From: Kees Cook <keescook@chromium.org>
To: Will Deacon <will@kernel.org>
Cc: Fangrui Song <maskray@google.com>,
Ard Biesheuvel <ard.biesheuvel@linaro.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
clang-built-linux <clang-built-linux@googlegroups.com>,
Peter Smith <peter.smith@linaro.org>,
Nathan Chancellor <natechancellor@gmail.com>,
linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] arm64/efi: Move variable assignments after SECTIONS
Date: Wed, 14 Aug 2019 09:35:18 -0700 [thread overview]
Message-ID: <201908140934.C3F1F7151E@keescook> (raw)
In-Reply-To: <20190814161904.55jgaxnhd4ujyh2h@willie-the-truck>
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
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linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
WARNING: multiple messages have this Message-ID (diff)
From: Kees Cook <keescook@chromium.org>
To: Will Deacon <will@kernel.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>,
Nathan Chancellor <natechancellor@gmail.com>,
Catalin Marinas <catalin.marinas@arm.com>,
linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
clang-built-linux <clang-built-linux@googlegroups.com>,
Fangrui Song <maskray@google.com>,
Peter Smith <peter.smith@linaro.org>
Subject: Re: [PATCH] arm64/efi: Move variable assignments after SECTIONS
Date: Wed, 14 Aug 2019 09:35:18 -0700 [thread overview]
Message-ID: <201908140934.C3F1F7151E@keescook> (raw)
In-Reply-To: <20190814161904.55jgaxnhd4ujyh2h@willie-the-truck>
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
next prev parent reply other threads:[~2019-08-14 16:35 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-13 23:04 [PATCH] arm64/efi: Move variable assignments after SECTIONS Kees Cook
2019-08-13 23:04 ` Kees Cook
2019-08-14 16:14 ` Ard Biesheuvel
2019-08-14 16:14 ` Ard Biesheuvel
2019-08-14 16:19 ` Will Deacon
2019-08-14 16:19 ` Will Deacon
2019-08-14 16:35 ` Kees Cook [this message]
2019-08-14 16:35 ` Kees Cook
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