[ Pulling in EDK2 folks for help ]
On Wed, 20 Aug, at 08:53:45PM, Michael Brown wrote:
> On 20/08/14 20:05, Mantas Mikulėnas wrote:
> >
> >I experimented with some things (like setting chunk size to a few kB
> >to see if it hangs earlier or only at the very end; etc.), and finally
> >found out that it stops freezing if I pad the initrd file to a
> >multiple of 512 bytes :/ That is, 5684268 bytes will freeze, 5684736
> >bytes will not.
> >
> >...In other words, seems like it cannot read chunks that aren't
> >multiples of 512 into a location above 4 GB. Or something like that...
>
> I haven't been following this thread closely, but that immediately
> sounds like a problem within the EFI_DISK_IO_PROTOCOL implementation
> (which is responsible for handling smaller-than-block-sized reads).
> Looking at the EDK2 implementation in
> MdeModulePkg/Universal/Disk/DiskIoDxe/DiskIo.c, the memory
> management does appear to be somewhat inventive. In particular,
> there's a frequent pattern in DiskIoCreateSubtaskList() equivalent
> to:
>
> if ( blocking_io ) {
> buffer = some_static_buffer;
> } else {
> buffer = malloc ( len );
> if ( ! buffer )
> goto single_shared_error_label;
> }
> ... do not record whether or not buffer was dynamically allocated ...
> ... use buffer as part of an asynchronous I/O operation ...
> ... eventually choose whether or not to free buffer, and hope the
> choice is correct ...
>
> It's not at all obvious that memory is freed correctly, especially
> under some of the error paths within that code.
>
> I can't immediately see anything that should fail with a pointer
> above 4G, but I wouldn't be surprised to find a path that causes a
> double free or similar error.
Guys, the original thread starts here,
http://article.gmane.org/gmane.linux.kernel.efi/4424
Basically, reading into a buffer above 0xffffffff using
EFI_FILE_PROTOCOL causes Mantas' machine to crash, irrespective of the
size of the read.
Is this a known issue? Perhaps here be dragons?
Halp?
--
Matt Fleming, Intel Open Source Technology Center
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