Re: [edk2-devel] [PATCH] OvmfPkg/VirtioFsDxe: tolerate opening an abs. pathname rel. to a reg. file

["Laszlo Ersek" <lersek@redhat.com>]

On 10/19/23 08:28, Gerd Hoffmann wrote:
> On Wed, Oct 18, 2023 at 07:24:34PM +0200, Laszlo Ersek wrote:
>> Referring to a file relative to a regular file makes no sense (or at least
>> it cannot be implemented consistently with how a file is referred to
>> relative to a directory). VirtioFsSimpleFileOpen() has enforced this
>> strictly since the beginning, and a few months ago I reported USWG Mantis
>> ticket #2367 [1] too, for clearing up the related confusion in the UEFI
>> spec.
>>
>> Unfortunately, the shim boot loader contains such a bug [2] [3]. I don't
>> believe the shim bug is ever going to be fixed. We can however relax the
>> check in VirtioFsSimpleFileOpen() a bit: if the pathname that's being
>> opened relative to a regular file is absolute, then the base file is going
>> to be ignored anyway, so we can let the caller's bug slide. This happens
>> to make shim work.
>>
>> Why this matters: UEFI-bootable Linux installer ISOs tend to come with
>> shim and grub in the embedded (ElTorito) FAT image (ESP). Sometimes you
>> want to build upstream shim/grub binaries, but boot the same ISO
>> otherwise. The fastest way for overriding the ESP for this purpose is to
>> copy its original contents to a virtio filesystem, then overwrite the shim
>> and grub binaries from the host side. Note that this is different from
>> direct-booting a kernel (via fw_cfg); the point is to check whether the
>> just-built shim and grub are able to boot the rest of the ISO.
>>
>> [1] https://mantis.uefi.org/mantis/view.php?id=2367
>> [2] https://bugzilla.redhat.com/show_bug.cgi?id=1966973
>> [3] https://github.com/rhboot/shim/issues/382
>>
>> Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
>> Cc: Gerd Hoffmann <kraxel@redhat.com>
>> Cc: Jiewen Yao <jiewen.yao@intel.com>
>> Cc: Jordan Justen <jordan.l.justen@intel.com>
>> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
> 
> Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>
> Tested-by: Gerd Hoffmann <kraxel@redhat.com>

Merged via <https://github.com/tianocore/edk2/pull/4930>; commit
8abbf6d87e68.

Thanks!
Laszlo



-=-=-=-=-=-=-=-=-=-=-=-
Groups.io Links: You receive all messages sent to this group.
View/Reply Online (#109804): https://edk2.groups.io/g/devel/message/109804
Mute This Topic: https://groups.io/mt/102044004/7686176
Group Owner: devel+owner@edk2.groups.io
Unsubscribe: https://edk2.groups.io/g/devel/leave/12367111/7686176/1913456212/xyzzy [rebecca@openfw.io]
-=-=-=-=-=-=-=-=-=-=-=-