Re: [PATCH] virt: acrn: Prefer array_syze and struct_size over open coded arithmetic

Len Baker
2021-10-15T15:53:11Z

Hi Li,

On Tue, Oct 12, 2021 at 09:34:29AM +0800, Li Fei1 wrote:
> On Mon, Oct 11, 2021 at 12:39:02PM +0200, Len Baker wrote:
> > 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@gmx.com>
>
> Hi Baker
>
> Thanks for helping us to fix this issue. This patch looks good to me.
> Please add Signed-off-by: Fei Li <fei1.li@intel.com>.

I can't add the "Signed-off-by" tag by myself. However, if you are in the
path to forward the patch to the mainline (maintainer's tree), you can
add by yourself the "Signed-off-by" tag before send a "pull" to Linus.
See [1] for more information.

[1] https://www.kernel.org/doc/html/latest/process/submitting-patches.html#sign-your-work-the-developer-s-certificate-of-origin

If you don't have a maintainer's tree, you can give (as a maintainer) an
"Acked-by" tag that then I can add to the patch. More info in [2].

[2] https://www.kernel.org/doc/html/latest/process/submitting-patches.html#when-to-use-acked-by-cc-and-co-developed-by

> Only two minor comments.
>
>
> > ---
> > 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.
> One Tab please.

Sorry, but if I use only one tab, the parameters description are not all
aligned.

> > *
> > * 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[];
> Please use Whitespace instead of Tab.

Sorry, but I don't understand. Do you prefer something like?:

diff --git a/drivers/virt/acrn/acrn_drv.h b/drivers/virt/acrn/acrn_drv.h
index fcc2e3e5232a..5663c17ad37c 100644
--- a/drivers/virt/acrn/acrn_drv.h
+++ b/drivers/virt/acrn/acrn_drv.h
@@ -56,11 +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;
- struct vm_memory_region_op regions_op[];
+ u16 vmid;
+ u16 reserved[3];
+ u32 regions_num;
+ u64 regions_gpa;
+ struct vm_memory_region_op regions_op[];
};

/**

Moreover, for the v2 I will fix the typo "syze->size" in the subject as
suggested Kees ;)

Regards,
Len