linux-kernel - Re: [PATCH v2 1/5] arm64: kexec_file: Forbid non-crash kernels

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Date:   Mon, 31 May 2021 21:37:49 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Marc Zyngier <maz@...nel.org>
Cc:     kexec@...ts.infradead.org,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        James Morse <james.morse@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Hanjun Guo <guohanjun@...wei.com>,
        Sudeep Holla <sudeep.holla@....com>,
        Eric Biederman <ebiederm@...ssion.com>,
        Bhupesh SHARMA <bhupesh.sharma@...aro.org>,
        AKASHI Takahiro <takahiro.akashi@...aro.org>,
        Dave Young <dyoung@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Moritz Fischer <mdf@...nel.org>,
        Android Kernel Team <kernel-team@...roid.com>,
        "# 3.4.x" <stable@...r.kernel.org>
Subject: Re: [PATCH v2 1/5] arm64: kexec_file: Forbid non-crash kernels

On Mon, 31 May 2021 at 11:57, Marc Zyngier <maz@...nel.org> wrote:
>
> It has been reported that kexec_file doesn't really work on arm64.
> It completely ignores any of the existing reservations, which results
> in the secondary kernel being loaded where the GICv3 LPI tables live,
> or even corrupting the ACPI tables.
>
> Since only crash kernels are imune to this as they use a reserved
> memory region, disable the non-crash kernel use case. Further
> patches will try and restore the functionality.
>
> Reported-by: Moritz Fischer <mdf@...nel.org>
> Signed-off-by: Marc Zyngier <maz@...nel.org>
> Cc: stable@...r.kernel.org # 5.10

Acked-by: Ard Biesheuvel <ardb@...nel.org>

... but do we really only need this in 5.10 and not earlier?

> ---
>  arch/arm64/kernel/kexec_image.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
>
> diff --git a/arch/arm64/kernel/kexec_image.c b/arch/arm64/kernel/kexec_image.c
> index 9ec34690e255..acf9cd251307 100644
> --- a/arch/arm64/kernel/kexec_image.c
> +++ b/arch/arm64/kernel/kexec_image.c
> @@ -145,3 +145,23 @@ const struct kexec_file_ops kexec_image_ops = {
>         .verify_sig = image_verify_sig,
>  #endif
>  };
> +
> +/**
> + * arch_kexec_locate_mem_hole - Find free memory to place the segments.
> + * @kbuf:                       Parameters for the memory search.
> + *
> + * On success, kbuf->mem will have the start address of the memory region found.
> + *
> + * Return: 0 on success, negative errno on error.
> + */
> +int arch_kexec_locate_mem_hole(struct kexec_buf *kbuf)
> +{
> +       /*
> +        * For the time being, kexec_file_load isn't reliable except
> +        * for crash kernel. Say sorry to the user.
> +        */
> +       if (kbuf->image->type != KEXEC_TYPE_CRASH)
> +               return -EADDRNOTAVAIL;
> +
> +       return kexec_locate_mem_hole(kbuf);
> +}
> --
> 2.30.2
>