Re: [PATCH v2 3/6] powerpc/32s: Only leave NX unset on segments used for modules

From: Christophe Leroy
Date: Fri Aug 21 2020 - 01:11:50 EST




Le 21/08/2020 à 00:00, Andreas Schwab a écrit :
On Jun 29 2020, Christophe Leroy wrote:

Instead of leaving NX unset on all segments above the start
of vmalloc space, only leave NX unset on segments used for
modules.

I'm getting this crash:

kernel tried to execute exec-protected page (f294b000) - exploit attempt (uid: 0)
BUG: Unable to handle kernel instruction fetch
Faulting instruction address: 0xf294b000
Oops: Kernel access of bad area, sig: 11 [#1]
BE PAGE_SIZE=4K MMU=Hash PowerMac
Modules linked in: pata_macio(+)
CPU: 0 PID: 87 Comm: udevd Not tainted 5.8.0-rc2-test #49
NIP: f294b000 LR: 0005c60 CTR: f294b000
REGS: f18d9cc0 TRAP: 0400 Not tainted (5.8.0-rc2-test)
MSR: 10009032 <E,ME,IR,DR,RI> CR: 84222422 XER: 20000000
GPR00: c0005c14 f18d9d78 ef30ca20 00000000 ef0000e0 c00993d0 ef6da038 0000005e
GPR08: c09050b8 c08b0000 00000000 f18d9d78 44222422 10072070 00000000 0fefaca4
GPR16: 1006a00c f294d50b 00000120 00000124 c0096ea8 0000000e ef2776c0 ef2776e4
GPR24: f18fd6e8 00000001 c086fe64 c086fe04 00000000 c08b0000 f294b000 ffffffff
NIP [f294b000] pata_macio_init+0x0/0xc0 [pata_macio]
LR [c0005c60] do_one_initcall+0x6c/0x160
Call Trace:
[f18d9d78] [c0005c14] do_one_initcall+0x20/0x160 (unreliable)
[f18d9dd8] [c009a22c] do_init_module+0x60/0x1c0
[f18d9df8] [c00993d8] load_module+0x16a8/0x1c14
[f18d9ea8] [c0099aa4] sys_finit_module+0x8c/0x94
[f18d9f38] [c0012174] ret_from_syscall+0x0/0x34
--- interrupt: c01 at 0xfdb4318
LR = 0xfeee9c0
Instruction dump:
XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX
XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX <3d20c08b> 3d40c086 9421ffe0 8129106c
---[ end trace 85a98cc836109871 ]---


Please try the patch at https://patchwork.ozlabs.org/project/linuxppc-dev/patch/07884ed033c31e074747b7eb8eaa329d15db07ec.1596641219.git.christophe.leroy@xxxxxxxxxx/

And if you are using KAsan, also take https://patchwork.ozlabs.org/project/linuxppc-dev/patch/6eddca2d5611fd57312a88eae31278c87a8fc99d.1596641224.git.christophe.leroy@xxxxxxxxxx/

Allthough I have some doubt that it will fix it, because the faulting instruction address is at 0xf294b000 which is within the vmalloc area. In the likely case the patch doesn't fix the issue, can you provide your .config and a dump of /sys/kernel/debug/powerpc/segment_registers (You have to have CONFIG_PPC_PTDUMP enabled for that) and also the below part from boot log.

[ 0.000000] Memory: 509556K/524288K available (7088K kernel code, 592K rwdata, 1304K rodata, 356K init, 803K bss, 14732K reserved, 0K cma-reserved)
[ 0.000000] Kernel virtual memory layout:
[ 0.000000] * 0xff7ff000..0xfffff000 : fixmap
[ 0.000000] * 0xff7fd000..0xff7ff000 : early ioremap
[ 0.000000] * 0xe1000000..0xff7fd000 : vmalloc & ioremap


Thanks
Christophe