diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
index d70c15de417b..2e9ee023e6bc 100644
--- a/arch/x86/purgatory/Makefile
+++ b/arch/x86/purgatory/Makefile
@@ -6,6 +6,9 @@ purgatory-y := purgatory.o stack.o setup-x86_$(BITS).o sha256.o entry64.o string
 targets += $(purgatory-y)
 PURGATORY_OBJS = $(addprefix $(obj)/,$(purgatory-y))
 
+$(obj)/sha256.o: $(srctree)/lib/sha256.c
+	$(call if_changed_rule,cc_o_c)
+
 LDFLAGS_purgatory.ro := -e purgatory_start -r --no-undefined -nostdlib -z nodefaultlib
 targets += purgatory.ro
 
diff --git a/arch/x86/purgatory/purgatory.c b/arch/x86/purgatory/purgatory.c
index 470edad96bb9..025c34ac0d84 100644
--- a/arch/x86/purgatory/purgatory.c
+++ b/arch/x86/purgatory/purgatory.c
@@ -11,9 +11,9 @@
  */
 
 #include <linux/bug.h>
+#include <linux/sha256.h>
 #include <asm/purgatory.h>
 
-#include "sha256.h"
 #include "../boot/string.h"
 
 unsigned long purgatory_backup_dest __section(.kexec-purgatory);
diff --git a/arch/x86/purgatory/string.c b/arch/x86/purgatory/string.c
index d886b1fa36f0..795ca4f2cb3c 100644
--- a/arch/x86/purgatory/string.c
+++ b/arch/x86/purgatory/string.c
@@ -10,4 +10,16 @@
  * Version 2.  See the file COPYING for more details.
  */
 
+#include <linux/types.h>
+
 #include "../boot/string.c"
+
+void *memcpy(void *dst, const void *src, size_t len)
+{
+	return __builtin_memcpy(dst, src, len);
+}
+
+void *memset(void *dst, int c, size_t len)
+{
+	return __builtin_memset(dst, c, len);
+}
diff --git a/arch/x86/purgatory/sha256.h b/include/linux/sha256.h
similarity index 62%
rename from arch/x86/purgatory/sha256.h
rename to include/linux/sha256.h
index 2867d9825a57..244fe01a65fb 100644
--- a/arch/x86/purgatory/sha256.h
+++ b/include/linux/sha256.h
@@ -13,9 +13,18 @@
 #include <linux/types.h>
 #include <crypto/sha.h>
 
+/*
+ * Stand-alone implementation of the SHA256 algorithm. It is designed to
+ * have as little dependencies as possible so it can be used in the
+ * kexec_file purgatory. In other cases you should use the implementation in
+ * crypto/.
+ *
+ * For details see lib/sha256.c
+ */
+
 extern int sha256_init(struct sha256_state *sctx);
 extern int sha256_update(struct sha256_state *sctx, const u8 *input,
-				unsigned int length);
+			 unsigned int length);
 extern int sha256_final(struct sha256_state *sctx, u8 *hash);
 
 #endif /* SHA256_H */
diff --git a/arch/x86/purgatory/sha256.c b/lib/sha256.c
similarity index 99%
rename from arch/x86/purgatory/sha256.c
rename to lib/sha256.c
index 548ca675a14a..4400c832e2aa 100644
--- a/arch/x86/purgatory/sha256.c
+++ b/lib/sha256.c
@@ -16,9 +16,9 @@
  */
 
 #include <linux/bitops.h>
+#include <linux/sha256.h>
+#include <linux/string.h>
 #include <asm/byteorder.h>
-#include "sha256.h"
-#include "../boot/string.h"
 
 static inline u32 Ch(u32 x, u32 y, u32 z)
 {