If you convey an object code work under this section in, or with, or specifically for use in, a User Product, and the conveying occurs as part of a transaction in which the right of possession and use of the User Product is transferred to the recipient in perpetuity or for a fixed term
This reads to me as saying that if you sell somebody a computer which contains a signed bootloader derived from GPLv3 code, you have to provide them with some means of installing a modified bootloader. Which is fine: you do that by means of the computer having an option whereby the user can tell it to trust their signing key as well as yours, and then you don't have to supply your own private key because it isn't required in order to install and execute modified versions.
If you're offering a Linux distribution for download (or on CDs) and expecting users to have got some hardware from elsewhere to install it on, it's difficult to see how you think this clause would apply at all.
no subject
This reads to me as saying that if you sell somebody a computer which contains a signed bootloader derived from GPLv3 code, you have to provide them with some means of installing a modified bootloader. Which is fine: you do that by means of the computer having an option whereby the user can tell it to trust their signing key as well as yours, and then you don't have to supply your own private key because it isn't required in order to install and execute modified versions.
If you're offering a Linux distribution for download (or on CDs) and expecting users to have got some hardware from elsewhere to install it on, it's difficult to see how you think this clause would apply at all.