[v2] hw/s390/ccw.c: Don't take address of packed members

Message ID 20181213120252.21697-1-peter.maydell@linaro.org
State New
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Series
  • [v2] hw/s390/ccw.c: Don't take address of packed members
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Commit Message

Peter Maydell Dec. 13, 2018, 12:02 p.m.
Taking the address of a field in a packed struct is a bad idea, because
it might not be actually aligned enough for that pointer type (and
thus cause a crash on dereference on some host architectures). Newer
versions of clang warn about this.

Avoid the problem by using local copies of the PMCW and SCSW
struct fields in copy_schib_from_guest() and copy_schib_to_guest().

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

---
v1->v2 changes:
 * add comment about why we're using locals
 * name locals with underscores, as QEMU's naming conventions recommend


 hw/s390x/css.c | 28 ++++++++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

-- 
2.19.2

Comments

Farhan Ali Dec. 13, 2018, 1 p.m. | #1
On 12/13/2018 07:02 AM, Peter Maydell wrote:
> Taking the address of a field in a packed struct is a bad idea, because

> it might not be actually aligned enough for that pointer type (and

> thus cause a crash on dereference on some host architectures). Newer

> versions of clang warn about this.

> 

> Avoid the problem by using local copies of the PMCW and SCSW

> struct fields in copy_schib_from_guest() and copy_schib_to_guest().

> 

> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

> ---

> v1->v2 changes:

>   * add comment about why we're using locals

>   * name locals with underscores, as QEMU's naming conventions recommend

> 

> 

>   hw/s390x/css.c | 28 ++++++++++++++++++++++++----

>   1 file changed, 24 insertions(+), 4 deletions(-)

> 

> diff --git a/hw/s390x/css.c b/hw/s390x/css.c

> index 04ec5cc9705..f92b046cd33 100644

> --- a/hw/s390x/css.c

> +++ b/hw/s390x/css.c

> @@ -1290,9 +1290,19 @@ void copy_scsw_to_guest(SCSW *dest, const SCSW *src)

>   static void copy_schib_to_guest(SCHIB *dest, const SCHIB *src)

>   {

>       int i;

> +    /*

> +     * We copy the PMCW and SCSW in and out of local variables to

> +     * avoid taking the address of members of a packed struct.

> +     */

> +    PMCW src_pmcw, dest_pmcw;

> +    SCSW src_scsw, dest_scsw;

>   

> -    copy_pmcw_to_guest(&dest->pmcw, &src->pmcw);

> -    copy_scsw_to_guest(&dest->scsw, &src->scsw);

> +    src_pmcw = src->pmcw;

> +    copy_pmcw_to_guest(&dest_pmcw, &src_pmcw);

> +    dest->pmcw = dest_pmcw;

> +    src_scsw = src->scsw;

> +    copy_scsw_to_guest(&dest_scsw, &src_scsw);

> +    dest->scsw = dest_scsw;

>       dest->mba = cpu_to_be64(src->mba);

>       for (i = 0; i < ARRAY_SIZE(dest->mda); i++) {

>           dest->mda[i] = src->mda[i];

> @@ -1339,9 +1349,19 @@ static void copy_scsw_from_guest(SCSW *dest, const SCSW *src)

>   static void copy_schib_from_guest(SCHIB *dest, const SCHIB *src)

>   {

>       int i;

> +    /*

> +     * We copy the PMCW and SCSW in and out of local variables to

> +     * avoid taking the address of members of a packed struct.

> +     */

> +    PMCW src_pmcw, dest_pmcw;

> +    SCSW src_scsw, dest_scsw;

>   

> -    copy_pmcw_from_guest(&dest->pmcw, &src->pmcw);

> -    copy_scsw_from_guest(&dest->scsw, &src->scsw);

> +    src_pmcw = src->pmcw;

> +    copy_pmcw_from_guest(&dest_pmcw, &src_pmcw);

> +    dest->pmcw = dest_pmcw;

> +    src_scsw = src->scsw;

> +    copy_scsw_from_guest(&dest_scsw, &src_scsw);

> +    dest->scsw = dest_scsw;

>       dest->mba = be64_to_cpu(src->mba);

>       for (i = 0; i < ARRAY_SIZE(dest->mda); i++) {

>           dest->mda[i] = src->mda[i];

> 


Reviewed-by: Farhan Ali <alifm@linux.ibm.com>
Cornelia Huck Dec. 13, 2018, 2:56 p.m. | #2
On Thu, 13 Dec 2018 12:02:52 +0000
Peter Maydell <peter.maydell@linaro.org> wrote:

> Taking the address of a field in a packed struct is a bad idea, because

> it might not be actually aligned enough for that pointer type (and

> thus cause a crash on dereference on some host architectures). Newer

> versions of clang warn about this.

