linux-kernel - [PATCH] swiotlb: Initialise restricted pool list_head when SWIOTLB

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Message-Id: <20240502093723.16820-1-will@kernel.org>
Date: Thu,  2 May 2024 10:37:23 +0100
From: Will Deacon <will@...nel.org>
To: linux-kernel@...r.kernel.org
Cc: iommu@...ts.linux.dev,
	Will Deacon <will@...nel.org>,
	Christoph Hellwig <hch@....de>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Robin Murphy <robin.murphy@....com>,
	Petr Tesařík <petr@...arici.cz>,
	Michael Kelley <mhkelley58@...il.com>,
	Nikita Ioffe <ioffe@...gle.com>
Subject: [PATCH] swiotlb: Initialise restricted pool list_head when SWIOTLB_DYNAMIC=y

Using restricted DMA pools (CONFIG_DMA_RESTRICTED_POOL=y) in conjunction
with dynamic SWIOTLB (CONFIG_SWIOTLB_DYNAMIC=y) leads to the following
crash when initialising the restricted pools at boot-time:

  | Unable to handle kernel NULL pointer dereference at virtual address 0000000000000008
  | Internal error: Oops: 0000000096000005 [#1] PREEMPT SMP
  | pc : rmem_swiotlb_device_init+0xfc/0x1ec
  | lr : rmem_swiotlb_device_init+0xf0/0x1ec
  | Call trace:
  |  rmem_swiotlb_device_init+0xfc/0x1ec
  |  of_reserved_mem_device_init_by_idx+0x18c/0x238
  |  of_dma_configure_id+0x31c/0x33c
  |  platform_dma_configure+0x34/0x80

faddr2line reveals that the crash is in the list validation code:

  include/linux/list.h:83
  include/linux/rculist.h:79
  include/linux/rculist.h:106
  kernel/dma/swiotlb.c:306
  kernel/dma/swiotlb.c:1695

because add_mem_pool() is trying to list_add_rcu() to a NULL
'mem->pools'.

Fix the crash by initialising the 'mem->pools' list_head in
rmem_swiotlb_device_init() before calling add_mem_pool().

Cc: Christoph Hellwig <hch@....de>
Cc: Marek Szyprowski <m.szyprowski@...sung.com>
Cc: Robin Murphy <robin.murphy@....com>
Cc: Petr Tesařík <petr@...arici.cz>
Cc: Michael Kelley <mhkelley58@...il.com>
Reported-by: Nikita Ioffe <ioffe@...gle.com>
Tested-by: Nikita Ioffe <ioffe@...gle.com>
Fixes: 1aaa736815eb ("swiotlb: allocate a new memory pool when existing pools are full")
Signed-off-by: Will Deacon <will@...nel.org>
---
 kernel/dma/swiotlb.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 86fe172b5958..87dd3301dde3 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -1773,6 +1773,7 @@ static int rmem_swiotlb_device_init(struct reserved_mem *rmem,
 		mem->for_alloc = true;
 #ifdef CONFIG_SWIOTLB_DYNAMIC
 		spin_lock_init(&mem->lock);
+		INIT_LIST_HEAD_RCU(&mem->pools);
 #endif
 		add_mem_pool(mem, pool);
 
-- 
2.45.0.rc1.225.g2a3ae87e7f-goog