being aligned
the way the compiler expects, so we need to allocate an 8-byte aligned
buffer of sufficient size, and copy the GUID into that buffer at an
offset that is aligned to 16 bytes.

Fixes: f6697df ("x86/efi: Prevent mixed mode boot corruption with CONFIG_VMAP_STACK=y")
Reported-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Hans de Goede <hdegoede@redhat.com>
Cc: linux-efi@vger.kernel.org
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20200221084849.26878-2-ardb@kernel.org

arch/x86/platform/efi/efi_64.c

@@ -658,15 +658,19 @@ static efi_status_t
 efi_thunk_get_variable(efi_char16_t *name, efi_guid_t *vendor,
 		       u32 *attr, unsigned long *data_size, void *data)
 {
+	u8 buf[24] __aligned(8);
+	efi_guid_t *vnd = PTR_ALIGN((efi_guid_t *)buf, sizeof(*vnd));
 	efi_status_t status;
 	u32 phys_name, phys_vendor, phys_attr;
 	u32 phys_data_size, phys_data;
 	unsigned long flags;
 
 	spin_lock_irqsave(&efi_runtime_lock, flags);
 
+	*vnd = *vendor;
+
 	phys_data_size = virt_to_phys_or_null(data_size);
-	phys_vendor = virt_to_phys_or_null(vendor);
+	phys_vendor = virt_to_phys_or_null(vnd);
 	phys_name = virt_to_phys_or_null_size(name, efi_name_size(name));
 	phys_attr = virt_to_phys_or_null(attr);
 	phys_data = virt_to_phys_or_null_size(data, *data_size);
@@ -683,14 +687,18 @@ static efi_status_t
 efi_thunk_set_variable(efi_char16_t *name, efi_guid_t *vendor,
 		       u32 attr, unsigned long data_size, void *data)
 {
+	u8 buf[24] __aligned(8);
+	efi_guid_t *vnd = PTR_ALIGN((efi_guid_t *)buf, sizeof(*vnd));
 	u32 phys_name, phys_vendor, phys_data;
 	efi_status_t status;
 	unsigned long flags;
 
 	spin_lock_irqsave(&efi_runtime_lock, flags);
 
+	*vnd = *vendor;
+
 	phys_name = virt_to_phys_or_null_size(name, efi_name_size(name));
-	phys_vendor = virt_to_phys_or_null(vendor);
+	phys_vendor = virt_to_phys_or_null(vnd);
 	phys_data = virt_to_phys_or_null_size(data, data_size);
 
 	/* If data_size is > sizeof(u32) we've got problems */
@@ -707,15 +715,19 @@ efi_thunk_set_variable_nonblocking(efi_char16_t *name, efi_guid_t *vendor,
 				   u32 attr, unsigned long data_size,
 				   void *data)
 {
+	u8 buf[24] __aligned(8);
+	efi_guid_t *vnd = PTR_ALIGN((efi_guid_t *)buf, sizeof(*vnd));
 	u32 phys_name, phys_vendor, phys_data;
 	efi_status_t status;
 	unsigned long flags;
 
 	if (!spin_trylock_irqsave(&efi_runtime_lock, flags))
 		return EFI_NOT_READY;
 
+	*vnd = *vendor;
+
 	phys_name = virt_to_phys_or_null_size(name, efi_name_size(name));
-	phys_vendor = virt_to_phys_or_null(vendor);
+	phys_vendor = virt_to_phys_or_null(vnd);
 	phys_data = virt_to_phys_or_null_size(data, data_size);
 
 	/* If data_size is > sizeof(u32) we've got problems */
@@ -732,21 +744,26 @@ efi_thunk_get_next_variable(unsigned long *name_size,
 			    efi_char16_t *name,
 			    efi_guid_t *vendor)
 {
+	u8 buf[24] __aligned(8);
+	efi_guid_t *vnd = PTR_ALIGN((efi_guid_t *)buf, sizeof(*vnd));
 	efi_status_t status;
 	u32 phys_name_size, phys_name, phys_vendor;
 	unsigned long flags;
 
 	spin_lock_irqsave(&efi_runtime_lock, flags);
 
+	*vnd = *vendor;
+
 	phys_name_size = virt_to_phys_or_null(name_size);
-	phys_vendor = virt_to_phys_or_null(vendor);
+	phys_vendor = virt_to_phys_or_null(vnd);
 	phys_name = virt_to_phys_or_null_size(name, *name_size);
 
 	status = efi_thunk(get_next_variable, phys_name_size,
 			   phys_name, phys_vendor);
 
 	spin_unlock_irqrestore(&efi_runtime_lock, flags);
 
+	*vendor = *vnd;
 	return status;
 }