Le 20/05/2021 à 09:29, Naveen N. Rao a écrit :
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
I remember running some kprobe tests before submitting the patch, how did I
miss that ?
Is there anything special to do to activate the use of optprobes and/or to hit
this bug ?
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.
Yes, and that was one of the reasons I was reluctant to that new 'struct ppc_inst', as it means
stack frames, copies, etc ... whereas we could have just changed it from 'unsigned int' to 'unsigned
long'.
Ok, now we have it, so let's use it, but use it correctly, see my clean-up series
https://patchwork.ozlabs.org/project/linuxppc-dev/list/?series=244719&state=* (v2 on the way).
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")
Signed-off-by: Naveen N. Rao <naveen.n....@linux.vnet.ibm.com>
---
arch/powerpc/kernel/optprobes.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/kernel/optprobes.c b/arch/powerpc/kernel/optprobes.c
index cdf87086fa33a0..2bc53fa48a1b33 100644
--- a/arch/powerpc/kernel/optprobes.c
+++ b/arch/powerpc/kernel/optprobes.c
@@ -281,8 +281,12 @@ int arch_prepare_optimized_kprobe(struct optimized_kprobe
*op, struct kprobe *p)
/*
* 3. load instruction to be emulated into relevant register, and
*/
- temp = ppc_inst_read((struct ppc_inst *)p->ainsn.insn);
- patch_imm_load_insns(ppc_inst_as_ulong(temp), 4, buff + TMPL_INSN_IDX);
+ if (IS_ENABLED(CONFIG_PPC64)) {
+ temp = ppc_inst_read((struct ppc_inst *)p->ainsn.insn);
+ patch_imm_load_insns(ppc_inst_as_ulong(temp), 4, buff +
TMPL_INSN_IDX);
+ } else {
+ patch_imm_load_insns((unsigned long)p->ainsn.insn, 4, buff +
TMPL_INSN_IDX);
+ }
It means commit https://github.com/linuxppc/linux/commit/693557ebf407a85ea400a0b501bb97687d8f4856
was not necessary and may be reverted.
Christophe
