linux-kernel - [PATCH v6 1/4] cacheinfo: Check for null last-level cache info

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Message-Id: <20240905060036.5655-2-ricardo.neri-calderon@linux.intel.com>
Date: Wed,  4 Sep 2024 23:00:33 -0700
From: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To: x86@...nel.org
Cc: Andreas Herrmann <aherrmann@...e.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Chen Yu <yu.c.chen@...el.com>,
	Len Brown <len.brown@...el.com>,
	Radu Rendec <rrendec@...hat.com>,
	Pierre Gondois <Pierre.Gondois@....com>,
	Pu Wen <puwen@...on.cn>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Sudeep Holla <sudeep.holla@....com>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Will Deacon <will@...nel.org>,
	Zhang Rui <rui.zhang@...el.com>,
	Nikolay Borisov <nik.borisov@...e.com>,
	Huang Ying <ying.huang@...el.com>,
	Ricardo Neri <ricardo.neri@...el.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH v6 1/4] cacheinfo: Check for null last-level cache info

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@...e.de>
Reviewed-by: Sudeep Holla <sudeep.holla@....com>
Tested-by: Andreas Herrmann <aherrmann@...e.de>
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
---
Cc: Andreas Herrmann <aherrmann@...e.com>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Chen Yu <yu.c.chen@...el.com>
Cc: Huang Ying <ying.huang@...el.com>
Cc: Len Brown <len.brown@...el.com>
Cc: Nikolay Borisov <nik.borisov@...e.com>
Cc: Radu Rendec <rrendec@...hat.com>
Cc: Pierre Gondois <Pierre.Gondois@....com>
Cc: Pu Wen <puwen@...on.cn>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Cc: Sudeep Holla <sudeep.holla@....com>
Cc: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Cc: Will Deacon <will@...nel.org>
Cc: Zhang Rui <rui.zhang@...el.com>
Cc: linux-arm-kernel@...ts.infradead.org
Cc: stable@...r.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