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Old 05-14-2022, 06:23 AM   #16
jhowell
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Originally Posted by j.p.s View Post
Good idea. I hope someone looks into this. It might be a bit more complicated than just putting in a large number.
One thing to consider is that Kindles report the build number to Amazon and that controls how the server interacts with the device. Putting in an incorrect value may cause problems and also advertise to Amazon that the device is jail broken.
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Old 05-15-2022, 02:13 PM   #17
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One thing to consider is that Kindles report the build number to Amazon and that controls how the server interacts with the device. Putting in an incorrect value may cause problems and also advertise to Amazon that the device is jail broken.
Too bad, since it would have been a simple way to block unwanted updates.

But going in the other direction (lower version number), could this be a way to block KFX delivery? (possibly subject to constraint of lowest version ever available for a particular model)
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Old 05-15-2022, 02:31 PM   #18
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Wiping (at least) some of the more database-y stuff from /var/local might be a good idea before attempting a significant (or maybe even a not so significant one) downgrade, because nothing in the process is intended to support database downgrades .

IIRC, back in the olden days, at worst it just broke stuff at runtime, but there is a non-zero chance it could break the boot, which would be bad .
Maybe the contents of the .sdr directories for books might be troublesome as well?
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Old 05-15-2022, 08:21 PM   #19
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Originally Posted by j.p.s View Post
But going in the other direction (lower version number), could this be a way to block KFX delivery? (possibly subject to constraint of lowest version ever available for a particular model)
As a test on my PW3 I changed version.txt to indicate the build of the initial release firmware version (5.6.1.1 build 2634130033) that predates KFX format. After rebooting I downloaded a book that had previously been on the Kindle in KFX format and it downloaded in KF8 format instead.

Unfortunately the user interface of the Kindle became seriously messed up and unusable, with a mix of old and new UI elements. The top drop down menu could not be activated. Library view disappeared. After opening a book it was impossible to close it through the UI.

I finally restored the version number and did a factory reset to make it usable again.

Update: It appears that during my testing the Kindle "updated" itself to version 5.13.7 which was an older version than was actually running on the device. That may have been the actual cause of the UI failure. I recommend that anyone setting a fake build version should block OTA updates first.

Last edited by jhowell; 05-15-2022 at 09:19 PM.
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Old 05-16-2022, 03:03 AM   #20
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Hmm, wasn't the factory image for PW3 5.6.5 and 5.6.1.1 the last available firmware update for PW1??
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Old 05-16-2022, 03:18 AM   #21
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Do you think that there is any possibility to fake build number in original update file to downgrade firmware without jailbreak?
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Old 05-16-2022, 07:48 AM   #22
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Hmm, wasn't the factory image for PW3 5.6.5 and 5.6.1.1 the last available firmware update for PW1??
No and Yes. It is true that 5.6.1.1 was the last firmware version for the PW1. However the original PW3 release was also 5.6.1.1. The first update was version 5.6.5 and came out very quickly with support for Enhanced Typesetting (KFX format). See the thread PW3 - First Look.

You can see the full list of firmware versions for each Kindle model on Amazon's Source Code Notice page. For the PW3 (7th Generation) released in 2015 the original firmware version (last on the list) was Kindle_src_5.6.1.1_2634130033.tar.gz.
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Old 05-16-2022, 07:53 AM   #23
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Do you think that there is any possibility to fake build number in original update file to downgrade firmware without jailbreak?
No. Firmware updates are cryptographically signed by Amazon and will not be installed if altered.
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Old 05-16-2022, 08:25 AM   #24
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Ok, then my PW3 must have come with 5.6.5 installed when I've bought it in August 2015. I definitely didn't install a firmware update before jailbreak-ing it and I've definitely used @Branch Delay's jailbreak exploit.

