On 2022-05-18 10:59, Stefan Agner wrote: > Some devices report a IoAlign value of 2, however seem to require a > buffer with higher alignment.
After releasing Home Assistant OS 8.0 publicly, some systems still refuse to boot even with this patch applied. See bug reports collected in this issue: https://github.com/home-assistant/operating-system/issues/1912 At least in one instance using block size alignment helped. I am going to change to block size aligned unconditionally, and see how that behaves in wider deployment. -- Stefan > > The UEFI specification is saying: "IoAlign values of 0 and 1 mean that > the buffer can be placed anywhere in memory. Otherwise, IoAlign must > be a power of 2, and the requirement is that the start address of a > buffer must be evenly divisible by IoAlign with no remainder." > > It seems that this got misinterpreted by some vendors assuming IoAlign > is 2^IoAlign. There is also such a hint in an example in earlier > versions of the Driver Writer's Guide: > ScsiPassThruMode.IoAlign = 2; // Data must be alligned on 4-byte boundary > > However, it is unsafe to just blindly align buffers by 2^IoAlign, as > this would lead to an overflow for systems which use block size > alignment (e.g. 512 bytes, for example U-Boot). > > Work around by using an alignment of at least BlockSize (typically 512 > bytes) in case alignment is requested. Also make sure that IoAlign is > still respected as per UEFI specification if a higher alignment than > block size is requested. > > Note: The problem has only noticed with compressed squashfs. It seems > that ext4 (and presumably other file system drivers) pass buffers with > a higher alignment already. > > Acked-by: Heinrich Schuchardt <xypron.g...@gmx.de> > Signed-off-by: Stefan Agner <ste...@agner.ch> > --- > grub-core/disk/efi/efidisk.c | 18 ++++++++++++++++-- > 1 file changed, 16 insertions(+), 2 deletions(-) > > diff --git a/grub-core/disk/efi/efidisk.c b/grub-core/disk/efi/efidisk.c > index 9e20af70e..c4eb4f4e7 100644 > --- a/grub-core/disk/efi/efidisk.c > +++ b/grub-core/disk/efi/efidisk.c > @@ -553,8 +553,22 @@ grub_efidisk_readwrite (struct grub_disk *disk, > grub_disk_addr_t sector, > d = disk->data; > bio = d->block_io; > > - /* Set alignment to 1 if 0 specified */ > - io_align = bio->media->io_align ? bio->media->io_align : 1; > + /* > + * If IoAlign is > 1, it should represent the required alignment. However, > + * some UEFI implementation on Intel NUC systems seem to use IoAlign=2 but > + * require 2^IoAlign. > + * Make sure to align to at least block size if IO alignment is required. > + */ > + if (bio->media->io_align > 1) > + { > + if (bio->media->io_align < bio->media->block_size) > + io_align = bio->media->block_size; > + else > + io_align = bio->media->io_align; > + } > + else > + io_align = 1; > + > num_bytes = size << disk->log_sector_size; > > if ((grub_addr_t) buf & (io_align - 1)) _______________________________________________ Grub-devel mailing list Grub-devel@gnu.org https://lists.gnu.org/mailman/listinfo/grub-devel
