Debian SID kernel doesn't boot on PowerBook 3400c

[Finn Thain]

On Fri, 6 Aug 2021, Christophe Leroy wrote:

> > > > > 
> > > > > Can you check if they DO NOT happen at preceding commit c16728835~
> > > > > 
> > > 
> > > $ git checkout c16728835~
> > > Previous HEAD position was c16728835eec powerpc/32: Manage KUAP in C
> > > HEAD is now at 0b45359aa2df powerpc/8xx: Create C version of kuap
> > > save/restore/check helpers
> > > $ git am ../message.mbox
> > > warning: Patch sent with format=flowed; space at the end of lines might be
> > > lost.
> > > Applying: powerpc/32: Dismantle EXC_XFER_STD/LITE/TEMPLATE
> > > $ cp ../dot-config-powermac-5.13 .config
> > > $ make ARCH=powerpc CROSS_COMPILE=powerpc-linux-gnu- -j4 clean
> > > olddefconfig vmlinux
> > > 
> > > Linux version 5.12.0-rc3-pmac-00077-gc9f6e8dd045
> > > 
> > > 3) PB 3400c
> > > Hangs at boot (Mac OS screen)
> > > 
> > > 4) Wallstreet
> > > X fails, errors in console log (different than test 2), see
> > > Wallstreet_console-2.txt.
> > > 
> > 
> > This log shows that the errors "xfce4-session[1775]: bus error (7)" and
> > "kernel BUG at arch/powerpc/kernel/interrupt.c:49!" happen prior to commit
> > c16728835eec ("powerpc/32: Manage KUAP in C").
> 
> As mentionned by Nic, this is due to r11 being cloberred. For the time being
> the only r11 clobber identified is the one I have provided a fix for. I'm
> wondering whether it was applied for all further tests or not.
> 

Your fix was applied to this build with "git am ../message.mbox".

> ...
> > > 
> > > > 
> > > > > Could you test with CONFIG_PPC_KUAP and CONFIG_PPC_KUAP_DEBUG
> > > ...
> > > 
> > > $scripts/config -e CONFIG_PPC_KUAP
> > > $ scripts/config -e CONFIG_PPC_KUAP_DEBUG
> > > $ make ARCH=powerpc CROSS_COMPILE=powerpc-linux-gnu- -j4 clean
> > > olddefconfig vmlinux
> > > $ grep CONFIG_PPC_KUAP .config
> > > CONFIG_PPC_KUAP=y
> > > CONFIG_PPC_KUAP_DEBUG=y
> > > 
> > > Linux version 5.12.0-rc3-pmac-00078-g5cac2bc3752
> > > 
> > > 9) PB 3400c
> > > Hangs at boot (Mac OS screen)
> > > 
> > > 10) Wallstreet
> > > X failed at first login, worked at second login, one error in console
> > > log ("BUG: Unable to handle kernel instruction fetch"), see
> > > Wallstreet_console-5.txt.
> > > 
> > 
> > One might expect to see "Kernel attempted to write user page (b3399774) -
> > exploit attempt?" again here (see c16728835eec build above) but instead
> > this log says "Oops: Kernel access of bad area, sig: 11".
> 
> Maybe the test should be done a second time. As r11 is garbage it may or 
> may not be a user address. If it is a user address the we get "Kernel 
> attempted to write user page". If it is a random kernel address, we 
> likely get "Kernel access of bad area" instead.
> 

Your fix was applied here also.