> 

> Avoid the problem by using local copies of the PMCW and SCSW

> struct fields in copy_schib_from_guest() and copy_schib_to_guest().

> 

> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

> ---

> v1->v2 changes:

>  * add comment about why we're using locals

>  * name locals with underscores, as QEMU's naming conventions recommend

> 

> 

>  hw/s390x/css.c | 28 ++++++++++++++++++++++++----

>  1 file changed, 24 insertions(+), 4 deletions(-)


Thanks, applied.
Thomas Huth Dec. 13, 2018, 8:06 p.m. | #3
On 2018-12-13 13:02, Peter Maydell wrote:
> Taking the address of a field in a packed struct is a bad idea, because

> it might not be actually aligned enough for that pointer type (and

> thus cause a crash on dereference on some host architectures). Newer

> versions of clang warn about this.

> 

> Avoid the problem by using local copies of the PMCW and SCSW

> struct fields in copy_schib_from_guest() and copy_schib_to_guest().

> 

> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

> ---

> v1->v2 changes:

>  * add comment about why we're using locals


Thanks!

Reviewed-by: Thomas Huth <thuth@redhat.com>

Patch

diff --git a/hw/s390x/css.c b/hw/s390x/css.c
index 04ec5cc9705..f92b046cd33 100644
--- a/hw/s390x/css.c
+++ b/hw/s390x/css.c
@@ -1290,9 +1290,19 @@  void copy_scsw_to_guest(SCSW *dest, const SCSW *src)
 static void copy_schib_to_guest(SCHIB *dest, const SCHIB *src)
 {
     int i;
+    /*
+     * We copy the PMCW and SCSW in and out of local variables to
+     * avoid taking the address of members of a packed struct.
+     */
+    PMCW src_pmcw, dest_pmcw;
+    SCSW src_scsw, dest_scsw;
 
-    copy_pmcw_to_guest(&dest->pmcw, &src->pmcw);
-    copy_scsw_to_guest(&dest->scsw, &src->scsw);
+    src_pmcw = src->pmcw;
+    copy_pmcw_to_guest(&dest_pmcw, &src_pmcw);
+    dest->pmcw = dest_pmcw;
+    src_scsw = src->scsw;
+    copy_scsw_to_guest(&dest_scsw, &src_scsw);
+    dest->scsw = dest_scsw;
     dest->mba = cpu_to_be64(src->mba);
     for (i = 0; i < ARRAY_SIZE(dest->mda); i++) {
         dest->mda[i] = src->mda[i];
@@ -1339,9 +1349,19 @@  static void copy_scsw_from_guest(SCSW *dest, const SCSW *src)
 static void copy_schib_from_guest(SCHIB *dest, const SCHIB *src)
 {
     int i;
+    /*
+     * We copy the PMCW and SCSW in and out of local variables to
+     * avoid taking the address of members of a packed struct.
+     */
+    PMCW src_pmcw, dest_pmcw;
+    SCSW src_scsw, dest_scsw;
 
-    copy_pmcw_from_guest(&dest->pmcw, &src->pmcw);
-    copy_scsw_from_guest(&dest->scsw, &src->scsw);
+    src_pmcw = src->pmcw;
+    copy_pmcw_from_guest(&dest_pmcw, &src_pmcw);
+    dest->pmcw = dest_pmcw;
+    src_scsw = src->scsw;
+    copy_scsw_from_guest(&dest_scsw, &src_scsw);
+    dest->scsw = dest_scsw;
     dest->mba = be64_to_cpu(src->mba);
     for (i = 0; i < ARRAY_SIZE(dest->mda); i++) {
         dest->mda[i] = src->mda[i];