linux-hardening - [PATCH] virt: acrn: Prefer array_syze and struct

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Date:   Mon, 11 Oct 2021 12:39:02 +0200
From:   Len Baker <len.baker@....com>
To:     Fei Li <fei1.li@...el.com>
Cc:     Len Baker <len.baker@....com>, Kees Cook <keescook@...omium.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] virt: acrn: Prefer array_syze and struct_size over open coded arithmetic

As noted in the "Deprecated Interfaces, Language Features, Attributes,
and Conventions" documentation [1], size calculations (especially
multiplication) should not be performed in memory allocator (or similar)
function arguments due to the risk of them overflowing. This could lead
to values wrapping around and a smaller allocation being made than the
caller was expecting. Using those allocations could lead to linear
overflows of heap memory and other misbehaviors.

So, use the array_size() helper to do the arithmetic instead of the
argument "count * size" in the vzalloc() function.

Also, take the opportunity to add a flexible array member of struct
vm_memory_region_op to the vm_memory_region_batch structure. And then,
change the code accordingly and use the struct_size() helper to do the
arithmetic instead of the argument "size + size * count" in the kzalloc
function.

This code was detected with the help of Coccinelle and audited and fixed
manually.

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments

Signed-off-by: Len Baker <len.baker@....com>
---
 drivers/virt/acrn/acrn_drv.h | 10 ++++++----
 drivers/virt/acrn/mm.c       |  9 ++++-----
 2 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/drivers/virt/acrn/acrn_drv.h b/drivers/virt/acrn/acrn_drv.h
index 1be54efa666c..fcc2e3e5232a 100644
--- a/drivers/virt/acrn/acrn_drv.h
+++ b/drivers/virt/acrn/acrn_drv.h
@@ -48,6 +48,7 @@ struct vm_memory_region_op {
  * @reserved:		Reserved.
  * @regions_num:	The number of vm_memory_region_op.
  * @regions_gpa:	Physical address of a vm_memory_region_op array.
+ * @regions_op:		Flexible array of vm_memory_region_op.
  *
  * HC_VM_SET_MEMORY_REGIONS uses this structure to manage EPT mappings of
  * multiple memory regions of a User VM. A &struct vm_memory_region_batch
@@ -55,10 +56,11 @@ struct vm_memory_region_op {
  * ACRN Hypervisor.
  */
 struct vm_memory_region_batch {
-	u16	vmid;
-	u16	reserved[3];
-	u32	regions_num;
-	u64	regions_gpa;
+	u16				vmid;
+	u16				reserved[3];
+	u32				regions_num;
+	u64				regions_gpa;
+	struct vm_memory_region_op	regions_op[];
 };

 /**
diff --git a/drivers/virt/acrn/mm.c b/drivers/virt/acrn/mm.c
index c4f2e15c8a2b..a881742cd48d 100644
--- a/drivers/virt/acrn/mm.c
+++ b/drivers/virt/acrn/mm.c
@@ -168,7 +168,7 @@ int acrn_vm_ram_map(struct acrn_vm *vm, struct acrn_vm_memmap *memmap)

 	/* Get the page number of the map region */
 	nr_pages = memmap->len >> PAGE_SHIFT;
-	pages = vzalloc(nr_pages * sizeof(struct page *));
+	pages = vzalloc(array_size(nr_pages, sizeof(struct page *)));
 	if (!pages)
 		return -ENOMEM;

@@ -220,16 +220,15 @@ int acrn_vm_ram_map(struct acrn_vm *vm, struct acrn_vm_memmap *memmap)
 	}

 	/* Prepare the vm_memory_region_batch */
-	regions_info = kzalloc(sizeof(*regions_info) +
-			       sizeof(*vm_region) * nr_regions,
-			       GFP_KERNEL);
+	regions_info = kzalloc(struct_size(regions_info, regions_op,
+					   nr_regions), GFP_KERNEL);
 	if (!regions_info) {
 		ret = -ENOMEM;
 		goto unmap_kernel_map;
 	}

 	/* Fill each vm_memory_region_op */
-	vm_region = (struct vm_memory_region_op *)(regions_info + 1);
+	vm_region = regions_info->regions_op;
 	regions_info->vmid = vm->vmid;
 	regions_info->regions_num = nr_regions;
 	regions_info->regions_gpa = virt_to_phys(vm_region);
--
2.25.1