efi: capsule: clean scatter-gather entries from the D-cache

Scatter-gather lists passed to UpdateCapsule() should be cleaned
from the D-cache to ensure that they are visible to the CPU after a
warm reboot before the MMU is enabled. On ARM and arm64 systems, this
implies a D-cache clean by virtual address to the point of coherency.

However, due to the fact that the firmware itself is not able to map
physical addresses back to virtual addresses when running under the OS,
this must be done by the caller.

Signed-off-by: Ard Biesheuvel <[e-mail]>

arch/arm/include/asm/efi.h

···
 	u32	sctlr_after_ebs;
 };
 
+static inline void efi_capsule_flush_cache_range(void *addr, int size)
+{
+	__cpuc_flush_dcache_area(addr, size);
+}
+
 #endif /* _ASM_ARM_EFI_H */

arch/arm64/include/asm/efi.h

···
 void efi_virtmap_load(void);
 void efi_virtmap_unload(void);
 
+static inline void efi_capsule_flush_cache_range(void *addr, int size)
+{
+	__flush_dcache_area(addr, size);
+}
+
 #endif /* _ASM_EFI_H */

drivers/firmware/efi/capsule.c

···
 #include <linux/highmem.h>
 #include <linux/efi.h>
 #include <linux/vmalloc.h>
+#include <asm/efi.h>
 #include <asm/io.h>
 
 typedef struct {
···
 		else
 			sglist[j].data = page_to_phys(sg_pages[i + 1]);
 
+#if defined(CONFIG_ARM) || defined(CONFIG_ARM64)
+		/*
+		 * At runtime, the firmware has no way to find out where the
+		 * sglist elements are mapped, if they are mapped in the first
+		 * place. Therefore, on architectures that can only perform
+		 * cache maintenance by virtual address, the firmware is unable
+		 * to perform this maintenance, and so it is up to the OS to do
+		 * it instead.
+		 */
+		efi_capsule_flush_cache_range(sglist, PAGE_SIZE);
+#endif
 		kunmap_atomic(sglist);
 	}