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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Thu, 18 Mar 2021 11:43:29 -0700
Message-ID: <CAKwvOdkn7MY+-9D0DQ-18OR=s1XmgPaP7VchCm6VV5kYuKSAkA@mail.gmail.com>
Subject: Re: [PATCH v2 10/17] lkdtm: use __va_function
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>
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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?


>
> 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