linux-kernel - [PATCH] timekeeping: Always initialize use_nsecs when querying time from phc drivers

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Message-ID: <txyrr26hxe3xpq3ebqb5ewkgvhvp7xalotaouwludjtjifnah2@7tmgczln4aoo>
Date: Tue, 8 Jul 2025 18:46:01 +0200
From: Markus Blöchl <markus.bloechl@...tronik.com>
To: Thomas Gleixner <tglx@...utronix.de>, 
	"Christopher S. Hall" <christopher.s.hall@...el.com>, Lakshmi Sowjanya D <lakshmi.sowjanya.d@...el.com>
Cc: John Stultz <jstultz@...gle.com>, Stephen Boyd <sboyd@...nel.org>, 
	linux-kernel@...r.kernel.org
Subject: [PATCH] timekeeping: Always initialize use_nsecs when querying time
 from phc drivers

Most drivers only populate the fields cycles and cs_id in their
get_time_fn() callback for get_device_system_crosststamp() unless
they explicitly provide nanosecond values.
When this new use_nsecs field was added and used most drivers did not
care.
Clock sources other than CSID_GENERIC could then get converted in
convert_base_to_cs() based on an uninitialized use_nsecs which usually
results in -EINVAL during the following range check.

Fixes: 6b2e29977518 ("timekeeping: Provide infrastructure for converting to/from a base clock")
Cc: stable@...r.kernel.org
Signed-off-by: Markus Blöchl <markus.bloechl@...tronik.com>
---

Notes:
    We observed this in the e1000e driver but at least stmmac and
    ptp_kvm also seem affected by this.
    ice was recently fixed by a5a441ae283d ("ice/ptp: fix crosstimestamp reporting").


 kernel/time/timekeeping.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index a009c91f7b05..be0da807329f 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1269,6 +1269,8 @@ int get_device_system_crosststamp(int (*get_time_fn)

        do {
                seq = read_seqcount_begin(&tk_core.seq);
+               system_counterval.use_nsecs = false;
+
                /*
                 * Try to synchronously capture device time and a system
                 * counter value calling back into the device driver

base-commit: d7b8f8e20813f0179d8ef519541a3527e7661d3a
--
2.50.0


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