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Therefore dereferencing `limit` is > unsound. > > Fix this by changing the signature of `T::bios_limit` to return the limit > value. > `Registration::bios_limit_callback` can then update `limit` directly. > > Fixes: c6af9a1191d042839e56abff69e8b0302d117988 ("rust: cpufreq: Extend a= bstractions for driver registration") > Reported-by: Dylan Zueck > Reported-by: Yuan Tan > Signed-off-by: Priya Bala Govindasamy > Assisted-by: ChatGPT:gpt-5.4 You should move this line above your S-o-b. This tag should be covered by y= our S-o-b, not by whoever applies this patch. > > changes in v2: > - Change the signature of `T::bios_limit` and have > `Registration::bios_limit_callback` write to `limit` directly instead = of initializing `limit` to zero first and passing a mutable reference of `l= imit` to `T::bios_limit` > - v1 Link: https://lore.kernel.org/rust-for-linux/cover.1783456063.git.p= govind2@uci.edu/T/#t > --- > rust/kernel/cpufreq.rs | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 deletions(-) > > diff --git a/rust/kernel/cpufreq.rs b/rust/kernel/cpufreq.rs > index 58ac04c650a1..5dc09063f4e9 100644 > --- a/rust/kernel/cpufreq.rs > +++ b/rust/kernel/cpufreq.rs > @@ -817,7 +817,9 @@ fn update_limits(_policy: &mut Policy) { > } > =20 > /// Driver's `bios_limit` callback. > - fn bios_limit(_policy: &mut Policy, _limit: &mut u32) -> Result { > + /// > + /// Returns the limit The exisitng documentation is pointless. This really should just get proper documentation, e.g. /// Returns HW/BIOS max frequency limitations for the CPU. > + fn bios_limit(_policy: &mut Policy) -> Result { > build_error!(VTABLE_DEFAULT_ERROR) > } > =20 > @@ -1352,9 +1354,10 @@ impl Registration { > =20 > from_result(|| { > let mut policy =3D PolicyCpu::from_cpu(cpu_id)?; > - > + let val =3D T::bios_limit(&mut policy)?; > // SAFETY: `limit` is guaranteed by the C code to be valid. > - T::bios_limit(&mut policy, &mut (unsafe { *limit })).map(|()= | 0) > + unsafe { core::ptr::write(limit, val); } This is primitive so there's no dropping of old value, so this can just be unsafe { *limit =3D val; } Best, Gary > + Ok(0) > }) > } > =20