Hi Kees,
On Fri, Aug 21, 2020 at 9:56 PM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> In preparation for warning on orphan sections, discard
> unwanted non-zero-sized generated sections, and enforce other
> expected-to-be-zero-sized sections (since discarding them might hide
> problems with them suddenly gaining unexpected entries).
>
> Suggested-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
This is now commit be2881824ae9eb92 ("arm64/build: Assert for unwanted
sections") in v5.10-rc1, and is causing the following error with
renesas_defconfig[1]:
aarch64-linux-gnu-ld: warning: orphan section `.eh_frame' from
`kernel/bpf/core.o' being placed in section `.eh_frame'
aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected!
aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected!
I cannot reproduce this with the standard arm64 defconfig.
I bisected the error to the aforementioned commit, but understand this
is not the real reason. If I revert this commit, I still get:
aarch64-linux-gnu-ld: warning: orphan section `.got.plt' from
`arch/arm64/kernel/head.o' being placed in section `.got.plt'
aarch64-linux-gnu-ld: warning: orphan section `.plt' from
`arch/arm64/kernel/head.o' being placed in section `.plt'
aarch64-linux-gnu-ld: warning: orphan section `.data.rel.ro' from
`arch/arm64/kernel/head.o' being placed in section `.data.rel.ro'
aarch64-linux-gnu-ld: warning: orphan section `.eh_frame' from
`kernel/bpf/core.o' being placed in section `.eh_frame'
I.e. including the ".eh_frame" warning. I have tried bisecting that
warning (i.e. with be2881824ae9eb92 reverted), but that leads me to
commit b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section
placement"), which is another red herring.
Note that even on plain be2881824ae9eb92, I get:
aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected!
aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected!
The parent commit obviously doesn't show that (but probably still has
the problem).
Do you have a clue!
Thanks!
> --- a/arch/arm64/kernel/vmlinux.lds.S
> +++ b/arch/arm64/kernel/vmlinux.lds.S
> @@ -121,6 +121,14 @@ SECTIONS
> *(.got) /* Global offset table */
> }
>
> + /*
> + * Make sure that the .got.plt is either completely empty or it
> + * contains only the lazy dispatch entries.
> + */
> + .got.plt : { *(.got.plt) }
> + ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0x18,
> + "Unexpected GOT/PLT entries detected!")
> +
> . = ALIGN(SEGMENT_ALIGN);
> _etext = .; /* End of text section */
>
> @@ -243,6 +251,18 @@ SECTIONS
> ELF_DETAILS
>
> HEAD_SYMBOLS
> +
> + /*
> + * Sections that should stay zero sized, which is safer to
> + * explicitly check instead of blindly discarding.
> + */
> + .plt : {
> + *(.plt) *(.plt.*) *(.iplt) *(.igot)
> + }
> + ASSERT(SIZEOF(.plt) == 0, "Unexpected run-time procedure linkages detected!")
> +
> + .data.rel.ro : { *(.data.rel.ro) }
> + ASSERT(SIZEOF(.data.rel.ro) == 0, "Unexpected RELRO detected!")
> }
>
> #include "image-vars.h"
[1] https://git.kernel.org/pub/scm/linux/kernel/git/geert/renesas-devel.git/log/?h=topic/renesas-defconfig
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
