On Tue, Apr 28, 2020 at 06:21:05AM -0700, H.J. Lu wrote:
> With the command-line option, -mx86-used-note=yes, the x86 assembler
> in binutils 2.32 and above generates a program property note in a note
> section, .note.gnu.property, to encode used x86 ISAs and features. But
> kernel linker script only contains a single NOTE segment:
>
> PHDRS {
> text PT_LOAD FLAGS(5);
> data PT_LOAD FLAGS(6);
> percpu PT_LOAD FLAGS(6);
> init PT_LOAD FLAGS(7);
> note PT_NOTE FLAGS(0);
> }
> SECTIONS
> {
> ...
> .notes : AT(ADDR(.notes) - 0xffffffff80000000) { __start_notes = .; KEEP(*(.not
> e.*)) __stop_notes = .; } :text :note
> ...
> }
>
> The NOTE segment generated by kernel linker script is aligned to 4 bytes.
> But .note.gnu.property section must be aligned to 8 bytes on x86-64 and
> we get
>
> [hjl@gnu-skx-1 linux]$ readelf -n vmlinux
>
> Displaying notes found in: .notes
> Owner Data size Description
> Xen 0x00000006 Unknown note type: (0x00000006)
> description data: 6c 69 6e 75 78 00
> Xen 0x00000004 Unknown note type: (0x00000007)
> description data: 32 2e 36 00
> xen-3.0 0x00000005 Unknown note type: (0x006e6558)
> description data: 08 00 00 00 03
> readelf: Warning: note with invalid namesz and/or descsz found at offset 0x50
> readelf: Warning: type: 0xffffffff, namesize: 0x006e6558, descsize:
> 0x80000000, alignment: 8
> [hjl@gnu-skx-1 linux]$
>
> Since note.gnu.property section in kernel image is never used, this patch
> discards .note.gnu.property sections in kernel linker script by adding
>
> /DISCARD/ : {
> *(.note.gnu.property)
> }
>
> before kernel NOTE segment in generic NOTES.
>
> Signed-off-by: H.J. Lu <hjl.tools@xxxxxxxxx>
> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
> ---
> include/asm-generic/vmlinux.lds.h | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index 71e387a5fe90..95cd678428f4 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -833,7 +833,14 @@
> #define TRACEDATA
> #endif
>
> +/*
> + * Discard .note.gnu.property sections which are unused and have
> + * different alignment requirement from kernel note sections.
> + */
> #define NOTES \
> + /DISCARD/ : { \
> + *(.note.gnu.property) \
> + } \
> .notes : AT(ADDR(.notes) - LOAD_OFFSET) { \
> __start_notes = .; \
> KEEP(*(.note.*)) \
> --
> 2.25.4
>
Hi, H.J.,
I recently ran into this same .notes corruption when building kernels on
Arch Linux.
What ended up happening to this patch? It doesn't appear to have been
merged, and I couldn't find any further discussion about it. I'm happy
to resend it for you if you need a hand.
Thanks,
Omar
