linux-kernel - Re: [kernel-hardening][PATCH v2 3/3] arm: mm: dump: add checking for writable and executable pages

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Date:   Sun, 3 Dec 2017 11:32:24 +0900
From:   park jinbum <jinb.park7@...il.com>
To:     Laura Abbott <labbott@...hat.com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        LKML <linux-kernel@...r.kernel.org>,
        kernel-hardening@...ts.openwall.com,
        Afzal Mohammed <afzal.mohd.ma@...il.com>,
        Mark Rutland <mark.rutland@....com>, linux@...linux.org.uk,
        gregkh@...uxfoundation.org, Kees Cook <keescook@...omium.org>,
        vladimir.murzin@....com, Arnd Bergmann <arnd@...db.de>
Subject: Re: [kernel-hardening][PATCH v2 3/3] arm: mm: dump: add checking for
 writable and executable pages

I agree with your opinion, Laura.
I'll make a new version to take advantage of the existing pg_level and
bits arrays.

Thanks,
Jinbum Park.

2017-12-02 6:59 GMT+09:00 Laura Abbott <labbott@...hat.com>:
> On 12/01/2017 03:34 AM, Jinbum Park wrote:
>>
>> +static inline bool is_prot_ro(struct pg_state *st)
>> +{
>> +       if (st->level < 4) {
>> +       #ifdef CONFIG_ARM_LPAE
>> +               if ((st->current_prot &
>> +               (L_PMD_SECT_RDONLY | PMD_SECT_AP2)) ==
>> +               (L_PMD_SECT_RDONLY | PMD_SECT_AP2))
>> +                       return true;
>> +       #elif __LINUX_ARM_ARCH__ >= 6
>> +               if ((st->current_prot &
>> +               (PMD_SECT_APX | PMD_SECT_AP_READ | PMD_SECT_AP_WRITE)) ==
>> +               (PMD_SECT_APX | PMD_SECT_AP_WRITE))
>> +                       return true;
>> +       #else
>> +               if ((st->current_prot &
>> +               (PMD_SECT_AP_READ | PMD_SECT_AP_WRITE)) == 0)
>> +                       return true;
>> +       #endif
>> +       } else {
>> +               if ((st->current_prot & L_PTE_RDONLY) == L_PTE_RDONLY)
>> +                       return true;
>> +       }
>> +
>> +       return false;
>> +}
>> +
>> +static inline bool is_prot_nx(struct pg_state *st)
>> +{
>> +       if (st->level < 4) {
>> +               if ((st->current_prot & PMD_SECT_XN) == PMD_SECT_XN)
>> +                       return true;
>> +       } else {
>> +               if ((st->current_prot & L_PTE_XN) == L_PTE_XN)
>> +                       return true;
>> +       }
>> +
>> +       return false;
>> +}
>
>
> I know arm64 checks the bits directly, but the arm32 code is a bit
> more fiddly and I have mixed feelings about copying and pasting
> the checks. It would be cleaner if we could take advantage of
> the existing pg_level and bits arrays. I also don't have my heart
> set on this so if nobody else objects, the code can stay as is.
>
> Thanks,
> Laura