Date: Wed, 10 Jan 2018 09:25:20 -0600 (CST)
From: Christopher Lameter <cl@linux.com>
To: Kees Cook <keescook@chromium.org>
cc: linux-kernel@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        David Windsor <dave@nullcore.net>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andy Lutomirski <luto@kernel.org>,
        Christoph Hellwig <hch@infradead.org>,
        "David S. Miller" <davem@davemloft.net>,
        Laura Abbott <labbott@redhat.com>,
        Mark Rutland <mark.rutland@arm.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Christoffer Dall <christoffer.dall@linaro.org>,
        Dave Kleikamp <dave.kleikamp@oracle.com>,
        Jan Kara <jack@suse.cz>,
        Luis de Bethencourt <luisbg@kernel.org>,
        Marc Zyngier <marc.zyngier@arm.com>,
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Subject: Re: [PATCH 02/36] usercopy: Include offset in overflow report
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On Tue, 9 Jan 2018, Kees Cook wrote:

> -static void report_usercopy(unsigned long len, bool to_user, const char *type)
> +int report_usercopy(const char *name, const char *detail, bool to_user,
> +		    unsigned long offset, unsigned long len)
>  {
> -	pr_emerg("kernel memory %s attempt detected %s '%s' (%lu bytes)\n",
> +	pr_emerg("kernel memory %s attempt detected %s %s%s%s%s (offset %lu, size %lu)\n",
>  		to_user ? "exposure" : "overwrite",
> -		to_user ? "from" : "to", type ? : "unknown", len);
> +		to_user ? "from" : "to",
> +		name ? : "unknown?!",
> +		detail ? " '" : "", detail ? : "", detail ? "'" : "",
> +		offset, len);
>  	/*
>  	 * For greater effect, it would be nice to do do_group_exit(),
>  	 * but BUG() actually hooks all the lock-breaking and per-arch
>  	 * Oops code, so that is used here instead.
>  	 */
>  	BUG();

Should this be a WARN() or so? Or some configuration that changes
BUG() behavior? Otherwise

> +
> +	return -1;

This return code will never be returned.

Why a return code at all? Maybe I will see that in the following patches?