Re: [PATCH v3 4/4] acpi: Set proper maximum size for "etc/acpi/rsdp" blob

[Igor Mammedov]

On Thu,  4 Mar 2021 11:55:54 +0100
David Hildenbrand <david@redhat.com> wrote:

> Let's also set a maximum size for "etc/acpi/rsdp", so the maximum
> size doesn't get implicitly set based on the initial table size. In my
> experiments, the table size was in the range of 22 bytes, so a single
> page (== what we used until now) seems to be good enough.
> 
> Now that we have defined maximum sizes for all currently used table types,
> let's assert that we catch usage with new tables that need a proper maximum
> size definition.
> 
> Also assert that our initial size does not exceed the maximum size; while
> qemu_ram_alloc_internal() properly asserts that the initial RAMBlock size
> is <= its maximum size, the result might differ when the host page size
> is bigger than 4k.
> 
> Suggested-by: Laszlo Ersek <lersek@redhat.com>
> Cc: Alistair Francis <alistair.francis@xilinx.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: "Michael S. Tsirkin" <mst@redhat.com>
> Cc: Igor Mammedov <imammedo@redhat.com>
> Cc: Peter Maydell <peter.maydell@linaro.org>
> Cc: Shannon Zhao <shannon.zhaosl@gmail.com>
> Cc: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Richard Henderson <richard.henderson@linaro.org>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  hw/acpi/utils.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/acpi/utils.c b/hw/acpi/utils.c
> index f2d69a6d92..0c486ea29f 100644
> --- a/hw/acpi/utils.c
> +++ b/hw/acpi/utils.c
> @@ -29,14 +29,19 @@
>  MemoryRegion *acpi_add_rom_blob(FWCfgCallback update, void *opaque,
>                                  GArray *blob, const char *name)
>  {
> -    uint64_t max_size = 0;
> +    uint64_t max_size;
[...]
> +    } else {
> +        g_assert_not_reached();
>      }
> +    g_assert(acpi_data_len(blob) <= max_size);

though it's correct,
but theoretically compiler might get unhappy about uninitialized max_size here

though if it compiles fine with our current CI it should be good enough

>  
>      return rom_add_blob(name, blob->data, acpi_data_len(blob), max_size, -1,
>                          name, update, opaque, NULL, true);