Invalid safety assumption in `SdtHeaderIterator`

[usadson]

The SdtHeaderIterator can be used to iterate over every SdtHeader, but the iterator only maps the size of the SdtHeader (36 bytes), whilst the validation requires that the whole header is mapped (for SSDTs this can be quite large, spanning over multiple pages).

This can be seen in acpi/src/lib.rs:503:

impl<H> Iterator for SdtHeaderIterator<'_, H>
where
    H: AcpiHandler,
{
    type Item = SdtHeader;

    fn next(&mut self) -> Option<Self::Item> {
        // ...

        // SAFETY: `address` needs to be valid for the size of `SdtHeader`, or the ACPI tables are malformed (not a
        // software issue).
        let header_mapping = unsafe {
            self.handler.map_physical_region::<SdtHeader>(table_phys_ptr as usize, mem::size_of::<SdtHeader>())
        };
        let r = header_mapping.validate(header_mapping.signature);

        // ...
    }
}

The last line calls SdtHeader::validate()

pub fn validate(&self, signature: Signature) -> AcpiResult<()> {
    self.validate_header_fields(signature)?;
    self.validate_checksum(signature)?;

    Ok(())
}

Which in turn calls SdtHeader::validate_checksum():

fn validate_checksum(&self, signature: Signature) -> AcpiResult<()> {
        // SAFETY: Entire table is mapped.
        let table_bytes =
            unsafe { core::slice::from_raw_parts((self as *const SdtHeader).cast::<u8>(), self.length as usize) };
        // ...
}

The SAFETY-assumption is that the entire table is mapped, whilst only the header was mapped.