On Mon, 8 Oct 2018 13:06:20 -0500 Wenwen Wang <[email protected]> wrote:
> In vfio_spapr_iommu_eeh_ioctl(), if the ioctl command is VFIO_EEH_PE_OP, > the user-space buffer 'arg' is copied to the kernel object 'op' and the > 'argsz' and 'flags' fields of 'op' are checked. If the check fails, an > error code EINVAL is returned. Otherwise, 'op.op' is further checked > through a switch statement to invoke related handlers. If 'op.op' is > VFIO_EEH_PE_INJECT_ERR, the whole user-space buffer 'arg' is copied again > to 'op' to obtain the err information. However, in the following execution > of this case, the fields of 'op', except the field 'err', are actually not > used. That is, the second copy has a redundant part. Therefore, for both > performance consideration, the redundant part of the second copy should be > removed. > > This patch removes such a part in the second copy. It only copies from > 'err.type' to 'err.mask', which is exactly required by the > VFIO_EEH_PE_INJECT_ERR op. > > Signed-off-by: Wenwen Wang <[email protected]> > --- > drivers/vfio/vfio_spapr_eeh.c | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 deletions(-) > > diff --git a/drivers/vfio/vfio_spapr_eeh.c b/drivers/vfio/vfio_spapr_eeh.c > index 38edeb4..66634c6 100644 > --- a/drivers/vfio/vfio_spapr_eeh.c > +++ b/drivers/vfio/vfio_spapr_eeh.c > @@ -37,6 +37,7 @@ long vfio_spapr_iommu_eeh_ioctl(struct iommu_group *group, > struct eeh_pe *pe; > struct vfio_eeh_pe_op op; > unsigned long minsz; > + unsigned long start, end; > long ret = -EINVAL; > > switch (cmd) { > @@ -86,10 +87,12 @@ long vfio_spapr_iommu_eeh_ioctl(struct iommu_group *group, > ret = eeh_pe_configure(pe); > break; > case VFIO_EEH_PE_INJECT_ERR: > - minsz = offsetofend(struct vfio_eeh_pe_op, err.mask); > - if (op.argsz < minsz) > + start = offsetof(struct vfio_eeh_pe_op, err.type); We already have this in minsz, offsetofend(,op) == offsetof(,err.type). That can't change without breaking userspace. > + end = offsetofend(struct vfio_eeh_pe_op, err.mask); > + if (op.argsz < end) > return -EINVAL; > - if (copy_from_user(&op, (void __user *)arg, minsz)) > + if (copy_from_user(&op.err, (char __user *)arg + > + start, end - start)) So we trade 12 bytes of redundant copy for an extra stack variable and an arithmetic operation, not necessarily an obvious win, but more correct I guess. Alexey, I also notice that these 12 bytes means that the u64 fields in struct vfio_eeh_pe_err are not 8-byte aligned which could lead to compiler dependent packing interpretation issues with userspace. Should there be a 4-byte reserved field in there to make it explicit (so long as it matches the current interpretation)? Thanks, Alex
