Re: KUEP broken on FSP2?

[Eddie James <eajames@linux.ibm.com>]

On 10/6/23 00:21, Christophe Leroy wrote:
> Hi,
>
> Le 05/10/2023 à 21:06, Eddie James a écrit :
>> Hi,
>>
>> I'm attempting to run linux 6.1 on my FSP2, but my kernel crashes
>> attempting to get into userspace. The init script works, but the first
>> binary (mount) I run results in oops. Can anyone help me to debug this
>> further or suggest anything?
> I can't see anything in your dump suggesting that KUEP is broken, can you ?
>
> What I see is that kernel tries to execute user memory, which is wrong.
> And KUEP perfectly works by blocking that access. There is no call
> trace, suggesting that the kernel has jumped in the weed.


Right, the function works as intended, but the fact remains that I can't 
call anything in userspace (except init) without the kernel trying to 
execute that memory. I saw KUEP in the commit history and it seemed 
relevant, but I could certainly be mistaken. Can anyone think of 
anything else that might cause this? Or how I can debug further?


I went ahead and removed the couple of lines of assembly that enabled 
KUEP on 44x and tried again. Now I get a crash in load_elf_binary. NIP 
is the kfree(elf_phdata) and LR is garbage, so not entirely sure where 
it actually crashed...


Thanks,

Eddie


>
> Christophe
>
>>
>> Thanks,
>>
>> Eddie
>>
>>
>> [    1.042743] kernel tried to execute user page (b7ee2000) - exploit
>> attempt? (
>> uid: 0)
>> [    1.042846] BUG: Unable to handle kernel instruction fetch
>> [    1.042919] Faulting instruction address: 0xb7ee2000
>> [    1.042986] Oops: Kernel access of bad area, sig: 11 [#1]
>> [    1.043059] BE PAGE_SIZE=4K FSP-2
>> [    1.043106] Modules linked in:
>> [    1.043149] CPU: 0 PID: 61 Comm: mount Not tainted
>> 6.1.55-d23900f.ppcnf-fsp2
>> #1
>> [    1.043249] Hardware name: ibm,fsp2 476fpe 0x7ff520c0 FSP-2
>> [    1.043323] NIP:  b7ee2000 LR: 8c008000 CTR: 00000000
>> [    1.043392] REGS: bffebd83 TRAP: 0400   Not tainted
>> (6.1.55-d23900f.ppcnf-fs
>> p2)
>> [    1.043491] MSR:  00000030 <IR,DR>  CR: 00001000  XER: 20000000
>> [    1.043579]
>> [    1.043579] GPR00: c00110ac bffebe63 bffebe7e bffebe88 8c008000
>> 00001000 0000
>> 0d12 b7ee2000
>> [    1.043579] GPR08: 00000033 00000000 00000000 c139df10 48224824
>> 1016c314 1016
>> 0000 00000000
>> [    1.043579] GPR16: 10160000 10160000 00000008 00000000 10160000
>> 00000000 1016
>> 0000 1017f5b0
>> [    1.043579] GPR24: 1017fa50 1017f4f0 1017fa50 1017f740 1017f630
>> 00000000 0000
>> 0000 1017f4f0
>> [    1.044101] NIP [b7ee2000] 0xb7ee2000
>> [    1.044153] LR [8c008000] 0x8c008000
>> [    1.044204] Call Trace:
>> [    1.044238] Instruction dump:
>> [    1.044279] XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX
>> XXXXXXXX XX
>> XXXXXX
>> [    1.044392] XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX
>> XXXXXXXX XX
>> XXXXXX
>> [    1.044506] ---[ end trace 0000000000000000 ]---
>> [    1.044568]
>> [    1.044590] note: mount[61] exited with irqs disabled
>>