On Wed, 10 Jun 2020 21:27:52 -0700 Vijay Balakrishna <vijayb@xxxxxxxxxxxxxxxxxxx> wrote:
> Make kernel GNU build-id available in VMCOREINFO. Having
> build-id in VMCOREINFO facilitates presenting appropriate kernel
> namelist image with debug information file to kernel crash dump
> analysis tools. Currently VMCOREINFO lacks uniquely identifiable
> key for crash analysis automation.
>
> Regarding if this patch is necessary or matching of linux_banner
> and OSRELEASE in VMCOREINFO employed by crash(8) meets the
> need -- IMO, build-id approach more foolproof, in most instances it
> is a cryptographic hash generated using internal code/ELF bits unlike
> kernel version string upon which linux_banner is based that is
> external to the code. I feel each is intended for a different purpose.
> Also OSRELEASE is not suitable when two different kernel builds
> from same version with different features enabled.
>
> Currently for most linux (and non-linux) systems build-id can be
> extracted using standard methods for file types such as user mode crash
> dumps, shared libraries, loadable kernel modules etc., This is an
> exception for linux kernel dump. Having build-id in VMCOREINFO brings
> some uniformity for automation tools.
>
> ...
>
> --- a/kernel/crash_core.c
> +++ b/kernel/crash_core.c
> @@ -11,6 +11,8 @@
> #include <asm/page.h>
> #include <asm/sections.h>
>
> +#include <crypto/sha.h>
> +
> /* vmcoreinfo stuff */
> unsigned char *vmcoreinfo_data;
> size_t vmcoreinfo_size;
> @@ -376,6 +378,53 @@ phys_addr_t __weak paddr_vmcoreinfo_note(void)
> }
> EXPORT_SYMBOL(paddr_vmcoreinfo_note);
>
> +#define NOTES_SIZE (&__stop_notes - &__start_notes)
> +#define BUILD_ID_MAX SHA1_DIGEST_SIZE
> +#define NT_GNU_BUILD_ID 3
> +
> +struct elf_note_section {
> + struct elf_note n_hdr;
> + u8 n_data[];
> +};
> +
> +/*
> + * Add build ID from .notes section as generated by the GNU ld(1)
> + * or LLVM lld(1) --build-id option.
> + */
> +static void add_build_id_vmcoreinfo(void)
> +{
> + char build_id[BUILD_ID_MAX * 2 + 1];
> + int n_remain = NOTES_SIZE;
> +
> + while (n_remain >= sizeof(struct elf_note)) {
> + const struct elf_note_section *note_sec =
> + &__start_notes + NOTES_SIZE - n_remain;
> + const u32 n_namesz = note_sec->n_hdr.n_namesz;
> +
> + if (note_sec->n_hdr.n_type == NT_GNU_BUILD_ID &&
> + n_namesz != 0 &&
> + !strcmp((char *)¬e_sec->n_data[0], "GNU")) {
Is it guaranteed that n_data[] is null-terminated?
> + if (note_sec->n_hdr.n_descsz <= BUILD_ID_MAX) {
> + const u32 n_descsz = note_sec->n_hdr.n_descsz;
> + const u8 *s = ¬e_sec->n_data[n_namesz];
> +
> + s = PTR_ALIGN(s, 4);
> + bin2hex(build_id, s, n_descsz);
> + build_id[2 * n_descsz] = '\0';
> + VMCOREINFO_BUILD_ID(build_id);
> + return;
> + }
> + pr_warn("Build ID is too large to include in vmcoreinfo: %u > %u\n",
> + note_sec->n_hdr.n_descsz,
> + BUILD_ID_MAX);
> + return;
> + }
> + n_remain -= sizeof(struct elf_note) +
> + ALIGN(note_sec->n_hdr.n_namesz, 4) +
> + ALIGN(note_sec->n_hdr.n_descsz, 4);
> + }
> +}
> +
> static int __init crash_save_vmcoreinfo_init(void)
> {
> vmcoreinfo_data = (unsigned char *)get_zeroed_page(GFP_KERNEL);
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