Hi Pingfan,
On Thu, 29 May 2025 12:17:43 +0800
Pingfan Liu <pi...@redhat.com> wrote:
> 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 <pi...@redhat.com>
> Cc: Alexei Starovoitov <a...@kernel.org>
> Cc: Baoquan He <b...@redhat.com>
> Cc: Dave Young <dyo...@redhat.com>
> Cc: Andrew Morton <a...@linux-foundation.org>
> Cc: Philipp Rudo <pr...@redhat.com>
> Cc: b...@vger.kernel.org
> To: kexec@lists.infradead.org
> ---
> kernel/Makefile | 1 +
> kernel/kexec_bpf/Makefile | 8 +
> kernel/kexec_bpf/kexec_pe_parser_bpf.lskel.h | 292 +------------------
> kernel/kexec_pe_image.c | 70 +++++
> 4 files changed, 83 insertions(+), 288 deletions(-)
>
[...]
> diff --git a/kernel/kexec_pe_image.c b/kernel/kexec_pe_image.c
> index e49d6db3c329d..f47c1e46dba97 100644
> --- a/kernel/kexec_pe_image.c
> +++ b/kernel/kexec_pe_image.c
> @@ -13,6 +13,7 @@
> #include <linux/kernel.h>
> #include <linux/vmalloc.h>
> #include <linux/kexec.h>
> +#include <linux/elf.h>
> #include <linux/pe.h>
> #include <linux/string.h>
> #include <linux/bpf.h>
> @@ -21,6 +22,7 @@
> #include <asm/image.h>
> #include <asm/memory.h>
>
> +#include "kexec_bpf/kexec_pe_parser_bpf.lskel.h"
>
> static LIST_HEAD(phase_head);
>
> @@ -163,14 +165,82 @@ static bool pe_has_bpf_section(char *file_buf, unsigned
> long pe_sz)
> return true;
> }
>
> +static struct kexec_pe_parser_bpf *pe_parser;
> +
> +static void *get_symbol_from_elf(const char *elf_data, size_t elf_size,
> + const char *symbol_name, unsigned int *symbol_size)
> +{
> + Elf_Ehdr *ehdr = (Elf_Ehdr *)elf_data;
> + Elf_Shdr *shdr, *symtab_shdr, *strtab_shdr, *dst_shdr;
> + Elf64_Sym *sym, *symtab = NULL;
> + char *strtab = NULL;
> + void *symbol_data = NULL;
> + int i;
> +
> + symtab_shdr = strtab_shdr = NULL;
> + if (memcmp(ehdr->e_ident, ELFMAG, SELFMAG) != 0) {
> + pr_err("Not a valid ELF file\n");
> + goto out;
> + }
> +
> + shdr = (struct elf_shdr *)(elf_data + ehdr->e_shoff);
> + for (i = 0; i < ehdr->e_shnum; i++) {
> + if (shdr[i].sh_type == SHT_SYMTAB)
> + symtab_shdr = &shdr[i];
> + else if (shdr[i].sh_type == SHT_STRTAB && i != ehdr->e_shstrndx)
> + strtab_shdr = &shdr[i];
> + }
> +
> + if (!symtab_shdr || !strtab_shdr) {
> + pr_err("Symbol table or string table not found\n");
> + goto out;
> + }
> + symtab = (Elf64_Sym *)(elf_data + symtab_shdr->sh_offset);
> + strtab = (char *)(elf_data + strtab_shdr->sh_offset);
> + for (i = 0; i < symtab_shdr->sh_size / sizeof(Elf64_Sym); i++) {
> + sym = &symtab[i];
> + if (strcmp(&strtab[sym->st_name], symbol_name) == 0) {
> + if (sym->st_shndx >= SHN_LORESERVE)
> + return NULL; // No section data for these
> + dst_shdr = &shdr[sym->st_shndx];
> + symbol_data = (void *)(elf_data + dst_shdr->sh_offset +
> sym->st_value);
> + *symbol_size = symtab[i].st_size;
> + break;
> + }
> + }
> +
> +out:
> + return symbol_data;
> +}
In kernel/kexec_file.c there is kexec_purgatory_find_symbol which is
basically identical to this function. With a little bit of refractoring
it should work for both cases. I prefer using
kexec_purgatory_find_symbol as your implementation cannot handle elf
files with multiple symtab and strtab sections.
Thanks
Philipp
> +
> /* Load a ELF */
> static int arm_bpf_prog(char *bpf_elf, unsigned long sz)
> {
> + opts_data = get_symbol_from_elf(bpf_elf, sz, "opts_data",
> &opts_data_sz);
> + opts_insn = get_symbol_from_elf(bpf_elf, sz, "opts_insn",
> &opts_insn_sz);
> + if (!opts_data || !opts_insn)
> + return -1;
> + /*
> + * When light skeleton generates opts_data[] and opts_insn[], it
> appends a
> + * NULL terminator at the end of string
> + */
> + opts_data_sz = opts_data_sz - 1;
> + opts_insn_sz = opts_insn_sz - 1;
> +
> + pe_parser = kexec_pe_parser_bpf__open_and_load();
> + if (!pe_parser)
> + return -1;
> + kexec_pe_parser_bpf__attach(pe_parser);
> +
> return 0;
> }
>
> static void disarm_bpf_prog(void)
> {
> + kexec_pe_parser_bpf__destroy(pe_parser);
> + pe_parser = NULL;
> + opts_data = NULL;
> + opts_insn = NULL;
> }
>
> struct kexec_context {
