linux-kernel - Re: [PATCH 2/2] arm64: acpi: Prepare for longer MADTs

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Message-ID: <20181015092919.GA1778@e107155-lin>
Date:   Mon, 15 Oct 2018 10:29:19 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Jeremy Linton <jeremy.linton@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, catalin.marinas@....com,
        will.deacon@....com, ard.biesheuvel@...aro.org,
        james.morse@....com, rafael.j.wysocki@...el.com,
        takahiro.akashi@...aro.org, lorenzo.pieralisi@....com,
        ahs3@...hat.com, linux-acpi@...r.kernel.org,
        linux-kernel@...r.kernel.org, Sudeep Holla <sudeep.holla@....com>
Subject: Re: [PATCH 2/2] arm64: acpi: Prepare for longer MADTs

On Fri, Oct 12, 2018 at 02:29:37PM -0500, Jeremy Linton wrote:
> The BAD_MADT_GICC_ENTRY check is a little too strict because
> it rejects MADT entries that don't match the currently known
> lengths. We should remove this restriction to avoid problems
> if the table length changes. Future code which might depend on
> additional fields should be written to validate those fields
> before using them, rather than trying to globally check
> known MADT version lengths.
>
> Signed-off-by: Jeremy Linton <jeremy.linton@....com>
> ---
>  arch/arm64/include/asm/acpi.h | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm64/include/asm/acpi.h b/arch/arm64/include/asm/acpi.h
> index 709208dfdc8b..4d0946bd485a 100644
> --- a/arch/arm64/include/asm/acpi.h
> +++ b/arch/arm64/include/asm/acpi.h
> @@ -22,12 +22,12 @@
>  #include <asm/tlbflush.h>
>
>  /* Macros for consistency checks of the GICC subtable of MADT */
> -#define ACPI_MADT_GICC_LENGTH	\
> -	(acpi_gbl_FADT.header.revision < 6 ? 76 : 80)
> +#define ACPI_MADT_GICC_MIN_LENGTH   ACPI_OFFSET(  \
> +	struct acpi_madt_generic_interrupt, efficiency_class)
>

This makes it 76 always which is fine, just that the first user of
efficiency_class should check for the length before accessing it.
No user of efficiency_class yet, so I am fine with this change.

>  #define BAD_MADT_GICC_ENTRY(entry, end)					\
> -	(!(entry) || (entry)->header.length != ACPI_MADT_GICC_LENGTH ||	\
> -	(unsigned long)(entry) + ACPI_MADT_GICC_LENGTH > (end))
> +	(!(entry) || (entry)->header.length < ACPI_MADT_GICC_MIN_LENGTH || \
> +	(unsigned long)(entry) + (entry)->header.length > (end))
>

Acked-by: Sudeep Holla <sudeep.holla@....com>

--
Regards,
Sudeep