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is it possible to downgrade SM-G950F?

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querty75

Member
Feb 13, 2013
23
1
Samsung Galaxy S8
Hello,
Is there a way to dowgrade the bootloader of SM-G950F with stock fw G950FXXUCDUD1 to further flash a stock fw Android 8?
- flashing a downgraded bl with twrp?
- with "combination" fw?
- with a modified stock bl flashed with Odin?
...?
Thank you!
 

querty75

Member
Feb 13, 2013
23
1
Samsung Galaxy S8
No.
Combination roms follow stock firmware regarding bootloader version ( can't downgrade). TWRP is a recovery image to replace stock, You can do more things in twrp over stock except downgrade stock firmware.
Ok, but what about this thread which seems to say it's doable with combination roms?
 

spawnlives

Senior Member
Jan 27, 2018
1,050
396
Samsung Galaxy S8
Samsung Galaxy S9
I've seen many guides on how to downgrade stock firmware. Most of them revolve around editing stock firmware. None of them mention whether the bootloader version was actually downgraded. To me personally you are essentially trying to install a custom type rom using by using stock firmware.
 

querty75

Member
Feb 13, 2013
23
1
Samsung Galaxy S8
I've seen many guides on how to downgrade stock firmware. Most of them revolve around editing stock firmware. None of them mention whether the bootloader version was actually downgraded. To me personally you are essentially trying to install a custom type rom using by using stock firmware.
I checked and you're right. The minimal configuration for flashing the bl is a tar with cm.bin and sboot.bin and this leads to the usual error "... check fail(cm) device : x binary : y" (whatever odin version used... patched or stock)
reverse engineering sboot and cm.bin and changing the binary release doesn't help because the code is signed and verified by the PBL from the ROM.
The only way to do it should be to connect to the exynos jtag / uart / ? and to reverse engineering the soc (!) modifying the way the PBL check the SBOOT.
Adam Outler a researcher did it on GalaxyS (1 or 2!) more than ten year ago... (https://forum.xda-developers.com/t/how-to-hack-hardware-binary-and-bend-it-to-your-will.1338073/)
So... I think is doable with a lot of talent and patience...
Anyway, thank you for your help!
 
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    No. Samsung will not allow flashing of lower bootloader versions numbers.
    1
    No.
    Combination roms follow stock firmware regarding bootloader version ( can't downgrade). TWRP is a recovery image to replace stock, You can do more things in twrp over stock except downgrade stock firmware.
    1
    I've seen many guides on how to downgrade stock firmware. Most of them revolve around editing stock firmware. None of them mention whether the bootloader version was actually downgraded. To me personally you are essentially trying to install a custom type rom using by using stock firmware.
    I checked and you're right. The minimal configuration for flashing the bl is a tar with cm.bin and sboot.bin and this leads to the usual error "... check fail(cm) device : x binary : y" (whatever odin version used... patched or stock)
    reverse engineering sboot and cm.bin and changing the binary release doesn't help because the code is signed and verified by the PBL from the ROM.
    The only way to do it should be to connect to the exynos jtag / uart / ? and to reverse engineering the soc (!) modifying the way the PBL check the SBOOT.
    Adam Outler a researcher did it on GalaxyS (1 or 2!) more than ten year ago... (https://forum.xda-developers.com/t/how-to-hack-hardware-binary-and-bend-it-to-your-will.1338073/)
    So... I think is doable with a lot of talent and patience...
    Anyway, thank you for your help!