riscv: kexec: add kexec_file_load() support

This patch set implements kexec_file_load() for RISC-V, which is
currently only allowed on rv64 due to some minor build issues on 32-bit
platforms in the generic code.  This allows users to kexec() using an FD
as opposed to a buffer.

Link: https://lore.kernel.org/all/20220408100914.150110-1-lizhengyu3@huawei.com/

* palmer/riscv-kexec_file:
  RISC-V: Load purgatory in kexec_file
  RISC-V: Add purgatory
  RISC-V: Support for kexec_file on panic
  RISC-V: Add kexec_file support
  RISC-V: use memcpy for kexec_file mode
  kexec_file: Fix kexec_file.c build error for riscv platform

Author: palmer-dabbelt

arch/riscv/Kbuild

@@ -3,5 +3,7 @@
 obj-y += kernel/ mm/ net/
 obj-$(CONFIG_BUILTIN_DTB) += boot/dts/
 
+obj-$(CONFIG_ARCH_HAS_KEXEC_PURGATORY) += purgatory/
+
 # for cleaning
 subdir- += boot

arch/riscv/Kconfig

@@ -418,6 +418,26 @@ config KEXEC
 
 	  The name comes from the similarity to the exec system call.
 
+config KEXEC_FILE
+	bool "kexec file based systmem call"
+	select KEXEC_CORE
+	select KEXEC_ELF
+	select HAVE_IMA_KEXEC if IMA
+	depends on 64BIT
+	help
+	  This is new version of kexec system call. This system call is
+	  file based and takes file descriptors as system call argument
+	  for kernel and initramfs as opposed to list of segments as
+	  accepted by previous system call.
+
+	  If you don't know what to do here, say Y.
+
+config ARCH_HAS_KEXEC_PURGATORY
+	def_bool KEXEC_FILE
+	select BUILD_BIN2C
+	depends on CRYPTO=y
+	depends on CRYPTO_SHA256=y
+
 config CRASH_DUMP
 	bool "Build kdump crash kernel"
 	help

arch/riscv/include/asm/kexec.h

@@ -53,4 +53,8 @@ typedef void (*riscv_kexec_method)(unsigned long first_ind_entry,
 
 extern riscv_kexec_method riscv_kexec_norelocate;
 
+#ifdef CONFIG_KEXEC_FILE
+extern const struct kexec_file_ops elf_kexec_ops;
+#endif
+
 #endif

arch/riscv/kernel/Makefile

@@ -79,6 +79,7 @@ endif
 obj-$(CONFIG_HOTPLUG_CPU)	+= cpu-hotplug.o
 obj-$(CONFIG_KGDB)		+= kgdb.o
 obj-$(CONFIG_KEXEC)		+= kexec_relocate.o crash_save_regs.o machine_kexec.o
+obj-$(CONFIG_KEXEC_FILE)	+= elf_kexec.o machine_kexec_file.o
 obj-$(CONFIG_CRASH_DUMP)	+= crash_dump.o
 
 obj-$(CONFIG_JUMP_LABEL)	+= jump_label.o