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

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Date:   Fri, 15 Oct 2021 17:52:48 +0200
From:   Len Baker <len.baker@....com>
To:     Li Fei1 <fei1.li@...el.com>
Cc:     Len Baker <len.baker@....com>, keescook@...omium.org,
        gustavoars@...nel.org, linux-hardening@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] virt: acrn: Prefer array_syze and struct_size over open
 coded arithmetic

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@....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@...el.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