Re: [PATCH v2 10/17] lkdtm: use __va_function

From: Nick Desaulniers <ndesaulniers@google.com>
To: Sami Tolvanen <samitolvanen@google.com>
Cc: Kees Cook <keescook@chromium.org>,
	Nathan Chancellor <nathan@kernel.org>,
	 Masahiro Yamada <masahiroy@kernel.org>,
	Will Deacon <will@kernel.org>, Jessica Yu <jeyu@kernel.org>,
	 Arnd Bergmann <arnd@arndb.de>, Tejun Heo <tj@kernel.org>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	 Christoph Hellwig <hch@infradead.org>, bpf <bpf@vger.kernel.org>,
	linux-hardening@vger.kernel.org,
	linux-arch <linux-arch@vger.kernel.org>,
	 Linux ARM <linux-arm-kernel@lists.infradead.org>,
	 Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
	PCI <linux-pci@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 10/17] lkdtm: use __va_function
Date: Thu, 18 Mar 2021 11:45:28 -0700	[thread overview]
Message-ID: <CAKwvOdk7wg-BoE=A0wN6Oz7ptK4y2_YHUBNTTc80CvWuY=nF3Q@mail.gmail.com> (raw)
In-Reply-To: <CAKwvOdkn7MY+-9D0DQ-18OR=s1XmgPaP7VchCm6VV5kYuKSAkA@mail.gmail.com>

On Thu, Mar 18, 2021 at 11:43 AM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> On Thu, Mar 18, 2021 at 10:11 AM Sami Tolvanen <samitolvanen@google.com> wrote:
> >
> > To ensure we take the actual address of a function in kernel text, use
> > __va_function. Otherwise, with CONFIG_CFI_CLANG, the compiler replaces
> > the address with a pointer to the CFI jump table, which is actually in
> > the module when compiled with CONFIG_LKDTM=m.
>
> Should patch 10 and 12 be reordered against one another? Otherwise it
> looks like 12 defines __va_function while 10 uses it?

Ah, nvm patch 3 defines a generic version, I see.

>
>
> >
> > Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> > Acked-by: Kees Cook <keescook@chromium.org>
> > ---
> >  drivers/misc/lkdtm/usercopy.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/misc/lkdtm/usercopy.c b/drivers/misc/lkdtm/usercopy.c
> > index 109e8d4302c1..d173d6175c87 100644
> > --- a/drivers/misc/lkdtm/usercopy.c
> > +++ b/drivers/misc/lkdtm/usercopy.c
> > @@ -314,7 +314,7 @@ void lkdtm_USERCOPY_KERNEL(void)
> >
> >         pr_info("attempting bad copy_to_user from kernel text: %px\n",
> >                 vm_mmap);
> > -       if (copy_to_user((void __user *)user_addr, vm_mmap,
> > +       if (copy_to_user((void __user *)user_addr, __va_function(vm_mmap),
> >                          unconst + PAGE_SIZE)) {
> >                 pr_warn("copy_to_user failed, but lacked Oops\n");
> >                 goto free_user;
> > --
> > 2.31.0.291.g576ba9dcdaf-goog
> >
>
>
> --
> Thanks,
> ~Nick Desaulniers

-- 
Thanks,
~Nick Desaulniers

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