linux-kernel - Re: [RFC PATCH v2] ptp: Add vDSO-style vmclock support

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Date: Sun, 30 Jun 2024 14:28:59 +0100
From: Simon Horman <horms@...nel.org>
To: David Woodhouse <dwmw2@...radead.org>
Cc: Peter Hilber <peter.hilber@...nsynergy.com>,
	linux-kernel@...r.kernel.org, virtualization@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org, linux-rtc@...r.kernel.org,
	"Ridoux, Julien" <ridouxj@...zon.com>, virtio-dev@...ts.linux.dev,
	"Luu, Ryan" <rluu@...zon.com>,
	"Christopher S. Hall" <christopher.s.hall@...el.com>,
	Jason Wang <jasowang@...hat.com>, John Stultz <jstultz@...gle.com>,
	"Michael S. Tsirkin" <mst@...hat.com>, netdev@...r.kernel.org,
	Richard Cochran <richardcochran@...il.com>,
	Stephen Boyd <sboyd@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	Marc Zyngier <maz@...nel.org>, Mark Rutland <mark.rutland@....com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Alessandro Zummo <a.zummo@...ertech.it>,
	Alexandre Belloni <alexandre.belloni@...tlin.com>,
	Kees Cook <kees@...nel.org>, linux-hardening@...r.kernel.org
Subject: Re: [RFC PATCH v2] ptp: Add vDSO-style vmclock support

+ Kees Cook, linux-hardening

On Tue, Jun 25, 2024 at 08:01:56PM +0100, David Woodhouse wrote:
> From: David Woodhouse <dwmw@...zon.co.uk>
> 
> The vmclock "device" provides a shared memory region with precision clock
> information. By using shared memory, it is safe across Live Migration.
> 
> Like the KVM PTP clock, this can convert TSC-based cross timestamps into
> KVM clock values. Unlike the KVM PTP clock, it does so only when such is
> actually helpful.
> 
> The memory region of the device is also exposed to userspace so it can be
> read or memory mapped by application which need reliable notification of
> clock disruptions.
> 
> Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>

...

> diff --git a/drivers/ptp/ptp_vmclock.c b/drivers/ptp/ptp_vmclock.c

...

> +static int vmclock_probe(struct platform_device *pdev)
> +{

...

> +	/* If there is valid clock information, register a PTP clock */
> +	if (st->cs_id) {
> +		st->ptp_clock_info = ptp_vmclock_info;
> +		strncpy(st->ptp_clock_info.name, st->name, sizeof(st->ptp_clock_info.name));

Hi David,

W=1 allmodconfig builds with gcc-13 flag the following.
Reading the documentation of strncpy() in fortify-string.h,
I wonder if strscpy() would be more appropriate in this case.

In file included from ./include/linux/string.h:374,
                 from ./include/linux/bitmap.h:13,
                 from ./include/linux/cpumask.h:13,
                 from ./arch/x86/include/asm/paravirt.h:21,
                 from ./arch/x86/include/asm/cpuid.h:62,
                 from ./arch/x86/include/asm/processor.h:19,
                 from ./include/linux/sched.h:13,
                 from ./include/linux/ratelimit.h:6,
                 from ./include/linux/dev_printk.h:16,
                 from ./include/linux/device.h:15,
                 from drivers/ptp/ptp_vmclock.c:8:
In function 'strncpy',
    inlined from 'vmclock_probe' at drivers/ptp/ptp_vmclock.c:480:3:
./include/linux/fortify-string.h:125:33: warning: '__builtin_strncpy' specified bound 32 equals destination size [-Wstringop-truncation]
  125 | #define __underlying_strncpy    __builtin_strncpy
      |                                 ^
./include/linux/fortify-string.h:205:16: note: in expansion of macro '__underlying_strncpy'
  205 |         return __underlying_strncpy(p, q, size);

...