linux-hardening - Re: [PATCH v2 10/17] lkdtm: use __va

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Date:   Thu, 18 Mar 2021 11:45:28 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Will Deacon <will@...nel.org>, Jessica Yu <jeyu@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, Tejun Heo <tj@...nel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Christoph Hellwig <hch@...radead.org>,
        bpf <bpf@...r.kernel.org>, linux-hardening@...r.kernel.org,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        PCI <linux-pci@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 10/17] lkdtm: use __va_function

On Thu, Mar 18, 2021 at 11:43 AM Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
>
> On Thu, Mar 18, 2021 at 10:11 AM Sami Tolvanen <samitolvanen@...gle.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@...gle.com>
> > Acked-by: Kees Cook <keescook@...omium.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