Re: [PATCH] kprobes/x86: Use copy_from_kernel_nofault() to read from unsafe address

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

On Fri, 15 Mar 2024 00:12:30 +0900
"Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote:

> From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> 
> Read from an unsafe address with copy_from_kernel_nofault() in
> arch_adjust_kprobe_addr() because this function is used before checking
> the address is in text or not. Syzcaller bot found a bug and reported
> the case if user specifies inaccessible data area,
> arch_adjust_kprobe_addr() will cause a kernel panic.
> 
> 
> Reported-by: Qiang Zhang <zzqq0103.hey@gmail.com>
> Closes: https://lore.kernel.org/all/CAKHoSAs2rof6vQVBw_Lg_j3QNku0CANZR2qmy4eT7R5Lo8MFbg@mail.gmail.com/
> Fixes: cc66bb914578 ("x86/ibt,kprobes: Cure sym+0 equals fentry woes")
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> ---
>  arch/x86/kernel/kprobes/core.c |   11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
> index a0ce46c0a2d8..a885eea3bd34 100644
> --- a/arch/x86/kernel/kprobes/core.c
> +++ b/arch/x86/kernel/kprobes/core.c
> @@ -335,7 +335,16 @@ static int can_probe(unsigned long paddr)
>  kprobe_opcode_t *arch_adjust_kprobe_addr(unsigned long addr, unsigned long offset,
>  					 bool *on_func_entry)
>  {
> -	if (is_endbr(*(u32 *)addr)) {
> +	u32 insn;
> +
> +	/*
> +	 * Since addr is not guaranteed to be safely accessed yet, use
> +	 * copy_from_kernel_nofault() to get the instruction.
> +	 */
> +	if (copy_from_kernel_nofault(&insn, (void *)addr, sizeof(u32)))
> +		return 0;

Oops, it should be NULL.

> +
> +	if (is_endbr(insn)) {
>  		*on_func_entry = !offset || offset == 4;
>  		if (*on_func_entry)
>  			offset = 4;
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>