Before determining the validity of the last-level cache info, ensure that
it has been allocated. Simply checking for non-zero cache_leaves() is not
sufficient, as some architectures (e.g., Intel processors) have non-zero
cache_leaves() before allocation.

Dereferencing NULL cacheinfo can occur in update_per_cpu_data_slice_size().
This function iterates over all online CPUs. However, a CPU may have come
online recently, but its cacheinfo may not have been allocated yet.

Cc: Andreas Herrmann <aherrmann@suse.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Chen Yu <yu.c.chen@intel.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Len Brown <len.brown@intel.com>
Cc: Radu Rendec <rrendec@redhat.com>
Cc: Pierre Gondois <Pierre.Gondois@arm.com>
Cc: Pu Wen <puwen@hygon.cn>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Cc: Sudeep Holla <sudeep.holla@arm.com>
Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Cc: Will Deacon <will@kernel.org>
Cc: Zhang Rui <rui.zhang@intel.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: stable@vger.kernel.org
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
---
Changes since v3:
 * Introduced this patch.

Changes since v2:
 * N/A

Changes since v1:
 * N/A
---

The dereference of a NULL cacheinfo is not observed today because
cache_leaves(cpu) is zero until after init_cache_level() is called
(during the CPU hotplug callback). A subsequent changeset will set
the number of cache leaves earlier and the NULL-pointer dereference
will be observed.
---
 drivers/base/cacheinfo.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/base/cacheinfo.c b/drivers/base/cacheinfo.c
index f1e79263fe61..967c5cf3fb1d 100644
--- a/drivers/base/cacheinfo.c
+++ b/drivers/base/cacheinfo.c
@@ -61,6 +61,9 @@ bool last_level_cache_is_valid(unsigned int cpu)
 	if (!cache_leaves(cpu))
 		return false;
 
+	if (!per_cpu_cacheinfo(cpu))
+		return false;
+
 	llc = per_cpu_cacheinfo_idx(cpu, cache_leaves(cpu) - 1);
 
 	return (llc->attributes & CACHE_ID) || !!llc->fw_token;
-- 
2.25.1

On Tue, Dec 12, 2023 at 02:25:16PM -0800, Ricardo Neri wrote:
> Before determining the validity of the last-level cache info, ensure that
> it has been allocated. Simply checking for non-zero cache_leaves() is not
> sufficient, as some architectures (e.g., Intel processors) have non-zero
> cache_leaves() before allocation.
> 
> Dereferencing NULL cacheinfo can occur in update_per_cpu_data_slice_size().
> This function iterates over all online CPUs. However, a CPU may have come
> online recently, but its cacheinfo may not have been allocated yet.
> 
> Cc: Andreas Herrmann <aherrmann@suse.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Chen Yu <yu.c.chen@intel.com>
> Cc: Huang Ying <ying.huang@intel.com>
> Cc: Len Brown <len.brown@intel.com>
> Cc: Radu Rendec <rrendec@redhat.com>
> Cc: Pierre Gondois <Pierre.Gondois@arm.com>
> Cc: Pu Wen <puwen@hygon.cn>
> Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
> Cc: Sudeep Holla <sudeep.holla@arm.com>

If you respin, you can address the below minor nit. I am fine as is as
well.

Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>

[...]

> diff --git a/drivers/base/cacheinfo.c b/drivers/base/cacheinfo.c
> index f1e79263fe61..967c5cf3fb1d 100644
> --- a/drivers/base/cacheinfo.c
> +++ b/drivers/base/cacheinfo.c
> @@ -61,6 +61,9 @@ bool last_level_cache_is_valid(unsigned int cpu)
>  	if (!cache_leaves(cpu))
>  		return false;
>  
> +	if (!per_cpu_cacheinfo(cpu))
> +		return false;
> +

[nit] You can even combine this with above if condition.

-- 
Regards,
Sudeep

On Thu, Jan 25, 2024 at 11:15:44AM +0000, Sudeep Holla wrote:
> On Tue, Dec 12, 2023 at 02:25:16PM -0800, Ricardo Neri wrote:
> > Before determining the validity of the last-level cache info, ensure that
> > it has been allocated. Simply checking for non-zero cache_leaves() is not
> > sufficient, as some architectures (e.g., Intel processors) have non-zero
> > cache_leaves() before allocation.
> > 
> > Dereferencing NULL cacheinfo can occur in update_per_cpu_data_slice_size().
> > This function iterates over all online CPUs. However, a CPU may have come
> > online recently, but its cacheinfo may not have been allocated yet.
> > 
> > Cc: Andreas Herrmann <aherrmann@suse.com>
> > Cc: Catalin Marinas <catalin.marinas@arm.com>
> > Cc: Chen Yu <yu.c.chen@intel.com>
> > Cc: Huang Ying <ying.huang@intel.com>
> > Cc: Len Brown <len.brown@intel.com>
> > Cc: Radu Rendec <rrendec@redhat.com>
> > Cc: Pierre Gondois <Pierre.Gondois@arm.com>
> > Cc: Pu Wen <puwen@hygon.cn>
> > Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
> > Cc: Sudeep Holla <sudeep.holla@arm.com>
> 
> If you respin, you can address the below minor nit. I am fine as is as
> well.
> 
> Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>

Thank you for your review Sudeep!

> 
> [...]
> 
> > diff --git a/drivers/base/cacheinfo.c b/drivers/base/cacheinfo.c
> > index f1e79263fe61..967c5cf3fb1d 100644
> > --- a/drivers/base/cacheinfo.c
> > +++ b/drivers/base/cacheinfo.c
> > @@ -61,6 +61,9 @@ bool last_level_cache_is_valid(unsigned int cpu)
> >  	if (!cache_leaves(cpu))
> >  		return false;
> >  
> > +	if (!per_cpu_cacheinfo(cpu))
> > +		return false;
> > +
> 
> [nit] You can even combine this with above if condition.

Sure, I can take care of this if a new version is needed as per feedback
from the x86 maintainers.