Re: [PATCH] x86/kprobes: Restore BTF if the single-stepping is cancelled

[Steven Rostedt <rostedt@goodmis.org>]

Did this patch fall through the cracks?

-- Steve


On Wed, 28 Oct 2020 23:31:10 +0900
Masami Hiramatsu <mhiramat@kernel.org> wrote:

> Fix to restore BTF if single-stepping causes a page fault and
> it is cancelled.
> 
> Usually the BTF flag was restored when the single stepping is done
> (in resume_execution()). However, if a page fault happens on the
> single stepping instruction, the fault handler is invoked and
> the single stepping is cancelled. Thus, the BTF flag is not
> restored.
> 
> Fixes: 1ecc798c6764 ("x86: debugctlmsr kprobes")
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> ---
>  arch/x86/kernel/kprobes/core.c |    5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
> index 547c7abb39f5..39f7d8c3c064 100644
> --- a/arch/x86/kernel/kprobes/core.c
> +++ b/arch/x86/kernel/kprobes/core.c
> @@ -937,6 +937,11 @@ int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
>  		 * So clear it by resetting the current kprobe:
>  		 */
>  		regs->flags &= ~X86_EFLAGS_TF;
> +		/*
> +		 * Since the single step (trap) has been cancelled,
> +		 * we need to restore BTF here.
> +		 */
> +		restore_btf();
>  
>  		/*
>  		 * If the TF flag was set before the kprobe hit,