| Message ID | 20230424151919.1333299-1-peter.maydell@linaro.org |
|---|---|
| State | Superseded |
| Headers | show |
| Series | hw/net/msf2-emac: Don't modify descriptor in-place in emac_store_desc() | expand |
On 24/04/2023 17.19, Peter Maydell wrote: > The msf2-emac ethernet controller has functions emac_load_desc() and > emac_store_desc() which read and write the in-memory descriptor > blocks and handle conversion between guest and host endianness. > > As currently written, emac_store_desc() does the endianness > conversion in-place; this means that it effectively consumes the > input EmacDesc struct, because on a big-endian host the fields will > be overwritten with the little-endian versions of their values. > Unfortunately, in all the callsites the code continues to access > fields in the EmacDesc struct after it has called emac_store_desc() > -- specifically, it looks at the d.next field. > > The effect of this is that on a big-endian host networking doesn't > work because the address of the next descriptor is corrupted. > > We could fix this by making the callsite avoid using the struct; but > it's more robust to have emac_store_desc() leave its input alone. > > (emac_load_desc() also does an in-place conversion, but here this is > fine, because the function is supposed to be initializing the > struct.) > > Cc: qemu-stable@nongnu.org > Signed-off-by: Peter Maydell <peter.maydell@linaro.org> > --- > This is one of a number of issues that prevent 'make check-avocado' > working for arm targets on a big-endian host... > > hw/net/msf2-emac.c | 14 +++++++++----- > 1 file changed, 9 insertions(+), 5 deletions(-) > > diff --git a/hw/net/msf2-emac.c b/hw/net/msf2-emac.c > index 7ccd3e51427..34c1f768db0 100644 > --- a/hw/net/msf2-emac.c > +++ b/hw/net/msf2-emac.c > @@ -120,12 +120,16 @@ static void emac_load_desc(MSF2EmacState *s, EmacDesc *d, hwaddr desc) > > static void emac_store_desc(MSF2EmacState *s, EmacDesc *d, hwaddr desc) You could likely also add a "const" to "EmacDesc *d" now. > { > - /* Convert from host endianness into LE. */ > - d->pktaddr = cpu_to_le32(d->pktaddr); > - d->pktsize = cpu_to_le32(d->pktsize); > - d->next = cpu_to_le32(d->next); > + EmacDesc outd; > + /* > + * Convert from host endianness into LE. We use a local struct because > + * calling code may still want to look at the fields afterwards. > + */ > + outd.pktaddr = cpu_to_le32(d->pktaddr); > + outd.pktsize = cpu_to_le32(d->pktsize); > + outd.next = cpu_to_le32(d->next); > > - address_space_write(&s->dma_as, desc, MEMTXATTRS_UNSPECIFIED, d, sizeof *d); > + address_space_write(&s->dma_as, desc, MEMTXATTRS_UNSPECIFIED, &outd, sizeof outd); > } Reviewed-by: Thomas Huth <thuth@redhat.com>
On Mon, 24 Apr 2023 at 17:27, Thomas Huth <thuth@redhat.com> wrote: > > On 24/04/2023 17.19, Peter Maydell wrote: > > The msf2-emac ethernet controller has functions emac_load_desc() and > > emac_store_desc() which read and write the in-memory descriptor > > blocks and handle conversion between guest and host endianness. > > > > As currently written, emac_store_desc() does the endianness > > conversion in-place; this means that it effectively consumes the > > input EmacDesc struct, because on a big-endian host the fields will > > be overwritten with the little-endian versions of their values. > > Unfortunately, in all the callsites the code continues to access > > fields in the EmacDesc struct after it has called emac_store_desc() > > -- specifically, it looks at the d.next field. > > > > The effect of this is that on a big-endian host networking doesn't > > work because the address of the next descriptor is corrupted. > > > > We could fix this by making the callsite avoid using the struct; but > > it's more robust to have emac_store_desc() leave its input alone. > > > > (emac_load_desc() also does an in-place conversion, but here this is > > fine, because the function is supposed to be initializing the > > struct.) > > > > Cc: qemu-stable@nongnu.org > > Signed-off-by: Peter Maydell <peter.maydell@linaro.org> > > --- > > This is one of a number of issues that prevent 'make check-avocado' > > working for arm targets on a big-endian host... > > > > hw/net/msf2-emac.c | 14 +++++++++----- > > 1 file changed, 9 insertions(+), 5 deletions(-) > > > > diff --git a/hw/net/msf2-emac.c b/hw/net/msf2-emac.c > > index 7ccd3e51427..34c1f768db0 100644 > > --- a/hw/net/msf2-emac.c > > +++ b/hw/net/msf2-emac.c > > @@ -120,12 +120,16 @@ static void emac_load_desc(MSF2EmacState *s, EmacDesc *d, hwaddr desc) > > > > static void emac_store_desc(MSF2EmacState *s, EmacDesc *d, hwaddr desc) > > You could likely also add a "const" to "EmacDesc *d" now. Yep; applied to target-arm.next with that change added. -- PMM
diff --git a/hw/net/msf2-emac.c b/hw/net/msf2-emac.c index 7ccd3e51427..34c1f768db0 100644 --- a/hw/net/msf2-emac.c +++ b/hw/net/msf2-emac.c @@ -120,12 +120,16 @@ static void emac_load_desc(MSF2EmacState *s, EmacDesc *d, hwaddr desc) static void emac_store_desc(MSF2EmacState *s, EmacDesc *d, hwaddr desc) { - /* Convert from host endianness into LE. */ - d->pktaddr = cpu_to_le32(d->pktaddr); - d->pktsize = cpu_to_le32(d->pktsize); - d->next = cpu_to_le32(d->next); + EmacDesc outd; + /* + * Convert from host endianness into LE. We use a local struct because + * calling code may still want to look at the fields afterwards. + */ + outd.pktaddr = cpu_to_le32(d->pktaddr); + outd.pktsize = cpu_to_le32(d->pktsize); + outd.next = cpu_to_le32(d->next); - address_space_write(&s->dma_as, desc, MEMTXATTRS_UNSPECIFIED, d, sizeof *d); + address_space_write(&s->dma_as, desc, MEMTXATTRS_UNSPECIFIED, &outd, sizeof outd); } static void msf2_dma_tx(MSF2EmacState *s)
The msf2-emac ethernet controller has functions emac_load_desc() and emac_store_desc() which read and write the in-memory descriptor blocks and handle conversion between guest and host endianness. As currently written, emac_store_desc() does the endianness conversion in-place; this means that it effectively consumes the input EmacDesc struct, because on a big-endian host the fields will be overwritten with the little-endian versions of their values. Unfortunately, in all the callsites the code continues to access fields in the EmacDesc struct after it has called emac_store_desc() -- specifically, it looks at the d.next field. The effect of this is that on a big-endian host networking doesn't work because the address of the next descriptor is corrupted. We could fix this by making the callsite avoid using the struct; but it's more robust to have emac_store_desc() leave its input alone. (emac_load_desc() also does an in-place conversion, but here this is fine, because the function is supposed to be initializing the struct.) Cc: qemu-stable@nongnu.org Signed-off-by: Peter Maydell <peter.maydell@linaro.org> --- This is one of a number of issues that prevent 'make check-avocado' working for arm targets on a big-endian host... hw/net/msf2-emac.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-)