Re: [PATCH v2][RFC] kdump: append kernel build-id string to VMCOREINFO

From: Baoquan He
Date: Wed Jun 17 2020 - 08:53:28 EST


On 06/10/20 at 09:27pm, Vijay Balakrishna 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.
>
> Signed-off-by: Vijay Balakrishna <vijayb@xxxxxxxxxxxxxxxxxxx>

Looks good to me, thanks.

Acked-by: Baoquan He <bhe@xxxxxxxxxx>

> ---
> Changes since v2:
> -----------------
> - v1 was sent out as a single patch which can be seen here:
> http://lists.infradead.org/pipermail/kexec/2020-June/025202.html
> - moved justification to commit commit log
> - renamed 'g_build_id' to 'note_sec'
> - fixed format specifier in pr_warn() from '%lu' to '%u' (failed to
> catch warning in v1)
>
> include/linux/crash_core.h | 6 +++++
> kernel/crash_core.c | 50 ++++++++++++++++++++++++++++++++++++++
> 2 files changed, 56 insertions(+)
>
> diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
> index 525510a9f965..6594dbc34a37 100644
> --- a/include/linux/crash_core.h
> +++ b/include/linux/crash_core.h
> @@ -38,6 +38,8 @@ phys_addr_t paddr_vmcoreinfo_note(void);
>
> #define VMCOREINFO_OSRELEASE(value) \
> vmcoreinfo_append_str("OSRELEASE=%s\n", value)
> +#define VMCOREINFO_BUILD_ID(value) \
> + vmcoreinfo_append_str("BUILD-ID=%s\n", value)
> #define VMCOREINFO_PAGESIZE(value) \
> vmcoreinfo_append_str("PAGESIZE=%ld\n", value)
> #define VMCOREINFO_SYMBOL(name) \
> @@ -64,6 +66,10 @@ extern unsigned char *vmcoreinfo_data;
> extern size_t vmcoreinfo_size;
> extern u32 *vmcoreinfo_note;
>
> +/* raw contents of kernel .notes section */
> +extern const void __start_notes __weak;
> +extern const void __stop_notes __weak;
> +
> Elf_Word *append_elf_note(Elf_Word *buf, char *name, unsigned int type,
> void *data, size_t data_len);
> void final_note(Elf_Word *buf);
> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> index 9f1557b98468..64ac359cd17e 100644
> --- 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 *)&note_sec->n_data[0], "GNU")) {
> + if (note_sec->n_hdr.n_descsz <= BUILD_ID_MAX) {
> + const u32 n_descsz = note_sec->n_hdr.n_descsz;
> + const u8 *s = &note_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);
> @@ -394,6 +443,7 @@ static int __init crash_save_vmcoreinfo_init(void)
> }
>
> VMCOREINFO_OSRELEASE(init_uts_ns.name.release);
> + add_build_id_vmcoreinfo();
> VMCOREINFO_PAGESIZE(PAGE_SIZE);
>
> VMCOREINFO_SYMBOL(init_uts_ns);
> --
> 2.26.2
>
>
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