Break or trivialize recovery mode

Question

Is it possible to have either a broken recovery mode (without bricking other modes) or a trivial recovery mode (e.g. no menu and automatically shutdown)? Where can I find existing ones or instructions to build my own one?

One naive "solution" I thought about is to flash 0 into /recovery, but I do not know if there may be unexpected consequences.

The main problem of flashing a broken recovery is that someone can reflash a working recovery using the same method. Therefore this only an obstacle for "very simple Android users". — Robert, Jun 28 '21 at 08:19
@Robert I understand that. But exposing a 3-second factory reset option to everyone is even worse. Also, let's ignore FRP since that relies on google services. — SmoothKen, Jun 28 '21 at 08:35
Does this answer your question? Is Android's system recovery a firmware thing or Android thing? Can factory reset be prevented? — alecxs, Jun 29 '21 at 06:52
@alecxs The answer in that question says " In A/B slots, recovery is part of boot.img so it can be directly booted by ABL." If I understand correctly normal boot and recovery do share the same kernel. But then where is the beginning of the railroad switch? in ramdisk? — SmoothKen, Jun 29 '21 at 10:17
that happens earlier. in ABL where the physical key is recognized. — alecxs, Jun 30 '21 at 07:10
@alecxs Ok key gets recognized. But suppose we are not on A-only device, the same kernel will be loaded. So there is going to be a firmware level railroad switch? Do recovery and normal os use the same ramdisk? — SmoothKen, Jun 30 '21 at 14:09
https://source.android.com/devices/bootloader/partitions/ramdisk-partitions — alecxs, Jun 30 '21 at 15:23
@alecxs No I am not mixing them up but that link clarifies a bit. Do we have control over kernel parameters or it is completely hardcoded in bootloader? — SmoothKen, Jul 01 '21 at 02:56
use this tool AIK to separate ramdisk from kernel and have a look into split_img/cmdline txt file for parameters — alecxs, Jul 01 '21 at 06:19

Break or trivialize recovery mode

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