It is interesting how there is no source code posted for PW5's 5.14.0.1

Last edited by shamanNS; 05-16-2022 at 08:30 AM.
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Old 05-16-2022, 03:10 PM   #25
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Ok, then my PW3 must have come with 5.6.5 installed when I've bought it in August 2015.
You need to talk to yourself in 2015

https://www.mobileread.com/forums/sh...5&postcount=12
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Old 05-16-2022, 03:27 PM   #26
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As a test on my PW3 I changed version.txt to indicate the build of the initial release firmware version (5.6.1.1 build 2634130033) that predates KFX format. After rebooting I downloaded a book that had previously been on the Kindle in KFX format and it downloaded in KF8 format instead.
Thanks.

Does the book have images? If so, were they in an azw6 file, or was everything in the azw3?

Quote:
Unfortunately the user interface of the Kindle became seriously messed up and unusable, with a mix of old and new UI elements. The top drop down menu could not be activated. Library view disappeared. After opening a book it was impossible to close it through the UI.
That's too bad. I hope it didn't leave any lasting problems.

I can see why they would use version number to select download type and why it would be attractive to use to block downgrades. But it seems it would be a prime generator of new bugs and strange side effects to have it affect UI. I wonder how many lines they have to tweak every time the version changes solely because of this.

Quote:
I finally restored the version number and did a factory reset to make it usable again.

Update: It appears that during my testing the Kindle "updated" itself to version 5.13.7 which was an older version than was actually running on the device. That may have been the actual cause of the UI failure. I recommend that anyone setting a fake build version should block OTA updates first.
Yes, I think that's pretty much a requitrement for this kind of research.

Thanks for being a pioneer and risking the arrows.
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Old 05-16-2022, 03:36 PM   #27
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Funny note: if u want block ANY updates(even via reboot) - type 999999 in build number
BE CAREFUL!Do it only if u have SSH access to device and u know root password
DO NOT RESET DEVICE AFTER THAT!
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Old 05-16-2022, 03:46 PM   #28
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Funny note: if u want block ANY updates(even via reboot) - type 999999 in build number
BE CAREFUL!Do it only if u have SSH access to device and u know root password
DO NOT RESET DEVICE AFTER THAT!
That (more or less) was already suggested by fonix and warned against by jhowell
because of effects on server interaction (file type delivered, etc). And recent results show that the UI can be affected.

Quote:
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Okay, I'm excited about this, but for a completely different reason...

I believe by modifying the build values here, one could essentially block firmware updates completely (at least until Amazon catches up with the version number supplied), essentially making sure that your jailbreak doesn't get wiped out because Amazon forced an update even though you turned off auto updates.
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One thing to consider is that Kindles report the build number to Amazon and that controls how the server interacts with the device. Putting in an incorrect value may cause problems and also advertise to Amazon that the device is jail broken.
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Old 05-16-2022, 04:04 PM   #29
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Does the book have images? If so, were they in an azw6 file, or was everything in the azw3?
Everything was in the AZW3 file. I wouldn't expect anything else since the only image in that book is the cover. I didn't try any image-heavy books.

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I can see why they would use version number to select download type and why it would be attractive to use to block downgrades. But it seems it would be a prime generator of new bugs and strange side effects to have it affect UI. I wonder how many lines they have to tweak every time the version changes solely because of this.
I don't think the change to the build number actually impacted the UI. I didn't realize at first that the firmware had updated itself to an older version than the one already installed. That resulted in a lot of incompatible data files. Because they do not expect downgrades the firmware does not handle them at all gracefully.

Putting a DO_FACTORY_RESTORE file in /mnt/us and rebooting cleaned it up.
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Old 05-16-2022, 04:22 PM   #30
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That (more or less) was already suggested by fonix and warned against by jhowell
because of effects on server interaction (file type delivered, etc).
Kindle apps and devices include the build number in normal interactions with Amazon's servers. They keep track of the most recent build announced by each registered device. That in turn controls a large set of capabilities associated with the device.

I don't know how Amazon treats interactions with a device reporting an unexpected build number. They might retain the capabilities associated with last valid build number received or switch to a default set. In any case it is likely to be reported in an error log somewhere.

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And recent results show that the UI can be affected.
Actually I now believe that the UI problem was due to the unexpected firmware downgrade.
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