RISC-V: Add purgatory

This patch adds purgatory, the name and concept have been taken
from kexec-tools. Purgatory runs between two kernels, and do
verify sha256 hash to ensure the kernel to jump to is fine and
has not been corrupted after loading. Makefile is modified based
on x86 platform.

Signed-off-by: Li Zhengyu <lizhengyu3@huawei.com>
Link: https://lore.kernel.org/r/20220408100914.150110-6-lizhengyu3@huawei.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

4 files changed, 191 insertions, 0 deletions

diff --git a/arch/riscv/purgatory/.gitignore b/arch/riscv/purgatory/.gitignore
new file mode 100644
index 000000000000..38d7d1bda4d7
--- /dev/null
+++ b/arch/riscv/purgatory/.gitignore
@@ -0,0 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0-only
+purgatory.chk
+purgatory.ro
+kexec-purgatory.c
diff --git a/arch/riscv/purgatory/Makefile b/arch/riscv/purgatory/Makefile
new file mode 100644
index 000000000000..d4df200f7edf
--- /dev/null
+++ b/arch/riscv/purgatory/Makefile
@@ -0,0 +1,95 @@
+# SPDX-License-Identifier: GPL-2.0
+OBJECT_FILES_NON_STANDARD := y
+
+purgatory-y := purgatory.o sha256.o entry.o string.o ctype.o memcpy.o memset.o
+
+targets += $(purgatory-y)
+PURGATORY_OBJS = $(addprefix $(obj)/,$(purgatory-y))
+
+$(obj)/string.o: $(srctree)/lib/string.c FORCE
+	$(call if_changed_rule,cc_o_c)
+
+$(obj)/ctype.o: $(srctree)/lib/ctype.c FORCE
+	$(call if_changed_rule,cc_o_c)
+
+$(obj)/memcpy.o: $(srctree)/arch/riscv/lib/memcpy.S FORCE
+	$(call if_changed_rule,as_o_S)
+
+$(obj)/memset.o: $(srctree)/arch/riscv/lib/memset.S FORCE
+	$(call if_changed_rule,as_o_S)
+
+$(obj)/sha256.o: $(srctree)/lib/crypto/sha256.c FORCE
+	$(call if_changed_rule,cc_o_c)
+
+CFLAGS_sha256.o := -D__DISABLE_EXPORTS
+CFLAGS_string.o := -D__DISABLE_EXPORTS
+CFLAGS_ctype.o := -D__DISABLE_EXPORTS
+
+# When linking purgatory.ro with -r unresolved symbols are not checked,
+# also link a purgatory.chk binary without -r to check for unresolved symbols.
+PURGATORY_LDFLAGS := -e purgatory_start -z nodefaultlib
+LDFLAGS_purgatory.ro := -r $(PURGATORY_LDFLAGS)
+LDFLAGS_purgatory.chk := $(PURGATORY_LDFLAGS)
+targets += purgatory.ro purgatory.chk
+
+# Sanitizer, etc. runtimes are unavailable and cannot be linked here.
+GCOV_PROFILE	:= n
+KASAN_SANITIZE	:= n
+UBSAN_SANITIZE	:= n
+KCSAN_SANITIZE	:= n
+KCOV_INSTRUMENT := n
+
+# These are adjustments to the compiler flags used for objects that
+# make up the standalone purgatory.ro
+
+PURGATORY_CFLAGS_REMOVE := -mcmodel=kernel
+PURGATORY_CFLAGS := -mcmodel=medany -ffreestanding -fno-zero-initialized-in-bss
+PURGATORY_CFLAGS += $(DISABLE_STACKLEAK_PLUGIN) -DDISABLE_BRANCH_PROFILING
+PURGATORY_CFLAGS += -fno-stack-protector -g0
+
+# Default KBUILD_CFLAGS can have -pg option set when FTRACE is enabled. That
+# in turn leaves some undefined symbols like __fentry__ in purgatory and not
+# sure how to relocate those.
+ifdef CONFIG_FUNCTION_TRACER
+PURGATORY_CFLAGS_REMOVE		+= $(CC_FLAGS_FTRACE)
+endif
+
+ifdef CONFIG_STACKPROTECTOR
+PURGATORY_CFLAGS_REMOVE		+= -fstack-protector
+endif
+
+ifdef CONFIG_STACKPROTECTOR_STRONG
+PURGATORY_CFLAGS_REMOVE		+= -fstack-protector-strong
+endif
+
