On 2020-06-10 21:27:52, 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> I think this is a nice improvement over today's linux_banner approach for correlating vmlinux to a kernel dump. The elf notes parsing in this patch lines up with what is described in in the "Notes (Nhdr)" section of the elf(5) man page. BUILD_ID_MAX is sufficient to hold a sha1 build-id, which is the default build-id type today in GNU ld(2). It is also sufficient to hold the "fast" build-id, which is the default build-id type today in LLVM lld(2). Therefore, Reviewed-by: Tyler Hicks <tyhicks@xxxxxxxxxxxxxxxxxxx> Thanks! Tyler > --- > 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 *)¬e_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 = ¬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); > @@ -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 _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
