kexec: Introduce a bpf-prog lskel to parse PE file

Analague to kernel/bpf/preload/iterators/Makefile,
this Makefile is not invoked by the Kbuild system. It needs to be
invoked manually when kexec_pe_parser_bpf.c is changed so that
kexec_pe_parser_bpf.lskel.h can be re-generated by the command "bpftool
gen skeleton -L kexec_pe_parser_bpf.o".

kexec_pe_parser_bpf.lskel.h is used directly by the kernel kexec code in
later patch. For this patch, there are bpf bytecode contained in
opts_data[] and opts_insn[] in kexec_pe_parser_bpf.lskel.h, but in the
following patch, they will be removed and only the function API in
kexec_pe_parser_bpf.lskel.h left.

As exposed in kexec_pe_parser_bpf.lskel.h, the interface between
bpf-prog and the kernel are constituted by:

four maps:
                struct bpf_map_desc ringbuf_1;
                struct bpf_map_desc ringbuf_2;
                struct bpf_map_desc ringbuf_3;
                struct bpf_map_desc ringbuf_4;
four sections:
                struct bpf_map_desc rodata;
                struct bpf_map_desc data;
                struct bpf_map_desc bss;
                struct bpf_map_desc rodata_str1_1;

two progs:
        SEC("fentry.s/bpf_handle_pefile")
        SEC("fentry.s/bpf_post_handle_pefile")

They are fixed and provided for all kinds of bpf-prog which interacts
with the kexec kernel component.

Signed-off-by: Pingfan Liu <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Cc: Baoquan He <[email protected]>
Cc: Dave Young <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Philipp Rudo <[email protected]>
Cc: [email protected]
To: [email protected]

Author: Pingfan Liu

kernel/kexec_bpf/Makefile

@@ -0,0 +1,63 @@
+# SPDX-License-Identifier: GPL-2.0
+OUTPUT := .output
+CLANG ?= clang
+LLC ?= llc
+LLVM_STRIP ?= llvm-strip
+DEFAULT_BPFTOOL := $(OUTPUT)/sbin/bpftool
+BPFTOOL ?= $(DEFAULT_BPFTOOL)
+LIBBPF_SRC := $(abspath ../../tools/lib/bpf)
+BPFOBJ := $(OUTPUT)/libbpf.a
+BPF_INCLUDE := $(OUTPUT)
+INCLUDES := -I$(OUTPUT) -I$(BPF_INCLUDE) -I$(abspath ../../tools/lib)        \
+       -I$(abspath ../../tools/include/uapi)
+CFLAGS := -g -Wall
+
+srctree := $(patsubst %/kernel/kexec_bpf,%,$(CURDIR))
+VMLINUX = $(srctree)/vmlinux
+
+abs_out := $(abspath $(OUTPUT))
+ifeq ($(V),1)
+Q =
+msg =
+else
+Q = @
+msg = @printf '  %-8s %s%s\n' "$(1)" "$(notdir $(2))" "$(if $(3), $(3))";
+MAKEFLAGS += --no-print-directory
+submake_extras := feature_display=0
+endif
+
+.DELETE_ON_ERROR:
+
+.PHONY: all clean
+
+all: kexec_pe_parser_bpf.lskel.h
+
+clean:
+	$(call msg,CLEAN)
+	$(Q)rm -rf $(OUTPUT) kexec_pe_parser_bpf.lskel.h
+
+kexec_pe_parser_bpf.lskel.h: $(OUTPUT)/kexec_pe_parser_bpf.o | $(BPFTOOL)
+	$(call msg,GEN-SKEL,$@)
+	$(Q)$(BPFTOOL) gen skeleton -L $< > $@
+
+$(OUTPUT)/vmlinux.h: $(VMLINUX) $(BPFOBJ) | $(OUTPUT)
+	@$(BPFTOOL) btf dump file $(VMLINUX) format c > $(OUTPUT)/vmlinux.h
+
+
+$(OUTPUT)/kexec_pe_parser_bpf.o: kexec_pe_parser_bpf.c $(BPFOBJ) | $(OUTPUT)
+	$(call msg,BPF,$@)
+	$(Q)$(CLANG) -g -O2 -target bpf $(INCLUDES)			      \
+		 -c $(filter %.c,$^) -o $@ &&				      \
+	$(LLVM_STRIP) -g $@
+
+$(OUTPUT):
+	$(call msg,MKDIR,$@)
+	$(Q)mkdir -p $(OUTPUT)
+
+$(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(OUTPUT)
+	$(Q)$(MAKE) $(submake_extras) -C $(LIBBPF_SRC)			       \
+		    OUTPUT=$(abspath $(dir $@))/ $(abspath $@)
+
+$(DEFAULT_BPFTOOL):
+	$(Q)$(MAKE) $(submake_extras) -C ../../tools/bpf/bpftool			      \
+		    prefix= OUTPUT=$(abs_out)/ DESTDIR=$(abs_out) install

kernel/kexec_bpf/kexec_pe_parser_bpf.c

@@ -0,0 +1,67 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_core_read.h>
+#include <bpf/bpf_endian.h>
+#include <bpf/bpf_tracing.h>
+
+/*
+ * The ringbufs can have different capacity. But only four ringbuf are provided.
+ */
+#define RINGBUF1_SIZE	4
+#define RINGBUF2_SIZE	4
+#define RINGBUF3_SIZE	4
+#define RINGBUF4_SIZE	4
+
+#define KEXEC_RES_KERNEL_NAME "kexec:kernel"
+#define KEXEC_RES_INITRD_NAME "kexec:initrd"
+#define KEXEC_RES_CMDLINE_NAME "kexec:cmdline"
+
+/* ringbuf is safe since the user space has no write access to them */
+struct {
+	__uint(type, BPF_MAP_TYPE_RINGBUF);
+	__uint(max_entries, RINGBUF1_SIZE);
+} ringbuf_1 SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_RINGBUF);
+	__uint(max_entries, RINGBUF2_SIZE);
+} ringbuf_2 SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_RINGBUF);
+	__uint(max_entries, RINGBUF3_SIZE);
+} ringbuf_3 SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_RINGBUF);
+	__uint(max_entries, RINGBUF4_SIZE);
+} ringbuf_4 SEC(".maps");
+
+char LICENSE[] SEC("license") = "GPL";
+
+/*
+ * This function ensures that the sections .rodata, .data .bss and .rodata.str1.1
+ * are created for a bpf prog.
+ */
+__attribute__((used)) static int dummy(void)
+{
+	static const char res_kernel[16] __attribute__((used, section(".rodata"))) = KEXEC_RES_KERNEL_NAME;
+	static char local_name[16] __attribute__((used, section(".data"))) = KEXEC_RES_CMDLINE_NAME;
+	static char res_cmdline[16] __attribute__((used, section(".bss")));
+
+	__builtin_memcpy(local_name, KEXEC_RES_INITRD_NAME, 16);
+	return __builtin_memcmp(local_name, res_kernel, 4);
+}
+
+SEC("fentry.s/bpf_handle_pefile")
+__attribute__((used)) int BPF_PROG(parse_pe, struct kexec_context *context)
+{
+	return 0;
+}
+
+SEC("fentry.s/bpf_post_handle_pefile")
+__attribute__((used)) int BPF_PROG(post_parse_pe, struct kexec_context *context)
+{
+	return 0;
+}