lkml.org 
[lkml]   [2019]   [Aug]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] arm64/efi: Move variable assignments after SECTIONS
On Wed, Aug 14, 2019 at 05:19:04PM +0100, Will Deacon wrote:
> On Wed, Aug 14, 2019 at 07:14:42PM +0300, Ard Biesheuvel wrote:
> > On Wed, 14 Aug 2019 at 02:04, Kees Cook <keescook@chromium.org> wrote:
> > >
> > > It seems that LLVM's linker does not correctly handle variable assignments
> > > involving section positions that are updated during the SECTIONS
> > > parsing. Commit aa69fb62bea1 ("arm64/efi: Mark __efistub_stext_offset as
> > > an absolute symbol explicitly") ran into this too, but found a different
> > > workaround.
> > >
> > > However, this was not enough, as other variables were also miscalculated
> > > which manifested as boot failures under UEFI where __efistub__end was
> > > not taking the correct _end value (they should be the same):
> > >
> > > $ ld.lld -EL -maarch64elf --no-undefined -X -shared \
> > > -Bsymbolic -z notext -z norelro --no-apply-dynamic-relocs \
> > > -o vmlinux.lld -T poc.lds --whole-archive vmlinux.o && \
> > > readelf -Ws vmlinux.lld | egrep '\b(__efistub_|)_end\b'
> > > 368272: ffff000002218000 0 NOTYPE LOCAL HIDDEN 38 __efistub__end
> > > 368322: ffff000012318000 0 NOTYPE GLOBAL DEFAULT 38 _end
> > >
> > > $ aarch64-linux-gnu-ld.bfd -EL -maarch64elf --no-undefined -X -shared \
> > > -Bsymbolic -z notext -z norelro --no-apply-dynamic-relocs \
> > > -o vmlinux.bfd -T poc.lds --whole-archive vmlinux.o && \
> > > readelf -Ws vmlinux.bfd | egrep '\b(__efistub_|)_end\b'
> > > 338124: ffff000012318000 0 NOTYPE LOCAL DEFAULT ABS __efistub__end
> > > 383812: ffff000012318000 0 NOTYPE GLOBAL DEFAULT 15325 _end
> > >
> > > To work around this, all of the __efistub_-prefixed variable assignments
> > > need to be moved after the linker script's SECTIONS entry. As it turns
> > > out, this also solves the problem fixed in commit aa69fb62bea1, so those
> > > changes are reverted here.
> > >
> > > Link: https://github.com/ClangBuiltLinux/linux/issues/634
> > > Link: https://bugs.llvm.org/show_bug.cgi?id=42990
> > > Signed-off-by: Kees Cook <keescook@chromium.org>
> >
> > Although it is slightly disappointing that we need to work around this
> > kind of bugs when adding support for a new toolchain, I don't see
> > anything wrong with this patch, so
> >
> > Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>
> Yup, it's gross, but I'll queue it with your ack.

Thanks, and agreed. :)

--
Kees Cook

\
 
 \ /
  Last update: 2019-08-14 18:36    [W:0.068 / U:0.576 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site