linux-kernel - [PATCH] iommu/amd: Fix potential @entry null deref

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Message-Id: <20200910171621.12879-1-joao.m.martins@oracle.com>
Date:   Thu, 10 Sep 2020 18:16:21 +0100
From:   Joao Martins <joao.m.martins@...cle.com>
To:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Cc:     Dan Carpenter <dan.carpenter@...cle.com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        Joerg Roedel <joro@...tes.org>
Subject: [PATCH] iommu/amd: Fix potential @entry null deref

After commit 26e495f34107 ("iommu/amd: Restore IRTE.RemapEn bit after
programming IRTE"), smatch warns:

	drivers/iommu/amd/iommu.c:3870 amd_iommu_deactivate_guest_mode()
        warn: variable dereferenced before check 'entry' (see line 3867)

Fix this by moving the @valid assignment to after @entry has been checked
for NULL.

Cc: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Fixes: 26e495f34107 ("iommu/amd: Restore IRTE.RemapEn bit after programming IRTE")
Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
Signed-off-by: Joao Martins <joao.m.martins@...cle.com>
---
 drivers/iommu/amd/iommu.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
index 07ae8b93887e..8abe1c7ad45b 100644
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c
@@ -3864,12 +3864,14 @@ int amd_iommu_deactivate_guest_mode(void *data)
 	struct amd_ir_data *ir_data = (struct amd_ir_data *)data;
 	struct irte_ga *entry = (struct irte_ga *) ir_data->entry;
 	struct irq_cfg *cfg = ir_data->cfg;
-	u64 valid = entry->lo.fields_remap.valid;
+	u64 valid;
 
 	if (!AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir) ||
 	    !entry || !entry->lo.fields_vapic.guest_mode)
 		return 0;
 
+	valid = entry->lo.fields_remap.valid;
+
 	entry->lo.val = 0;
 	entry->hi.val = 0;
 
-- 
2.17.1