linux-hardening - Re: [PATCH v2 2/2] usercopy: Convert test_user

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Message-ID: <202406120927.3C64ACD6@keescook>
Date: Wed, 12 Jun 2024 09:51:52 -0700
From: Kees Cook <kees@...nel.org>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Mark Rutland <mark.rutland@....com>, David Gow <davidgow@...gle.com>,
	Vitor Massaru Iha <vitor@...saru.org>,
	Ivan Orlov <ivan.orlov0322@...il.com>,
	Brendan Higgins <brendan.higgins@...ux.dev>,
	Rae Moar <rmoar@...gle.com>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
	kunit-dev@...glegroups.com, linux-hardening@...r.kernel.org,
	linux-m68k@...ts.linux-m68k.org
Subject: Re: [PATCH v2 2/2] usercopy: Convert test_user_copy to KUnit test

On Wed, Jun 12, 2024 at 05:13:39PM +0800, David Gow wrote:
> On Tue, 11 Jun 2024 at 05:33, Kees Cook <kees@...nel.org> wrote:
> >
> > Convert the runtime tests of hardened usercopy to standard KUnit tests.
> >
> > Co-developed-by: Vitor Massaru Iha <vitor@...saru.org>
> > Signed-off-by: Vitor Massaru Iha <vitor@...saru.org>
> > Link: https://lore.kernel.org/r/20200721174654.72132-1-vitor@massaru.org
> > Tested-by: Ivan Orlov <ivan.orlov0322@...il.com>
> > Signed-off-by: Kees Cook <kees@...nel.org>
> > ---
> 
> This looks good, particularly with the x86 fix applied.
> 
> It's still hanging on m68k -- I think at the 'illegal reversed
> copy_to_user passed' test -- but I'll admit to not having tried to
> debug it further.
> 
> One other (set of) notes below about using KUNIT_EXPECT_MEMEQ_MSG(),
> otherwise (assuming the m68k stuff isn't actually a regression, which
> I haven't tested but I imagine is unlikely),

Hi Geert,

I'm trying to debug a hang on m68k in the usercopy behavioral testing
routines. It's testing for the pathological case of having inverted
arguments to copy_to_user():

        user_addr = kunit_vm_mmap(test, NULL, 0, priv->size,
                            PROT_READ | PROT_WRITE | PROT_EXEC,
                            MAP_ANONYMOUS | MAP_PRIVATE, 0);
	...
	bad_usermem = (char *)user_addr;
	...
	KUNIT_EXPECT_NE_MSG(test, copy_to_user((char __user *)kmem, bad_usermem,
					       PAGE_SIZE), 0,
		"illegal reversed copy_to_user passed");

On other architectures, this immediate fails because the access_ok()
check rejects it. On m68k with CONFIG_ALTERNATE_USER_ADDRESS_SPACE,
access_ok() short-circuits to "true". I've tried reading
arch/m68k/include/asm/uaccess.h but I'm not sure what's happening under
CONFIG_CPU_HAS_ADDRESS_SPACES.

For now I've excluded that test for m68k, but I'm not sure what's
expected to happen here on m68k for this set of bad arguments. Can you
advise?

Thanks!

-Kees

-- 
Kees Cook