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Subject: Re: [PATCH] arm64: Clear the stack
To:     Kees Cook <keescook@chromium.org>
Cc:     Alexander Popov <alex.popov@linux.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Kernel Hardening <kernel-hardening@lists.openwall.com>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        LKML <linux-kernel@vger.kernel.org>
References: <20180629190553.7282-1-labbott@redhat.com>
 <CAGXu5jL8kZHtg-MdScZ5m_6xH_Ho4TsdKGWH83zEL9Y5rutncw@mail.gmail.com>
From:   Laura Abbott <labbott@redhat.com>
Message-ID: <706dc06b-0157-89cb-33a6-d0b9d811dcf0@redhat.com>
Date:   Fri, 29 Jun 2018 13:22:58 -0700
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On 06/29/2018 01:19 PM, Kees Cook wrote:
> On Fri, Jun 29, 2018 at 12:05 PM, Laura Abbott <labbott@redhat.com> wrote:
>> Implementation of stackleak based heavily on the x86 version
>>
>> Signed-off-by: Laura Abbott <labbott@redhat.com>
>> [...]
>> +#define current_top_of_stack() (task_stack_page(current) + THREAD_SIZE)
>> +#define on_thread_stack()      (on_task_stack(current, current_stack_pointer))
> 
> nit on types here. I get some warnings:
> 
> kernel/stackleak.c:55:12: warning: assignment makes integer from
> pointer without a cast [-Wint-conversion]
>     boundary = current_top_of_stack();
>              ^
> kernel/stackleak.c:65:24: warning: assignment makes integer from
> pointer without a cast [-Wint-conversion]
>    current->lowest_stack = current_top_of_stack() - THREAD_SIZE / 64;
>                          ^
> 
> So I think this needs to be:
> 
> +#define current_top_of_stack() ((unsigned long)task_stack_page(current) + \
> +                                THREAD_SIZE)
> 

Argh, missed that in an amend, can fix for next version if there
are no other objections to this approach.

>> diff --git a/scripts/Makefile.gcc-plugins b/scripts/Makefile.gcc-plugins
>> index a535742a1c06..972ce4ca7f6a 100644
>> --- a/scripts/Makefile.gcc-plugins
>> +++ b/scripts/Makefile.gcc-plugins
>> @@ -37,11 +37,14 @@ ifdef CONFIG_GCC_PLUGINS
>>
>>     gcc-plugin-$(CONFIG_GCC_PLUGIN_STACKLEAK)    += stackleak_plugin.so
>>     gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_STACKLEAK)     += -DSTACKLEAK_PLUGIN -fplugin-arg-stackleak_plugin-track-min-size=$(CONFIG_STACKLEAK_TRACK_MIN_SIZE)
>> +  ifdef CONFIG_GCC_PLUGIN_STACKLEAK
>> +    DISABLE_STACKLEAK_PLUGIN           += -fplugin-arg-stackleak_plugin-disable
>> +  endif
>>
>>     GCC_PLUGINS_CFLAGS := $(strip $(addprefix -fplugin=$(objtree)/scripts/gcc-plugins/, $(gcc-plugin-y)) $(gcc-plugin-cflags-y))
>>
>>     export PLUGINCC GCC_PLUGINS_CFLAGS GCC_PLUGIN GCC_PLUGIN_SUBDIR
>> -  export SANCOV_PLUGIN DISABLE_LATENT_ENTROPY_PLUGIN
>> +  export SANCOV_PLUGIN DISABLE_LATENT_ENTROPY_PLUGIN DISABLE_STACKLEAK_PLUGIN
>>
>>     ifneq ($(PLUGINCC),)
>>       # SANCOV_PLUGIN can be only in CFLAGS_KCOV because avoid duplication.
> 
> If there is a v14, I think this hunk should be taken there, since it's
> part of the common code.
> 
> Otherwise, this works for me and passes the lkdtm tests.
> 
> -Kees
> 

Thanks,
Laura