linux-kernel - [PATCH] iommu: Use correctly sized arguments for bit field

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Date:   Wed, 15 Dec 2021 15:24:32 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Kees Cook <keescook@...omium.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Yury Norov <yury.norov@...il.com>,
        linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        linux-hardening@...r.kernel.org
Subject: [PATCH] iommu: Use correctly sized arguments for bit field

The find.h APIs are designed to be used only on unsigned long arguments.
This can technically result in a over-read, but it is harmless in this
case. Regardless, fix it to avoid the warning seen under -Warray-bounds,
which we'd like to enable globally:

In file included from ./include/linux/bitmap.h:9,
                 from drivers/iommu/intel/iommu.c:17:
drivers/iommu/intel/iommu.c: In function 'domain_context_mapping_one':
./include/linux/find.h:119:37: warning: array subscript 'long unsigned int[0]' is partly outside array bounds of 'int[1]' [-Warray-bounds]
  119 |                 unsigned long val = *addr & GENMASK(size - 1, 0);
      |                                     ^~~~~
drivers/iommu/intel/iommu.c:2115:18: note: while referencing 'max_pde'
 2115 |         int pds, max_pde;
      |                  ^~~~~~~

Signed-off-by: Kees Cook <keescook@...omium.org>
---
 drivers/iommu/intel/iommu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index b6a8f3282411..99f9e8229384 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -2112,10 +2112,10 @@ static void domain_exit(struct dmar_domain *domain)
  */
 static inline unsigned long context_get_sm_pds(struct pasid_table *table)
 {
-	int pds, max_pde;
+	unsigned long pds, max_pde;
 
 	max_pde = table->max_pasid >> PASID_PDE_SHIFT;
-	pds = find_first_bit((unsigned long *)&max_pde, MAX_NR_PASID_BITS);
+	pds = find_first_bit(&max_pde, MAX_NR_PASID_BITS);
 	if (pds < 7)
 		return 0;
 
-- 
2.30.2