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

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Date:   Fri, 4 Jun 2021 17:20:36 +0100
From:   James Morse <james.morse@....com>
To:     Marc Zyngier <maz@...nel.org>, kexec@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Mark Rutland <mark.rutland@....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>, kernel-team@...roid.com,
        stable@...r.kernel.org
Subject: Re: [PATCH v2 1/5] arm64: kexec_file: Forbid non-crash kernels

On 31/05/2021 10:57, Marc Zyngier 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.

I'd like to know how the ACPI tables bit happens.

ACPI tables should be in EFI_ACPI_RECLAIM_MEMORY or EFI_ACPI_MEMORY_NVS (which isn't
treated as usable).

EFI's reserve_regions() does this:
|	if (!is_usable_memory(md))
|		memblock_mark_nomap(paddr, size);
|
|	/* keep ACPI reclaim memory intact for kexec etc. */
|	if (md->type == EFI_ACPI_RECLAIM_MEMORY)
|		memblock_reserve(paddr, size);

which is called via efi_init(), and all those regions end up listed as reserved in
/proc/iomem. (this is why arm64 doesn't call acpi_reserve_initial_tables())

If your firmware puts ACPI tables are in EFI_CONVENTIONAL_MEMORY, you have bigger problems
as the kernel could get relocated over the top of them during boot, and even if it
doesn't, nothing stops that  memory being allocated for user-space.

Even acpi_table_upgrade() calls memblock_reserve() and happens early enough not to be a
problem.

Please share ... enjoyment, optional.

(boot with efi=debug and post the EFI memory map and the 'ACPI: FOO 0xphysicaladdress'
stuff at the top of the boot log)

Thanks,

James

> 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.