On Fri, Nov 25, 2022 at 03:00:48PM +0800, Michael Chang via Grub-devel wrote: > On Thu, Nov 24, 2022 at 05:04:48PM +0100, Daniel Kiper wrote: > > On Mon, Oct 17, 2022 at 01:19:08PM +0800, Michael Chang via Grub-devel > > wrote: > > > On Fri, Oct 14, 2022 at 11:40:01AM +0200, Daniel Kiper wrote: > > > > On Fri, Oct 07, 2022 at 01:37:10PM +0800, Michael Chang via Grub-devel > > > > wrote: > > > > > This helps to prevent out of memory error when reading large files > > > > > via disabling > > > > > tpm device as verifier has to read all content into memory in one > > > > > chunk to > > > > > measure the hash and extend to tpm. > > > > > > > > How does this patch help when the TPM is present in the system? > > > > > > If the firmware menu offers option to disable TPM device, then this > > > patch can be useful to get around 'out of memory error' through > > > disabling TPM device from firmware in order to make tpm verifier won't > > > be in the way of reading huge files. > > > > > > This is essentially a compromised solution as long as tpm module can be > > > a built-in module in signed image and at the same time user may come > > > across the need to open huge files, for eg, loopback mount in grub for > > > the rescue image. In this case they could be opted in to disable tpm > > > device from firmware to proceed if they run into out of memory or other > > > (slow) reading issues. > > > > I think I would prefer something similar to this [1] patch. Of course > > if [1] is not enough... > > The tpm verifier attempts to set GRUB_VERIFY_FLAGS_SINGLE_CHUNK for all > incoming files, which gets loaded into memory in its entirety as an > duplicated copy to disk files. The overhead is too huge to some low > profile hardwares with smaller memory or when the boot path has to cover > very large files, hence the out of memory error. > > I think it inevitable to use GRUB_VERIFY_FLAGS_SINGLE_CHUNK as tpm > measures and extends file intergrity. But we ought to avoid the overhead > when TPM device is not present or disabled by the user. > > The patch [1] seems to deal with the tpm error which prevents a file > from being opened, which is orthogonal to the memory allocation issue in > the common verifier before tpm doing measurement.
This is what I expected. So, that is why I said "Of course if [1] is not enough..."... :-) Now I think it would be nice if TPM verifier is disabled when the TPM device is broken/disabled/... and/or somebody sets a separate environemnt variable in the GRUB. WDYT? Daniel [1] http://git.savannah.gnu.org/gitweb/?p=grub.git;a=commit;h=a4356538d03c5a5350790b6453b523fb9214c2e9 _______________________________________________ Grub-devel mailing list Grub-devel@gnu.org https://lists.gnu.org/mailman/listinfo/grub-devel