kexec: Integrate bpf light skeleton to load zboot image

All kexec PE bpf prog should align with the interface exposed by the
light skeleton
    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")

With the above presumption, the integration consists of two parts:
  -1. Call API exposed by light skeleton from kexec
  -2. The opts_insn[] and opts_data[] are bpf-prog dependent and
      can be extracted and passed in from the user space. In the
      kexec_file_load design, a PE file has a .bpf section, which data
      content is a ELF, and the ELF contains opts_insn[] opts_data[].
      As a bonus, BPF bytecode can be placed under the protection of the
      entire PE signature.
      (Note, since opts_insn[] contains the information of the ringbuf
       size, the bpf-prog writer can change its proper size according to
       the kernel image size without modifying the kernel code)

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/Makefile

@@ -142,6 +142,7 @@ obj-$(CONFIG_SYSCTL_KUNIT_TEST) += sysctl-test.o
 
 CFLAGS_kstack_erase.o += $(DISABLE_KSTACK_ERASE)
 CFLAGS_kstack_erase.o += $(call cc-option,-mgeneral-regs-only)
+CFLAGS_kexec_pe_image.o += -I$(srctree)/tools/lib
 obj-$(CONFIG_KSTACK_ERASE) += kstack_erase.o
 KASAN_SANITIZE_kstack_erase.o := n
 KCSAN_SANITIZE_kstack_erase.o := n

kernel/kexec_bpf/Makefile

@@ -39,6 +39,14 @@ clean:
 kexec_pe_parser_bpf.lskel.h: $(OUTPUT)/kexec_pe_parser_bpf.o | $(BPFTOOL)
 	$(call msg,GEN-SKEL,$@)
 	$(Q)$(BPFTOOL) gen skeleton -L $< > $@
+	@# The following sed commands make opts_data[] and opts_insn[] visible in a file instead of only in a function.
+	@# And it removes the bytecode
+	$(Q) sed -i '/static const char opts_data\[\].*=/,/";$$/d' $@
+	$(Q) sed -i '/static const char opts_insn\[\].*=/,/";$$/d' $@
+	$(Q) sed -i \
+		-e 's/opts\.data_sz = sizeof(opts_data) - 1;/opts.data_sz = opts_data_sz;/' \
+		-e 's/opts\.insns_sz = sizeof(opts_insn) - 1;/opts.insns_sz = opts_insn_sz;/' $@
+	$(Q) sed -i '7i static char *opts_data, *opts_insn;\nstatic unsigned int opts_data_sz, opts_insn_sz;' $@
 
 $(OUTPUT)/vmlinux.h: $(VMLINUX) $(BPFOBJ) | $(OUTPUT)
 	@$(BPFTOOL) btf dump file $(VMLINUX) format c > $(OUTPUT)/vmlinux.h