linux-kernel - Re: [PATCH] fortify: Use WARN instead of BUG for now

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Date:   Wed, 26 Jul 2017 08:52:11 -0400
From:   Daniel Micay <danielmicay@...il.com>
To:     Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        David Howells <dhowells@...hat.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fortify: Use WARN instead of BUG for now

It should just be renamed from fortify_panic -> fortify_error, including
in arch/x86/boot/compressed/misc.c and arch/x86/boot/compressed/misc.c.
It can use WARN instead of BUG by with a 'default n', !COMPILE_TEST
option to use BUG again. Otherwise it needs to be patched downstream
when that's wanted.

I don't think splitting it is the right approach to improving the
runtime error handling. That only makes sense for the compile-time
errors due to the limitations of __attribute__((error)). Can we think
about that before changing it? Just make it use WARN for now.

The best debugging experience would be passing along the sizes and
having the fortify_error function convert that into nice error messages.
For memcpy(p, q, n), n can be larger than both the detected sizes of p
and q, not just either one. The error should just be saying the function
name and printing the copy size and maximum sizes of p and q. That's
going to increase the code size too but I think splitting it will be
worse and it goes in the wrong direction in terms of complexity. It's
going to make future extensions / optimization harder if it's split.