[PATCH][next] xen: privcmd: Replace zero-length array with flex-array member and use __counted_by

[PATCH][next] xen: privcmd: Replace zero-length array with flex-array member and use __counted_by

[Gustavo A. R. Silva]

Fake flexible arrays (zero-length and one-element arrays) are deprecated,
and should be replaced by flexible-array members. So, replace
zero-length array with a flexible-array member in `struct
privcmd_kernel_ioreq`.

Also annotate array `ports` with `__counted_by()` to prepare for the
coming implementation by GCC and Clang of the `__counted_by` attribute.
Flexible array members annotated with `__counted_by` can have their
accesses bounds-checked at run-time via `CONFIG_UBSAN_BOUNDS` (for array
indexing) and `CONFIG_FORTIFY_SOURCE` (for strcpy/memcpy-family functions).

This fixes multiple -Warray-bounds warnings:
drivers/xen/privcmd.c:1239:30: warning: array subscript i is outside array bounds of 'struct ioreq_port[0]' [-Warray-bounds=]
drivers/xen/privcmd.c:1240:30: warning: array subscript i is outside array bounds of 'struct ioreq_port[0]' [-Warray-bounds=]
drivers/xen/privcmd.c:1241:30: warning: array subscript i is outside array bounds of 'struct ioreq_port[0]' [-Warray-bounds=]
drivers/xen/privcmd.c:1245:33: warning: array subscript i is outside array bounds of 'struct ioreq_port[0]' [-Warray-bounds=]
drivers/xen/privcmd.c:1258:67: warning: array subscript i is outside array bounds of 'struct ioreq_port[0]' [-Warray-bounds=]

This results in no differences in binary output.

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 drivers/xen/privcmd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
index 1ce7f3c7a950..0eb337a8ec0f 100644
--- a/drivers/xen/privcmd.c
+++ b/drivers/xen/privcmd.c
@@ -1115,7 +1115,7 @@ struct privcmd_kernel_ioreq {
 	spinlock_t lock; /* Protects ioeventfds list */
 	struct list_head ioeventfds;
 	struct list_head list;
-	struct ioreq_port ports[0];
+	struct ioreq_port ports[] __counted_by(vcpus);
 };
 
 static irqreturn_t ioeventfd_interrupt(int irq, void *dev_id)
-- 
2.34.1

Re: [PATCH][next] xen: privcmd: Replace zero-length array with flex-array member and use __counted_by

[Kees Cook]

On Thu, Nov 16, 2023 at 12:54:59PM -0600, Gustavo A. R. Silva wrote:
> Fake flexible arrays (zero-length and one-element arrays) are deprecated,
> and should be replaced by flexible-array members. So, replace
> zero-length array with a flexible-array member in `struct
> privcmd_kernel_ioreq`.
> 
> Also annotate array `ports` with `__counted_by()` to prepare for the
> coming implementation by GCC and Clang of the `__counted_by` attribute.
> Flexible array members annotated with `__counted_by` can have their
> accesses bounds-checked at run-time via `CONFIG_UBSAN_BOUNDS` (for array
> indexing) and `CONFIG_FORTIFY_SOURCE` (for strcpy/memcpy-family functions).
> 
> This fixes multiple -Warray-bounds warnings:
> drivers/xen/privcmd.c:1239:30: warning: array subscript i is outside array bounds of 'struct ioreq_port[0]' [-Warray-bounds=]
> drivers/xen/privcmd.c:1240:30: warning: array subscript i is outside array bounds of 'struct ioreq_port[0]' [-Warray-bounds=]
> drivers/xen/privcmd.c:1241:30: warning: array subscript i is outside array bounds of 'struct ioreq_port[0]' [-Warray-bounds=]
> drivers/xen/privcmd.c:1245:33: warning: array subscript i is outside array bounds of 'struct ioreq_port[0]' [-Warray-bounds=]
> drivers/xen/privcmd.c:1258:67: warning: array subscript i is outside array bounds of 'struct ioreq_port[0]' [-Warray-bounds=]
> 
> This results in no differences in binary output.
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Looks right to me. I can see the allocation:

        size = struct_size(kioreq, ports, ioeventfd->vcpus);
        kioreq = kzalloc(size, GFP_KERNEL);
        if (!kioreq)
                return ERR_PTR(-ENOMEM);

        kioreq->dom = ioeventfd->dom;
        kioreq->vcpus = ioeventfd->vcpus;


Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook

Re: [PATCH][next] xen: privcmd: Replace zero-length array with flex-array member and use __counted_by

[Gustavo A. R. Silva]

On 11/16/23 15:08, Kees Cook wrote:
> On Thu, Nov 16, 2023 at 12:54:59PM -0600, Gustavo A. R. Silva wrote:
>> Fake flexible arrays (zero-length and one-element arrays) are deprecated,
>> and should be replaced by flexible-array members. So, replace
>> zero-length array with a flexible-array member in `struct
>> privcmd_kernel_ioreq`.
>>
>> Also annotate array `ports` with `__counted_by()` to prepare for the
>> coming implementation by GCC and Clang of the `__counted_by` attribute.
>> Flexible array members annotated with `__counted_by` can have their
>> accesses bounds-checked at run-time via `CONFIG_UBSAN_BOUNDS` (for array
>> indexing) and `CONFIG_FORTIFY_SOURCE` (for strcpy/memcpy-family functions).
>>
>> This fixes multiple -Warray-bounds warnings:
>> drivers/xen/privcmd.c:1239:30: warning: array subscript i is outside array bounds of 'struct ioreq_port[0]' [-Warray-bounds=]
>> drivers/xen/privcmd.c:1240:30: warning: array subscript i is outside array bounds of 'struct ioreq_port[0]' [-Warray-bounds=]
>> drivers/xen/privcmd.c:1241:30: warning: array subscript i is outside array bounds of 'struct ioreq_port[0]' [-Warray-bounds=]
>> drivers/xen/privcmd.c:1245:33: warning: array subscript i is outside array bounds of 'struct ioreq_port[0]' [-Warray-bounds=]
>> drivers/xen/privcmd.c:1258:67: warning: array subscript i is outside array bounds of 'struct ioreq_port[0]' [-Warray-bounds=]
>>
>> This results in no differences in binary output.
>>
>> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> 
> Looks right to me. I can see the allocation:

Yep, I always check for that; in particular, the 'counter' assignment. :)

Do you want me to mention it in the changelog text?

> 
>          size = struct_size(kioreq, ports, ioeventfd->vcpus);
>          kioreq = kzalloc(size, GFP_KERNEL);
>          if (!kioreq)
>                  return ERR_PTR(-ENOMEM);
> 
>          kioreq->dom = ioeventfd->dom;
>          kioreq->vcpus = ioeventfd->vcpus;
> 
> 
> Reviewed-by: Kees Cook <keescook@chromium.org>

Thanks!
--
Gustavo

Re: [PATCH][next] xen: privcmd: Replace zero-length array with flex-array member and use __counted_by

[Juergen Gross]

[-- Attachment #1.1.1: Type: text/plain, Size: 1535 bytes --]

On 16.11.23 19:54, Gustavo A. R. Silva wrote:
> Fake flexible arrays (zero-length and one-element arrays) are deprecated,
> and should be replaced by flexible-array members. So, replace
> zero-length array with a flexible-array member in `struct
> privcmd_kernel_ioreq`.
> 
> Also annotate array `ports` with `__counted_by()` to prepare for the
> coming implementation by GCC and Clang of the `__counted_by` attribute.
> Flexible array members annotated with `__counted_by` can have their
> accesses bounds-checked at run-time via `CONFIG_UBSAN_BOUNDS` (for array
> indexing) and `CONFIG_FORTIFY_SOURCE` (for strcpy/memcpy-family functions).
> 
> This fixes multiple -Warray-bounds warnings:
> drivers/xen/privcmd.c:1239:30: warning: array subscript i is outside array bounds of 'struct ioreq_port[0]' [-Warray-bounds=]
> drivers/xen/privcmd.c:1240:30: warning: array subscript i is outside array bounds of 'struct ioreq_port[0]' [-Warray-bounds=]
> drivers/xen/privcmd.c:1241:30: warning: array subscript i is outside array bounds of 'struct ioreq_port[0]' [-Warray-bounds=]
> drivers/xen/privcmd.c:1245:33: warning: array subscript i is outside array bounds of 'struct ioreq_port[0]' [-Warray-bounds=]
> drivers/xen/privcmd.c:1258:67: warning: array subscript i is outside array bounds of 'struct ioreq_port[0]' [-Warray-bounds=]
> 
> This results in no differences in binary output.
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Reviewed-by: Juergen Gross <jgross@suse.com>


Juergen


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