Re: Debian SID kernel doesn't boot on PowerBook 3400c

(Christophe, you've seen some of this before, however there are new 
results added at the end. I've Cc'd the mailing lists this time.)

On Wed, 4 Aug 2021, Stan Johnson wrote:

On 8/4/21 8:41 PM, Finn Thain wrote:

quoted

$ curl https://lore.kernel.org/lkml/9b64dde3-6ebd-b446-41d9-61e8cb0d8c39@csgroup.eu/raw (local)
../message.mbox

ok

$ sha1 ../message.mbox
SHA1 (../message.mbox) = 436ce0adf893c46c84c54607f73c838897caeeea

quoted

On Wed, 4 Aug 2021, Christophe Leroy wrote:

quoted

Can you check if they happen at commit c16728835

$ git checkout c16728835eec
Checking out files: 100% (20728/20728), done.
Note: checking out 'c16728835eec'.

You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by performing another checkout.

If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -b with the checkout command again. Example:

  git checkout -b <new-branch-name>

HEAD is now at c16728835eec powerpc/32: Manage KUAP in C
$ 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
$ strings vmlinux | fgrep 'Linux version'
Linux version 5.12.0-rc3-pmac-00078-geb51c431b81 (johnson@ThinkPad) (powerpc-linux-gnu-gcc (Debian 8.3.0-2) 8.3.0, GNU ld (GNU Binutils for Debian) 2.31.1) #1 SMP Wed Aug 4 21:50:47 MDT 2021

1) PB 3400c
Hangs at boot (Mac OS screen), no serial console output

2) Wallstreet
X fails, errors ("Kernel attempted to write user page", "BUG: Unable to
handle kernel instruction fetch"), see Wallstreet_console-1.txt.

The log shows that the error "Kernel attempted to write user page 
(b3399774) - exploit attempt?" happens after commit c16728835eec 
("powerpc/32: Manage KUAP in C").

quoted

quoted

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").

$ git checkout 0b45359aa2df
...
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-ge06b29ce146

5) PB 3400c
Hangs at boot (Mac OS screen)

6) Wallstreet
X failed (X login succeeded, but setting up desktop failed), errors in
console log, see Wallstreet_console-3.txt.

(No need for those two tests: it's exactly the same code and almost the 
same failure modes: "kernel BUG at arch/powerpc/kernel/interrupt.c:50".)

On Thu, 5 Aug 2021, Stan Johnson wrote:

On 8/5/21 12:47 AM, Finn Thain wrote:

quoted

On Wed, 4 Aug 2021, Christophe Leroy wrote:

quoted

Could you test without CONFIG_PPC_KUAP

...

$ git checkout c16728835eec
...
HEAD is now at c16728835eec powerpc/32: Manage KUAP in C
$ 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
$ scripts/config -d CONFIG_PPC_KUAP
$ make ARCH=powerpc CROSS_COMPILE=powerpc-linux-gnu- -j4 clean olddefconfig vmlinux
$ grep CONFIG_PPC_KUAP .config
# CONFIG_PPC_KUAP is not set

Linux version 5.12.0-rc3-pmac-00078-g5cac2bc3752

7) PB 3400c
Hangs at boot (Mac OS screen)

8) Wallstreet
Everything works, no errors (see Wallstreet_console-4.txt).

That would seem to implicate CONFIG_PPC_KUAP itself. (Note that all builds 
up until this one have CONFIG_PPC_KUAP=y.)

quoted

quoted

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".

BTW, this procedure could be made simpler and easier if I pushed git 
branches to a public repo for Stan to build, which included Christophe's 
fix plus hard-wired Kconfig changes. That way, the .config file could be 
held constant and the commit hash in the serial console log would be more 
meaningful.