Commit 3ad0876554ca ("xen/privcmd: add IOCTL_PRIVCMD_MMAP_RESOURCE")
introduced a static checker warning:
drivers/xen/privcmd.c:827 privcmd_ioctl_mmap_resource()
warn: passing casted pointer 'pfns' to 'xen_remap_domain_mfn_array()'
64 vs 32.
caused by this cast:
827 num = xen_remap_domain_mfn_array(vma,
828 kdata.addr & PAGE_MASK,
829 pfns, kdata.num, (int *)pfns,
^^^^^^^^^^^
The reason for the cast is that xen_remap_domain_mfn_array() requires an
array of ints to store error codes. It is actually safe to re-use the
pfns array for this purpose but it does look odd (as well as leading to
the warning). It would also be easy for a future implementation change
to make this re-use unsafe so this patch modifies privcmd to use a
separately allocated array for error codes.
Reported-by: Dan Carpenter <[email protected]>
Signed-off-by: Paul Durrant <[email protected]>
---
Cc: Boris Ostrovsky <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: Dan Carpenter <[email protected]>
---
drivers/xen/privcmd.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)
diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
index 8ae0349..8507c13 100644
--- a/drivers/xen/privcmd.c
+++ b/drivers/xen/privcmd.c
@@ -822,11 +822,18 @@ static long privcmd_ioctl_mmap_resource(struct file *file, void __user *udata)
unsigned int domid =
(xdata.flags & XENMEM_rsrc_acq_caller_owned) ?
DOMID_SELF : kdata.dom;
+ int *errs;
int num;
+ errs = kcalloc(kdata.num, sizeof(*errs), GFP_KERNEL);
+ if (!errs) {
+ rc = -ENOMEM;
+ goto out;
+ }
+
num = xen_remap_domain_mfn_array(vma,
kdata.addr & PAGE_MASK,
- pfns, kdata.num, (int *)pfns,
+ pfns, kdata.num, errs,
vma->vm_page_prot,
domid,
vma->vm_private_data);
@@ -836,12 +843,14 @@ static long privcmd_ioctl_mmap_resource(struct file *file, void __user *udata)
unsigned int i;
for (i = 0; i < num; i++) {
- rc = pfns[i];
+ rc = errs[i];
if (rc < 0)
break;
}
} else
rc = 0;
+
+ kfree(errs);
}
out:
--
2.1.4
On 07/06/18 11:21, Paul Durrant wrote:
> Commit 3ad0876554ca ("xen/privcmd: add IOCTL_PRIVCMD_MMAP_RESOURCE")
> introduced a static checker warning:
>
> drivers/xen/privcmd.c:827 privcmd_ioctl_mmap_resource()
> warn: passing casted pointer 'pfns' to 'xen_remap_domain_mfn_array()'
> 64 vs 32.
>
> caused by this cast:
>
> 827 num = xen_remap_domain_mfn_array(vma,
> 828 kdata.addr & PAGE_MASK,
> 829 pfns, kdata.num, (int *)pfns,
> ^^^^^^^^^^^
>
> The reason for the cast is that xen_remap_domain_mfn_array() requires an
> array of ints to store error codes. It is actually safe to re-use the
> pfns array for this purpose but it does look odd (as well as leading to
> the warning). It would also be easy for a future implementation change
> to make this re-use unsafe so this patch modifies privcmd to use a
> separately allocated array for error codes.
>
> Reported-by: Dan Carpenter <[email protected]>
> Signed-off-by: Paul Durrant <[email protected]>
It may be safe to reuse pfns[] as the storage space for the errs array,
but code is incorrect when sizeof(pfn) != sizeof(int). In such a case,
you skip over every other err, and second half of pfns[] is junk from
the point of view of the errs loop.
~Andrew
> ---
> Cc: Boris Ostrovsky <[email protected]>
> Cc: Juergen Gross <[email protected]>
> Cc: Dan Carpenter <[email protected]>
> ---
> drivers/xen/privcmd.c | 13 +++++++++++--
> 1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
> index 8ae0349..8507c13 100644
> --- a/drivers/xen/privcmd.c
> +++ b/drivers/xen/privcmd.c
> @@ -822,11 +822,18 @@ static long privcmd_ioctl_mmap_resource(struct file *file, void __user *udata)
> unsigned int domid =
> (xdata.flags & XENMEM_rsrc_acq_caller_owned) ?
> DOMID_SELF : kdata.dom;
> + int *errs;
> int num;
>
> + errs = kcalloc(kdata.num, sizeof(*errs), GFP_KERNEL);
> + if (!errs) {
> + rc = -ENOMEM;
> + goto out;
> + }
> +
> num = xen_remap_domain_mfn_array(vma,
> kdata.addr & PAGE_MASK,
> - pfns, kdata.num, (int *)pfns,
> + pfns, kdata.num, errs,
> vma->vm_page_prot,
> domid,
> vma->vm_private_data);
> @@ -836,12 +843,14 @@ static long privcmd_ioctl_mmap_resource(struct file *file, void __user *udata)
> unsigned int i;
>
> for (i = 0; i < num; i++) {
> - rc = pfns[i];
> + rc = errs[i];
> if (rc < 0)
> break;
> }
> } else
> rc = 0;
> +
> + kfree(errs);
> }
>
> out:
> -----Original Message-----
> From: Andrew Cooper
> Sent: 07 June 2018 11:28
> To: Paul Durrant <[email protected]>; [email protected];
> [email protected]
> Cc: Juergen Gross <[email protected]>; Boris Ostrovsky
> <[email protected]>; Dan Carpenter
> <[email protected]>
> Subject: Re: [Xen-devel] [PATCH] xen/privcmd: fix static checker warning
>
> On 07/06/18 11:21, Paul Durrant wrote:
> > Commit 3ad0876554ca ("xen/privcmd: add
> IOCTL_PRIVCMD_MMAP_RESOURCE")
> > introduced a static checker warning:
> >
> > drivers/xen/privcmd.c:827 privcmd_ioctl_mmap_resource()
> > warn: passing casted pointer 'pfns' to 'xen_remap_domain_mfn_array()'
> > 64 vs 32.
