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

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Message-ID: <23def981-3f61-8421-b46d-94f75b293003@redhat.com>
Date:   Fri, 1 Dec 2017 13:59:48 -0800
From:   Laura Abbott <labbott@...hat.com>
To:     Jinbum Park <jinb.park7@...il.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kernel-hardening@...ts.openwall.com
Cc:     afzal.mohd.ma@...il.com, mark.rutland@....com,
        linux@...linux.org.uk, gregkh@...uxfoundation.org,
        keescook@...omium.org, vladimir.murzin@....com, arnd@...db.de
Subject: Re: [kernel-hardening][PATCH v2 3/3] arm: mm: dump: add checking for
 writable and executable pages

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