On 2 Feb 2023, at 09:48, Björn Töpel <bjorn@xxxxxxxxxx> wrote:
>
> Guo Ren <guoren@xxxxxxxxxx> writes:
>
>> On Wed, Feb 1, 2023 at 5:40 PM Björn Töpel <bjorn@xxxxxxxxxx> wrote:
>>>
>>> guoren@xxxxxxxxxx writes:
>>>
>>>> From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
>>>>
>>>> The current kprobe would cause a misaligned load for the probe point.
>>>> This patch fixup it with two half-word loads instead.
>>>>
>>>> Fixes: c22b0bcb1dd0 ("riscv: Add kprobes supported")
>>>> Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
>>>> Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
>>>> Link: https://lore.kernel.org/linux-riscv/878rhig9zj.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
>>>> Reported-by: Bjorn Topel <bjorn.topel@xxxxxxxxx>
>>>> ---
>>>> arch/riscv/kernel/probes/kprobes.c | 4 +++-
>>>> 1 file changed, 3 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/arch/riscv/kernel/probes/kprobes.c b/arch/riscv/kernel/probes/kprobes.c
>>>> index 41c7481afde3..c1160629cef4 100644
>>>> --- a/arch/riscv/kernel/probes/kprobes.c
>>>> +++ b/arch/riscv/kernel/probes/kprobes.c
>>>> @@ -74,7 +74,9 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
>>>> return -EILSEQ;
>>>>
>>>> /* copy instruction */
>>>> - p->opcode = *p->addr;
>>>> + p->opcode = (kprobe_opcode_t)(*(u16 *)probe_addr);
>>>> + if (GET_INSN_LENGTH(p->opcode) == 4)
>>>> + p->opcode |= (kprobe_opcode_t)(*(u16 *)(probe_addr + 2))
>>>> << 16;
>>>
>>> Ugh, those casts. :-( What about the memcpy variant you had in the other
>>> thread?
>> The memcpy version would force load probe_addr + 2. This one would
>> save an lh operation. The code text guarantees half-word alignment. No
>> misaligned load happened. Second, kprobe wouldn't write the last half
>> of 32b instruction.
>
> Ok, something more readable, like:
>
> diff --git a/arch/riscv/kernel/probes/kprobes.c b/arch/riscv/kernel/probes/kprobes.c
> index f21592d20306..3602352ba175 100644
> --- a/arch/riscv/kernel/probes/kprobes.c
> +++ b/arch/riscv/kernel/probes/kprobes.c
> @@ -50,14 +50,16 @@ static void __kprobes arch_simulate_insn(struct kprobe *p, struct pt_regs *regs)
>
> int __kprobes arch_prepare_kprobe(struct kprobe *p)
> {
> - unsigned long probe_addr = (unsigned long)p->addr;
> + u16 *insn = (u16 *)p->addr;
>
> - if (probe_addr & 0x1)
> + if ((uintptr_t)insn & 0x1)
> return -EILSEQ;
>
> /* copy instruction */
> - p->opcode = *p->addr;
> -
> + p->opcode = *insn++;
> + if (GET_INSN_LENGTH(p->opcode) == 4)
> + p->opcode |= *insn << 16;
*insn gets promoted to int not unsigned so this is UB if bit 15 is set.
Jess
> +
> /* decode instruction */
> switch (riscv_probe_decode_insn(p->addr, &p->ainsn.api)) {
> case INSN_REJECTED: /* insn not supported */
>
>
> Björn
>
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