Ping^2 ? thanks -- PMM
On Mon, 20 Jul 2026 at 09:42, Peter Maydell <[email protected]> wrote: > > Ping -- would anybody on the qemu-block side like to review this? > > thanks > -- PMM > > On Tue, 30 Jun 2026 at 11:42, Peter Maydell <[email protected]> wrote: > > > > In ide_set_sector() if we're using CHS addressing the way we update > > the drive state involves dividing by (s->heads * s->sectors). These > > values can be set by the guest using the INITIALIZE DRIVE PARAMETERS > > command, which means that s->sectors can be 0. (s->heads can't be 0 > > because the command passes a heads-1 value.) INITIALIZE DRIVE > > PARAMETERS is specified to not check the input values for validity; > > instead no error is posted until some other command makes an illegal > > access. So we have to cope with a 0 divisor here. > > > > Special-case s->sectors being zero. > > > > Cc: [email protected] > > Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/2399 > > Signed-off-by: Peter Maydell <[email protected]> > > --- > > We don't seem to ever actually check that the guest's read/write ops > > are within the CHS limits it sets with INITIALIZE DRIVE PARAMETERS -- > > ide_sect_range_ok() only checks against the underlying block device > > geometry. Maybe we should? Then a zero-sectors misconfig would > > result in our reporting the error on the read/write as the spec > > suggests we should. This patch fixes the division-by-zero, at least, > > though. > > --- > > hw/ide/core.c | 28 +++++++++++++++++++++------- > > 1 file changed, 21 insertions(+), 7 deletions(-) > > > > diff --git a/hw/ide/core.c b/hw/ide/core.c > > index f78b00220b..b030531534 100644 > > --- a/hw/ide/core.c > > +++ b/hw/ide/core.c > > @@ -646,13 +646,27 @@ void ide_set_sector(IDEState *s, int64_t sector_num) > > } > > } else { > > /* CHS */ > > - cyl = sector_num / (s->heads * s->sectors); > > - r = sector_num % (s->heads * s->sectors); > > - s->hcyl = cyl >> 8; > > - s->lcyl = cyl; > > - s->select = (s->select & ~(ATA_DEV_HS)) | > > - ((r / s->sectors) & (ATA_DEV_HS)); > > - s->sector = (r % s->sectors) + 1; > > + if (s->sectors == 0) { > > + /* > > + * s->sectors is under guest control via INITIALIZE DRIVE > > + * PARAMETERS and can be 0; this is an error but can't > > + * be reported at INITIALIZE DRIVE PARAMETERS time so we > > + * have to cope with the bad value here. > > + * (s->heads is always at least 1.) > > + */ > > + s->hcyl = 0; > > + s->lcyl = 0; > > + s->select = s->select & ~(ATA_DEV_HS); > > + s->sector = 1; > > + } else { > > + cyl = sector_num / (s->heads * s->sectors); > > + r = sector_num % (s->heads * s->sectors); > > + s->hcyl = cyl >> 8; > > + s->lcyl = cyl; > > + s->select = (s->select & ~(ATA_DEV_HS)) | > > + ((r / s->sectors) & (ATA_DEV_HS)); > > + s->sector = (r % s->sectors) + 1; > > + } > > } > > }
