Re: [PATCH v2] powerpc/kprobes: Fix Oops by passing ppc_inst as a pointer to emulate_step() on ppc32
From: Naveen N. Rao
Date: Thu Jun 24 2021 - 07:00:08 EST
Christophe Leroy wrote:
From: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
Trying to use a kprobe on ppc32 results in the below splat:
BUG: Unable to handle kernel data access on read at 0x7c0802a6
Faulting instruction address: 0xc002e9f0
Oops: Kernel access of bad area, sig: 11 [#1]
BE PAGE_SIZE=4K PowerPC 44x Platform
Modules linked in:
CPU: 0 PID: 89 Comm: sh Not tainted 5.13.0-rc1-01824-g3a81c0495fdb #7
NIP: c002e9f0 LR: c0011858 CTR: 00008a47
REGS: c292fd50 TRAP: 0300 Not tainted (5.13.0-rc1-01824-g3a81c0495fdb)
MSR: 00009000 <EE,ME> CR: 24002002 XER: 20000000
DEAR: 7c0802a6 ESR: 00000000
<snip>
NIP [c002e9f0] emulate_step+0x28/0x324
LR [c0011858] optinsn_slot+0x128/0x10000
Call Trace:
opt_pre_handler+0x7c/0xb4 (unreliable)
optinsn_slot+0x128/0x10000
ret_from_syscall+0x0/0x28
The offending instruction is:
81 24 00 00 lwz r9,0(r4)
Here, we are trying to load the second argument to emulate_step():
struct ppc_inst, which is the instruction to be emulated. On ppc64,
structures are passed in registers when passed by value. However, per
the ppc32 ABI, structures are always passed to functions as pointers.
This isn't being adhered to when setting up the call to emulate_step()
in the optprobe trampoline. Fix the same.
Fixes: eacf4c0202654a ("powerpc: Enable OPTPROBES on PPC32")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
---
v2: Rebased on powerpc/merge 7f030e9d57b8
Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
Thanks for rebasing this!
I think git am drops everything after three dashes, so applying this
patch will drop your SOB. The recommended style (*) for adding a
changelog is to include it within [] before the second SOB.
- Naveen
(*) https://www.kernel.org/doc/html/latest/maintainer/modifying-patches.html