linux-kernel - Re: [PATCH] vmlinux.lds.h: Handle decrypted data section with !SMP

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Date:   Thu, 6 May 2021 11:15:30 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Arnd Bergmann <arnd@...db.de>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        kernel test robot <lkp@...el.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH] vmlinux.lds.h: Handle decrypted data section with !SMP

On Wed, May 5, 2021 at 5:28 PM Nathan Chancellor <nathan@...nel.org> wrote:
>
> With x86_64_defconfig and the following configs, there is an orphan
> section warning:
>
> CONFIG_SMP=n
> CONFIG_AMD_MEM_ENCRYPT=y
> CONFIG_HYPERVISOR_GUEST=y
> CONFIG_KVM=y
> CONFIG_PARAVIRT=y
>
> ld: warning: orphan section `.data..decrypted' from `arch/x86/kernel/cpu/vmware.o' being placed in section `.data..decrypted'
> ld: warning: orphan section `.data..decrypted' from `arch/x86/kernel/kvm.o' being placed in section `.data..decrypted'
>
> These sections are created with DEFINE_PER_CPU_DECRYPTED, which
> ultimately turns into __PCPU_ATTRS, which in turn has a section
> attribute with a value of PER_CPU_BASE_SECTION + the section name. When
> CONFIG_SMP is not set, the base section is .data and that is not
> currently handled in any linker script.
>
> Add .data..decrypted to PERCPU_DECRYPTED_SECTION, which is included in
> PERCPU_INPUT -> PERCPU_SECTION, which is include in the x86 linker
> script when either CONFIG_X86_64 or CONFIG_SMP is unset, taking care of
> the warning.
>
> Fixes: ac26963a1175 ("percpu: Introduce DEFINE_PER_CPU_DECRYPTED")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1360
> Reported-by: kernel test robot <lkp@...el.com>
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>

Thanks for the patch; LGTM.

Reviewed-by:Nick Desaulniers <ndesaulniers@...gle.com>
Tested-by: Nick Desaulniers <ndesaulniers@...gle.com> # build

> ---
>
> I took the simple fix route with this patch since I highly doubt someone
> is actually running a CONFIG_AMD_MEM_ENCRYPT=y + CONFIG_SMP=n kernel. If
> this section should actually be in .data, I can respin.
>
>  include/asm-generic/vmlinux.lds.h | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index 40a9c101565e..17325416e2de 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -960,6 +960,7 @@
>  #ifdef CONFIG_AMD_MEM_ENCRYPT
>  #define PERCPU_DECRYPTED_SECTION                                       \
>         . = ALIGN(PAGE_SIZE);                                           \
> +       *(.data..decrypted)                                             \
>         *(.data..percpu..decrypted)                                     \
>         . = ALIGN(PAGE_SIZE);
>  #else
>
> base-commit: 8404c9fbc84b741f66cff7d4934a25dd2c344452
> --
> 2.31.1.442.g7e39198978
>


-- 
Thanks,
~Nick Desaulniers