See my previous emails... and a couple of other nits.
On 07/31, Sebastian Andrzej Siewior wrote:
>
> +static int insn_is_popf(const u8 *insn)
> +{
> + /* popf */
> + if (insn[0] == 0x9d)
> + return 1;
> + return 0;
> +}
I can't believe I am going to blame the naming ;)
But "insn_is_popf" looks confusing, imho. Yes, currently "iret" can't
be probed, so (afaics) we only need to check "popf". Still I think the
name should be generic, and the comment should explain that only "popf"
can be probed. And I think it would be better to pass auprobe, not
->insn. But this all is cosmetic.
> +void arch_uprobe_enable_step(struct task_struct *child,
> + struct arch_uprobe *auprobe)
> +{
> + struct uprobe_task *utask = child->utask;
> + struct arch_uprobe_task *autask = &utask->autask;
> + struct pt_regs *regs = task_pt_regs(child);
> + unsigned long debugctl;
> +
> + autask->restore_flags = 0;
> + if (!(regs->flags & X86_EFLAGS_TF) &&
> + !insn_is_popf(auprobe->insn)) {
> + autask->restore_flags |= UPROBE_CLEAR_TF;
This looks correct, but
> + debugctl = get_debugctlmsr();
> + if (debugctl & DEBUGCTLMSR_BTF) {
No, I don't think "X86_EFLAGS_TF && !insn_is_popf" is right. I guess
this mimics "enable_single_step(child) && block" in enable_step(), but
we can't trust insn_is_popf(), we should check/clear DEBUGCTLMSR_BTF
unconditionally.
And get_debugctlmsr() is another reason why arch_uprobe_enable_step()
should not have "struct task_struct *child" argument, otherwise the
code looks confusing.
However, I am not sure we can trust it. We are in kernel mode,
DEBUGCTLMSR_BTF can be cleared by kprobes (Ananth, please correct me).
I think we need to check TIF_BLOCKSTEP.
Oleg.
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