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.

Reviewed-by: Andreas Herrmann <aherrmann@suse.de>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
Tested-by: Andreas Herrmann <aherrmann@suse.de>
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
---
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: Nikolay Borisov <nik.borisov@suse.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 # 6.3+
---
Changes since v5:
 * Added Reviewed-by and Tested-by tags from Andreas. Thanks!

Changes since v4:
 * Combined checks for per_cpu_cacheinfo() and cache_leaves() in a single
   line. (Sudeep)
 * Added Reviewed-by tag from Sudeep. Thanks!

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 | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/base/cacheinfo.c b/drivers/base/cacheinfo.c
index 23b8cba4a2a3..77f2e0f91589 100644
--- a/drivers/base/cacheinfo.c
+++ b/drivers/base/cacheinfo.c
@@ -58,7 +58,7 @@ bool last_level_cache_is_valid(unsigned int cpu)
 {
 	struct cacheinfo *llc;
 
-	if (!cache_leaves(cpu))
+	if (!cache_leaves(cpu) || !per_cpu_cacheinfo(cpu))
 		return false;
 
 	llc = per_cpu_cacheinfo_idx(cpu, cache_leaves(cpu) - 1);
-- 
2.34.1

On Wed, Sep 04, 2024 at 11:00:33PM -0700, 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.
> 
> Reviewed-by: Andreas Herrmann <aherrmann@suse.de>
> Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
> Tested-by: Andreas Herrmann <aherrmann@suse.de>
> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>

While at it, pls fix the formatting insanity of allocate_cache_info() into:

static inline int allocate_cache_info(int cpu)
{
        per_cpu_cacheinfo(cpu) = kcalloc(cache_leaves(cpu), sizeof(struct cacheinfo), GFP_ATOMIC);
        if (!per_cpu_cacheinfo(cpu)) {
                cache_leaves(cpu) = 0;
                return -ENOMEM;
        }
            
        return 0;
}

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

On Wed, Sep 11, 2024 at 04:05:09PM +0200, Borislav Petkov wrote:
> On Wed, Sep 04, 2024 at 11:00:33PM -0700, 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.
> > 
> > Reviewed-by: Andreas Herrmann <aherrmann@suse.de>
> > Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
> > Tested-by: Andreas Herrmann <aherrmann@suse.de>
> > Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
> 
> While at it, pls fix the formatting insanity of allocate_cache_info() into:
> 
> static inline int allocate_cache_info(int cpu)
> {
>         per_cpu_cacheinfo(cpu) = kcalloc(cache_leaves(cpu), sizeof(struct cacheinfo), GFP_ATOMIC);
>         if (!per_cpu_cacheinfo(cpu)) {
>                 cache_leaves(cpu) = 0;
>                 return -ENOMEM;
>         }
>             
>         return 0;
> }
> 
> Thx.

Sure! I can do this. I assume this should be a separate patch.

On Wed, Sep 11, 2024 at 04:37:46PM -0700, Ricardo Neri wrote:
> Sure! I can do this. I assume this should be a separate patch.

Not needed.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette