linux-kernel - [PATCH 1/4] iommu/amd: Do proper access checking before calling handle_mm

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Date:	Tue, 17 Nov 2015 16:11:36 +0100
From:	Joerg Roedel <joro@...tes.org>
To:	iommu@...ts.linux-foundation.org
Cc:	Oded Gabbay <oded.gabbay@...il.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Joerg Roedel <jroedel@...e.de>
Subject: [PATCH 1/4] iommu/amd: Do proper access checking before calling handle_mm_fault()

From: Joerg Roedel <jroedel@...e.de>

The handle_mm_fault function expects the caller to do the
access checks. Not doing so and calling the function with
wrong permissions is a bug (catched by a BUG_ON).
So fix this bug by adding proper access checking to the io
page-fault code in the AMD IOMMUv2 driver.

Signed-off-by: Joerg Roedel <jroedel@...e.de>
---
 drivers/iommu/amd_iommu_v2.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/amd_iommu_v2.c b/drivers/iommu/amd_iommu_v2.c
index d21d4ed..7caf2fa 100644
--- a/drivers/iommu/amd_iommu_v2.c
+++ b/drivers/iommu/amd_iommu_v2.c
@@ -494,6 +494,22 @@ static void handle_fault_error(struct fault *fault)
 	}
 }
 
+static bool access_error(struct vm_area_struct *vma, struct fault *fault)
+{
+	unsigned long requested = 0;
+
+	if (fault->flags & PPR_FAULT_EXEC)
+		requested |= VM_EXEC;
+
+	if (fault->flags & PPR_FAULT_READ)
+		requested |= VM_READ;
+
+	if (fault->flags & PPR_FAULT_WRITE)
+		requested |= VM_WRITE;
+
+	return (requested & ~vma->vm_flags) != 0;
+}
+
 static void do_fault(struct work_struct *work)
 {
 	struct fault *fault = container_of(work, struct fault, work);
@@ -516,8 +532,8 @@ static void do_fault(struct work_struct *work)
 		goto out;
 	}
 
-	if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE))) {
-		/* handle_mm_fault would BUG_ON() */
+	/* Check if we have the right permissions on the vma */
+	if (access_error(vma, fault)) {
 		up_read(&mm->mmap_sem);
 		handle_fault_error(fault);
 		goto out;
-- 
1.9.1

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