linux-kernel - [PATCH v2 09/14] mm: Pcpu chunk address tag reset

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Message-ID: <383482f87ad4f68690021e0cc75df8143b6babe2.1739866028.git.maciej.wieczor-retman@intel.com>
Date: Tue, 18 Feb 2025 09:15:25 +0100
From: Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>
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Subject: [PATCH v2 09/14] mm: Pcpu chunk address tag reset

The problem presented here is related to NUMA systems and tag-based
KASAN mode. Getting to it can be explained in the following points:

	1. A new chunk is created with pcpu_create_chunk() and
	   vm_structs are allocated. On systems with one NUMA node only
	   one is allocated, but with more NUMA nodes at least a second
	   one will be allocated too.

	2. chunk->base_addr is assigned the modified value of
	   vms[0]->addr and thus inherits the tag of this allocated
	   structure.

	3. In pcpu_alloc() for each possible cpu pcpu_chunk_addr() is
	   executed which calculates per cpu pointers that correspond to
	   the vms structure addresses. The calculations are based on
	   adding an offset from a table to chunk->base_addr.

Here the problem presents itself since for addresses based on vms[1] and
up, the tag will be different than the ones based on vms[0] (base_addr).
The tag mismatch happens and an error is reported.

Reset the base_addr tag, since it will disable tag checks for pointers
derived arithmetically from base_addr that would inherit its tag.

Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>
---
 mm/percpu-vm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/percpu-vm.c b/mm/percpu-vm.c
index cd69caf6aa8d..e13750d804f7 100644
--- a/mm/percpu-vm.c
+++ b/mm/percpu-vm.c
@@ -347,7 +347,7 @@ static struct pcpu_chunk *pcpu_create_chunk(gfp_t gfp)
 	}
 
 	chunk->data = vms;
-	chunk->base_addr = vms[0]->addr - pcpu_group_offsets[0];
+	chunk->base_addr = kasan_reset_tag(vms[0]->addr) - pcpu_group_offsets[0];
 
 	pcpu_stats_chunk_alloc();
 	trace_percpu_create_chunk(chunk->base_addr);
-- 
2.47.1