> >
> > caused by this cast:
> >
> > 827 num = xen_remap_domain_mfn_array(vma,
> > 828 kdata.addr & PAGE_MASK,
> > 829 pfns, kdata.num, (int *)pfns,
> > ^^^^^^^^^^^
> >
> > The reason for the cast is that xen_remap_domain_mfn_array() requires
> an
> > array of ints to store error codes. It is actually safe to re-use the
> > pfns array for this purpose but it does look odd (as well as leading to
> > the warning). It would also be easy for a future implementation change
> > to make this re-use unsafe so this patch modifies privcmd to use a
> > separately allocated array for error codes.
> >
> > Reported-by: Dan Carpenter <[email protected]>
> > Signed-off-by: Paul Durrant <[email protected]>
>
> It may be safe to reuse pfns[] as the storage space for the errs array,
> but code is incorrect when sizeof(pfn) != sizeof(int). In such a case,
> you skip over every other err, and second half of pfns[] is junk from
> the point of view of the errs loop.
>
Yep, that is indeed what happens without this patch.
Paul
> ~Andrew
>
> > ---
> > Cc: Boris Ostrovsky <[email protected]>
> > Cc: Juergen Gross <[email protected]>
> > Cc: Dan Carpenter <[email protected]>
> > ---
> > drivers/xen/privcmd.c | 13 +++++++++++--
> > 1 file changed, 11 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
> > index 8ae0349..8507c13 100644
> > --- a/drivers/xen/privcmd.c
> > +++ b/drivers/xen/privcmd.c
> > @@ -822,11 +822,18 @@ static long privcmd_ioctl_mmap_resource(struct
> file *file, void __user *udata)
> > unsigned int domid =
> > (xdata.flags & XENMEM_rsrc_acq_caller_owned) ?
> > DOMID_SELF : kdata.dom;
> > + int *errs;
> > int num;
> >
> > + errs = kcalloc(kdata.num, sizeof(*errs), GFP_KERNEL);
> > + if (!errs) {
> > + rc = -ENOMEM;
> > + goto out;
> > + }
> > +
> > num = xen_remap_domain_mfn_array(vma,
> > kdata.addr & PAGE_MASK,
> > - pfns, kdata.num, (int *)pfns,
> > + pfns, kdata.num, errs,
> > vma->vm_page_prot,
> > domid,
> > vma->vm_private_data);
> > @@ -836,12 +843,14 @@ static long privcmd_ioctl_mmap_resource(struct
> file *file, void __user *udata)
> > unsigned int i;
> >
> > for (i = 0; i < num; i++) {
> > - rc = pfns[i];
> > + rc = errs[i];
> > if (rc < 0)
> > break;
> > }
> > } else
> > rc = 0;
> > +
> > + kfree(errs);
> > }
> >
> > out:
On 07/06/18 13:23, Paul Durrant wrote:
>> -----Original Message-----
>> From: Andrew Cooper
>> Sent: 07 June 2018 11:28
>> To: Paul Durrant <[email protected]>; [email protected];
>> [email protected]
>> Cc: Juergen Gross <[email protected]>; Boris Ostrovsky
>> <[email protected]>; Dan Carpenter
>> <[email protected]>
>> Subject: Re: [Xen-devel] [PATCH] xen/privcmd: fix static checker warning
>>
>> On 07/06/18 11:21, Paul Durrant wrote:
>>> Commit 3ad0876554ca ("xen/privcmd: add
>> IOCTL_PRIVCMD_MMAP_RESOURCE")
>>> introduced a static checker warning:
>>>
>>> drivers/xen/privcmd.c:827 privcmd_ioctl_mmap_resource()
>>> warn: passing casted pointer 'pfns' to 'xen_remap_domain_mfn_array()'
>>> 64 vs 32.
>>>
>>> caused by this cast:
>>>
>>> 827 num = xen_remap_domain_mfn_array(vma,
>>> 828 kdata.addr & PAGE_MASK,
>>> 829 pfns, kdata.num, (int *)pfns,
>>> ^^^^^^^^^^^
>>>
>>> The reason for the cast is that xen_remap_domain_mfn_array() requires
>> an
>>> array of ints to store error codes. It is actually safe to re-use the
>>> pfns array for this purpose but it does look odd (as well as leading to
>>> the warning). It would also be easy for a future implementation change
>>> to make this re-use unsafe so this patch modifies privcmd to use a
>>> separately allocated array for error codes.
>>>
>>> Reported-by: Dan Carpenter <[email protected]>
>>> Signed-off-by: Paul Durrant <[email protected]>
>>
>> It may be safe to reuse pfns[] as the storage space for the errs array,
>> but code is incorrect when sizeof(pfn) != sizeof(int). In such a case,
>> you skip over every other err, and second half of pfns[] is junk from
>> the point of view of the errs loop.
>>
>
> Yep, that is indeed what happens without this patch.
Can you please update the commit message accordingly?
Juergen