linux-kernel - Re: [PATCH] ARM: kprobes: Fix false positive with FORTIFY

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Date:   Tue, 30 Oct 2018 13:40:27 -0400
From:   William Cohen <wcohen@...hat.com>
To:     Kees Cook <keescook@...omium.org>,
        Russell King <linux@...linux.org.uk>
Cc:     Laura Abbott <labbott@...hat.com>, linux-kernel@...r.kernel.org,
        Masami Hiramatsu <mhiramat@...nel.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] ARM: kprobes: Fix false positive with FORTIFY_SOURCE

On 10/22/18 5:30 AM, Kees Cook wrote:
> The arm compiler internally interprets an inline assembly label
> as an unsigned long value, not a pointer. As a result, under
> CONFIG_FORTIFY_SOURCE, the size of the array pointed to by an address
> of a label is 4 bytes, which was tripping the runtime checks. Instead,
> we can just cast the label (as done with the size calculations earlier)
> to avoid the problem.
> 
> Reported-by: William Cohen <wcohen@...hat.com>
> Fixes: 6974f0c4555e ("include/linux/string.h: add the option of fortified string.h functions")
> Cc: stable@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  arch/arm/probes/kprobes/opt-arm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm/probes/kprobes/opt-arm.c b/arch/arm/probes/kprobes/opt-arm.c
> index b2aa9b32bff2..2c118a6ab358 100644
> --- a/arch/arm/probes/kprobes/opt-arm.c
> +++ b/arch/arm/probes/kprobes/opt-arm.c
> @@ -247,7 +247,7 @@ int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *or
>  	}
>  
>  	/* Copy arch-dep-instance from template. */
> -	memcpy(code, &optprobe_template_entry,
> +	memcpy(code, (unsigned char *)optprobe_template_entry,
>  			TMPL_END_IDX * sizeof(kprobe_opcode_t));
>  
>  	/* Adjust buffer according to instruction. */
> 

The patch fixes the issue for kretprobes.  It looks good to me.

Thanks,

-Will