| Message ID | 20181213120252.21697-1-peter.maydell@linaro.org |
|---|---|
| State | Accepted |
| Headers | show |
| Series | [v2] hw/s390/ccw.c: Don't take address of packed members | expand |
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>
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.
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>
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];
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