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SubjectRe: [PATCH v2] powerpc/kprobes: Fix Oops by passing ppc_inst as a pointer to emulate_step() on ppc32
Christophe Leroy wrote:
> From: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
>
> 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@vger.kernel.org
> Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
> ---
> v2: Rebased on powerpc/merge 7f030e9d57b8
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>

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

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