Re: [PATCH 3/4] acpi: fix OEM ID/OEM Table ID padding

[Ani Sinha]

On Wed, 12 Jan 2022, Igor Mammedov wrote:

> Commit [2] broke original '\0' padding of OEM ID and OEM Table ID
> fields in headers of ACPI tables. While it doesn't have impact on
> default values since QEMU uses 6 and 8 characters long values
> respectively, it broke usecase where IDs are provided on QEMU CLI.
> It shouldn't affect guest (but may cause licensing verification
> issues in guest OS).
> One of the broken usecases is user supplied SLIC table with IDs
> shorter than max possible length, where [2] mangles IDs with extra
> spaces in RSDT and FADT tables whereas guest OS expects those to
> mirror the respective values of the used SLIC table.
>
> Fix it by replacing whitespace padding with '\0' padding in
> accordance with [1] and expectations of guest OS
>
> 1) ACPI spec, v2.0b
>        17.2 AML Grammar Definition
>        ...
>        //OEM ID of up to 6 characters. If the OEM ID is
>        //shorter than 6 characters, it can be terminated
>        //with a NULL character.
>
> 2)
> Fixes: 602b458201 ("acpi: Permit OEM ID and OEM table ID fields to be 
> changed")
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/707
> Reported-by: Dmitry V. Orekhov <dima.orekhov@gmail.com>
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> Cc: qemu-stable@nongnu.org

Reviewed-by: Ani Sinha <ani@anisinha.ca>

> ---
>  hw/acpi/aml-build.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/hw/acpi/aml-build.c b/hw/acpi/aml-build.c
> index b3b3310df3..65148d5b9d 100644
> --- a/hw/acpi/aml-build.c
> +++ b/hw/acpi/aml-build.c
> @@ -1724,9 +1724,9 @@ void acpi_table_begin(AcpiTable *desc, GArray *array)
>      build_append_int_noprefix(array, 0, 4); /* Length */
>      build_append_int_noprefix(array, desc->rev, 1); /* Revision */
>      build_append_int_noprefix(array, 0, 1); /* Checksum */
> -    build_append_padded_str(array, desc->oem_id, 6, ' '); /* OEMID */
> +    build_append_padded_str(array, desc->oem_id, 6, '\0'); /* OEMID */
>      /* OEM Table ID */
> -    build_append_padded_str(array, desc->oem_table_id, 8, ' ');
> +    build_append_padded_str(array, desc->oem_table_id, 8, '\0');
>      build_append_int_noprefix(array, 1, 4); /* OEM Revision */
>      g_array_append_vals(array, ACPI_BUILD_APPNAME8, 4); /* Creator ID */
>      build_append_int_noprefix(array, 1, 4); /* Creator Revision */
> --
> 2.31.1
>
>