+CFLAGS_REMOVE_purgatory.o	+= $(PURGATORY_CFLAGS_REMOVE)
+CFLAGS_purgatory.o		+= $(PURGATORY_CFLAGS)
+
+CFLAGS_REMOVE_sha256.o		+= $(PURGATORY_CFLAGS_REMOVE)
+CFLAGS_sha256.o			+= $(PURGATORY_CFLAGS)
+
+CFLAGS_REMOVE_string.o		+= $(PURGATORY_CFLAGS_REMOVE)
+CFLAGS_string.o			+= $(PURGATORY_CFLAGS)
+
+CFLAGS_REMOVE_ctype.o		+= $(PURGATORY_CFLAGS_REMOVE)
+CFLAGS_ctype.o			+= $(PURGATORY_CFLAGS)
+
+AFLAGS_REMOVE_entry.o		+= -Wa,-gdwarf-2
+AFLAGS_REMOVE_memcpy.o		+= -Wa,-gdwarf-2
+AFLAGS_REMOVE_memset.o		+= -Wa,-gdwarf-2
+
+$(obj)/purgatory.ro: $(PURGATORY_OBJS) FORCE
+		$(call if_changed,ld)
+
+$(obj)/purgatory.chk: $(obj)/purgatory.ro FORCE
+		$(call if_changed,ld)
+
+targets += kexec-purgatory.c
+
+quiet_cmd_bin2c = BIN2C   $@
+      cmd_bin2c = $(objtree)/scripts/bin2c kexec_purgatory < $< > $@
+
+$(obj)/kexec-purgatory.c: $(obj)/purgatory.ro $(obj)/purgatory.chk FORCE
+	$(call if_changed,bin2c)
+
+obj-$(CONFIG_ARCH_HAS_KEXEC_PURGATORY)	+= kexec-purgatory.o
diff --git a/arch/riscv/purgatory/entry.S b/arch/riscv/purgatory/entry.S
new file mode 100644
index 000000000000..0194f4554130
--- /dev/null
+++ b/arch/riscv/purgatory/entry.S
@@ -0,0 +1,47 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * purgatory: Runs between two kernels
+ *
+ * Copyright (C) 2022 Huawei Technologies Co, Ltd.
+ *
+ * Author: Li Zhengyu (lizhengyu3@huawei.com)
+ *
+ */
+
+.macro	size, sym:req
+	.size \sym, . - \sym
+.endm
+
+.text
+
+.globl purgatory_start
+purgatory_start:
+
+	lla	sp, .Lstack
+	mv	s0, a0	/* The hartid of the current hart */
+	mv	s1, a1	/* Phys address of the FDT image */
+
+	jal	purgatory
+
+	/* Start new image. */
+	mv	a0, s0
+	mv	a1, s1
+	ld	a2, riscv_kernel_entry
+	jr	a2
+
+size purgatory_start
+
+.align 4
+	.rept	256
+	.quad	0
+	.endr
+.Lstack:
+
+.data
+
+.globl riscv_kernel_entry
+riscv_kernel_entry:
+	.quad	0
+size riscv_kernel_entry
+
+.end
diff --git a/arch/riscv/purgatory/purgatory.c b/arch/riscv/purgatory/purgatory.c
new file mode 100644
index 000000000000..80596ab5fb62
--- /dev/null
+++ b/arch/riscv/purgatory/purgatory.c
@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * purgatory: Runs between two kernels
+ *
+ * Copyright (C) 2022 Huawei Technologies Co, Ltd.
+ *
+ * Author: Li Zhengyu (lizhengyu3@huawei.com)
+ *
+ */
+
+#include <linux/purgatory.h>
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <asm/string.h>
+
+u8 purgatory_sha256_digest[SHA256_DIGEST_SIZE] __section(".kexec-purgatory");
+
+struct kexec_sha_region purgatory_sha_regions[KEXEC_SEGMENT_MAX] __section(".kexec-purgatory");
+
+static int verify_sha256_digest(void)
+{
+	struct kexec_sha_region *ptr, *end;
+	struct sha256_state ss;
+	u8 digest[SHA256_DIGEST_SIZE];
+
+	sha256_init(&ss);
+	end = purgatory_sha_regions + ARRAY_SIZE(purgatory_sha_regions);
+	for (ptr = purgatory_sha_regions; ptr < end; ptr++)
+		sha256_update(&ss, (uint8_t *)(ptr->start), ptr->len);
+	sha256_final(&ss, digest);
+	if (memcmp(digest, purgatory_sha256_digest, sizeof(digest)) != 0)
+		return 1;
+	return 0;
+}
+
+/* workaround for a warning with -Wmissing-prototypes */
+void purgatory(void);
+
+void purgatory(void)
+{
+	if (verify_sha256_digest())
+		for (;;)
+			/* loop forever */
+			;
+}