From: Linus Torvalds <torvalds@linux-foundation.org>
To: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Kees Cook <keescook@chromium.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Arnd Bergmann <arnd@arndb.de>, Jean Delvare <jdelvare@suse.de>
Subject: Re: [GIT PULL] gcc-plugins updates for v4.13-rc1
Date: Wed, 5 Jul 2017 14:35:08 -0700 [thread overview]
Message-ID: <CA+55aFyu=uLyVsp2jfpZVyk3yJTJbLs01br1DUt==2hqk-NN+g@mail.gmail.com> (raw)
In-Reply-To: <CAKv+Gu-2ZzUd0G5Ngn_pca2AjMP4f9SKAdpEP7U3pH3msZxg0g@mail.gmail.com>
On Wed, Jul 5, 2017 at 1:40 PM, Ard Biesheuvel
<ard.biesheuvel@linaro.org> wrote:
>
> So while I think it may be useful for robustness, to avoid erratic
> behavior or exploitable interactions between different parts of the
> code, my estimation is that it wouldn't make a great deal of
> difference, given that the logic that allows the compiler to 'see the
> real initialization' is the same logic that warns us if it is lacking,
> and so in a warning free build, no init sequences should have been
> emitted to begin with.
So the issue I think would be good to fix is perhaps best explained by
pseudo-code
int testfn(struct somestruct __user *p)
{
struct somestruct a;
initialize_struct(&a);
if (copy_to_user(p, &a, sizeof(a)))
return -EFAULT;
return 0;
}
which is obviously made-up code, but is not actually entirely unrealistic.
It's fairly common code in various ioctl-like functions, but also in
things like the "stat()" system call etc. The thing that initializes a
variable is not necessarily visible, and gcc can not warn about the
fact that "initialize_struct()" doesn't actually initialize all
fields.
Or even if it does initialize all the fields, what about the padding
bytes? That doesn't matter in most normal C programs, since by
definition the padding bytes aren't used, but for the kernel, it
*does* matter when they get copied outside the kernel.
Linus
next prev parent reply other threads:[~2017-07-05 21:35 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-05 5:05 [GIT PULL] gcc-plugins updates for v4.13-rc1 Kees Cook
2017-07-05 19:07 ` Linus Torvalds
2017-07-05 20:40 ` Ard Biesheuvel
2017-07-05 21:35 ` Linus Torvalds [this message]
2017-07-05 21:48 ` Arnd Bergmann
2017-07-05 21:52 ` Kees Cook
2017-07-05 21:56 ` Linus Torvalds
2017-07-05 22:27 ` Ard Biesheuvel
2017-07-05 22:39 ` Linus Torvalds
2017-07-05 22:41 ` Andrey Ryabinin
2017-07-05 21:12 ` Arnd Bergmann
2017-07-05 21:49 ` Kees Cook
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