linux-hardening - Re: [PATCH 4/4] ptdump: add check_wx

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Date: Tue, 9 Jan 2024 14:50:05 +0100
From: Heiko Carstens <hca@...ux.ibm.com>
To: Christophe Leroy <christophe.leroy@...roup.eu>
Cc: linux-hardening@...r.kernel.org, Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...nel.org>,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org,
        linux-s390@...r.kernel.org, linux-mm@...ck.org, steven.price@....com,
        Phong Tran <tranmanphong@...il.com>, mark.rutland@....com,
        Greg KH <greg@...ah.com>
Subject: Re: [PATCH 4/4] ptdump: add check_wx_pages debugfs attribute

On Tue, Jan 09, 2024 at 01:14:38PM +0100, Christophe Leroy wrote:
> Add a writable attribute in debugfs to trigger a
> W^X pages check at any time.
> 
> To trigger the test, just echo any numeric value into
> /sys/kernel/debug/check_wx_pages
> 
> The result is provided into dmesg.
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> ---
>  mm/ptdump.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
...
> +static int check_wx_debugfs_set(void *data, u64 val)
> +{
> +	ptdump_check_wx();
> +
> +	return 0;
> +}
> +
> +DEFINE_SIMPLE_ATTRIBUTE(check_wx_fops, NULL, check_wx_debugfs_set, "%llu\n");
> +
> +static int ptdump_debugfs_init(void)
> +{
> +	debugfs_create_file("check_wx_pages", 0200, NULL, NULL, &check_wx_fops);
> +
> +	return 0;
> +}

Wouldn't it be better to have (only?) a readable attribute which triggers
this, and provides the result via this attribute?
That would allow for automated tests without having to parse dmesg.