| Message ID | 20230808144216.2656505-1-stefanha@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] vfio: align capability structures | expand |
On Tue, 8 Aug 2023 10:42:16 -0400 Stefan Hajnoczi <stefanha@redhat.com> wrote: > The VFIO_DEVICE_GET_INFO, VFIO_DEVICE_GET_REGION_INFO, and > VFIO_IOMMU_GET_INFO ioctls fill in an info struct followed by capability > structs: > > +------+---------+---------+-----+ > | info | caps[0] | caps[1] | ... | > +------+---------+---------+-----+ > > Both the info and capability struct sizes are not always multiples of > sizeof(u64), leaving u64 fields in later capability structs misaligned. > > Userspace applications currently need to handle misalignment manually in > order to support CPU architectures and programming languages with strict > alignment requirements. > > Make life easier for userspace by ensuring alignment in the kernel. This > is done by padding info struct definitions and by copying out zeroes > after capability structs that are not aligned. > > The new layout is as follows: > > +------+---------+---+---------+-----+ > | info | caps[0] | 0 | caps[1] | ... | > +------+---------+---+---------+-----+ > > In this example caps[0] has a size that is not multiples of sizeof(u64), > so zero padding is added to align the subsequent structure. > > Adding zero padding between structs does not break the uapi. The memory > layout is specified by the info.cap_offset and caps[i].next fields > filled in by the kernel. Applications use these field values to locate > structs and are therefore unaffected by the addition of zero padding. > > Note that code that copies out info structs with padding is updated to > always zero the struct and copy out as many bytes as userspace > requested. This makes the code shorter and avoids potential information > leaks by ensuring padding is initialized. > > Originally-by: Alex Williamson <alex.williamson@redhat.com> > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> > --- > v2: > - Simplify padding approach as suggested by Alex > > include/uapi/linux/vfio.h | 2 ++ > drivers/vfio/pci/vfio_pci_core.c | 11 ++--------- > drivers/vfio/vfio_iommu_type1.c | 11 ++--------- > drivers/vfio/vfio_main.c | 6 ++++++ > 4 files changed, 12 insertions(+), 18 deletions(-) > > diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h > index 20c804bdc09c..8fe85f5c7b61 100644 > --- a/include/uapi/linux/vfio.h > +++ b/include/uapi/linux/vfio.h > @@ -217,6 +217,7 @@ struct vfio_device_info { > __u32 num_regions; /* Max region index + 1 */ > __u32 num_irqs; /* Max IRQ index + 1 */ > __u32 cap_offset; /* Offset within info struct of first cap */ > + __u32 pad; > }; > #define VFIO_DEVICE_GET_INFO _IO(VFIO_TYPE, VFIO_BASE + 7) > > @@ -1304,6 +1305,7 @@ struct vfio_iommu_type1_info { > #define VFIO_IOMMU_INFO_CAPS (1 << 1) /* Info supports caps */ > __u64 iova_pgsizes; /* Bitmap of supported page sizes */ > __u32 cap_offset; /* Offset within info struct of first cap */ > + __u32 pad; > }; > > /* > diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c > index 20d7b69ea6ff..e2ba2a350f6c 100644 > --- a/drivers/vfio/pci/vfio_pci_core.c > +++ b/drivers/vfio/pci/vfio_pci_core.c > @@ -920,24 +920,17 @@ static int vfio_pci_ioctl_get_info(struct vfio_pci_core_device *vdev, > struct vfio_device_info __user *arg) > { > unsigned long minsz = offsetofend(struct vfio_device_info, num_irqs); > - struct vfio_device_info info; > + struct vfio_device_info info = {}; > struct vfio_info_cap caps = { .buf = NULL, .size = 0 }; > - unsigned long capsz; > int ret; > > - /* For backward compatibility, cannot require this */ > - capsz = offsetofend(struct vfio_iommu_type1_info, cap_offset); > - > if (copy_from_user(&info, arg, minsz)) > return -EFAULT; > > if (info.argsz < minsz) > return -EINVAL; > > - if (info.argsz >= capsz) { > - minsz = capsz; > - info.cap_offset = 0; > - } > + minsz = min_t(size_t, info.argsz, sizeof(info)); Thanks for catching these, LGTM. I'll see if anyone else offers a review in the next couple days and otherwise apply this and 20230801155352.1391945-1-stefanha@redhat.com this week. Thanks, Alex > > info.flags = VFIO_DEVICE_FLAGS_PCI; > > diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c > index ebe0ad31d0b0..f812c475a626 100644 > --- a/drivers/vfio/vfio_iommu_type1.c > +++ b/drivers/vfio/vfio_iommu_type1.c > @@ -2762,27 +2762,20 @@ static int vfio_iommu_dma_avail_build_caps(struct vfio_iommu *iommu, > static int vfio_iommu_type1_get_info(struct vfio_iommu *iommu, > unsigned long arg) > { > - struct vfio_iommu_type1_info info; > + struct vfio_iommu_type1_info info = {}; > unsigned long minsz; > struct vfio_info_cap caps = { .buf = NULL, .size = 0 }; > - unsigned long capsz; > int ret; > > minsz = offsetofend(struct vfio_iommu_type1_info, iova_pgsizes); > > - /* For backward compatibility, cannot require this */ > - capsz = offsetofend(struct vfio_iommu_type1_info, cap_offset); > - > if (copy_from_user(&info, (void __user *)arg, minsz)) > return -EFAULT; > > if (info.argsz < minsz) > return -EINVAL; > > - if (info.argsz >= capsz) { > - minsz = capsz; > - info.cap_offset = 0; /* output, no-recopy necessary */ > - } > + minsz = min_t(size_t, info.argsz, sizeof(info)); > > mutex_lock(&iommu->lock); > info.flags = VFIO_IOMMU_INFO_PGSIZES; > diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c > index f0ca33b2e1df..2850478301d2 100644 > --- a/drivers/vfio/vfio_main.c > +++ b/drivers/vfio/vfio_main.c > @@ -1172,6 +1172,9 @@ struct vfio_info_cap_header *vfio_info_cap_add(struct vfio_info_cap *caps, > void *buf; > struct vfio_info_cap_header *header, *tmp; > > + /* Ensure that the next capability struct will be aligned */ > + size = ALIGN(size, sizeof(u64)); > + > buf = krealloc(caps->buf, caps->size + size, GFP_KERNEL); > if (!buf) { > kfree(caps->buf); > @@ -1205,6 +1208,9 @@ void vfio_info_cap_shift(struct vfio_info_cap *caps, size_t offset) > struct vfio_info_cap_header *tmp; > void *buf = (void *)caps->buf; > > + /* Capability structs should start with proper alignment */ > + WARN_ON(!IS_ALIGNED(offset, sizeof(u64))); > + > for (tmp = buf; tmp->next; tmp = buf + tmp->next - offset) > tmp->next += offset; > }
> From: Stefan Hajnoczi <stefanha@redhat.com> > Sent: Tuesday, August 8, 2023 10:42 PM > > The VFIO_DEVICE_GET_INFO, VFIO_DEVICE_GET_REGION_INFO, and > VFIO_IOMMU_GET_INFO ioctls fill in an info struct followed by capability > structs: > > +------+---------+---------+-----+ > | info | caps[0] | caps[1] | ... | > +------+---------+---------+-----+ > > Both the info and capability struct sizes are not always multiples of > sizeof(u64), leaving u64 fields in later capability structs misaligned. > > Userspace applications currently need to handle misalignment manually in > order to support CPU architectures and programming languages with strict > alignment requirements. > > Make life easier for userspace by ensuring alignment in the kernel. This > is done by padding info struct definitions and by copying out zeroes > after capability structs that are not aligned. > > The new layout is as follows: > > +------+---------+---+---------+-----+ > | info | caps[0] | 0 | caps[1] | ... | > +------+---------+---+---------+-----+ > > In this example caps[0] has a size that is not multiples of sizeof(u64), > so zero padding is added to align the subsequent structure. > > Adding zero padding between structs does not break the uapi. The memory > layout is specified by the info.cap_offset and caps[i].next fields > filled in by the kernel. Applications use these field values to locate > structs and are therefore unaffected by the addition of zero padding. > > Note that code that copies out info structs with padding is updated to > always zero the struct and copy out as many bytes as userspace > requested. This makes the code shorter and avoids potential information > leaks by ensuring padding is initialized. > > Originally-by: Alex Williamson <alex.williamson@redhat.com> > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> As Jason suggested let's also fix vfio_compat in iommufd. otherwise, Reviewed-by: Kevin Tian <kevin.tian@intel.com>
diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h index 20c804bdc09c..8fe85f5c7b61 100644 --- a/include/uapi/linux/vfio.h +++ b/include/uapi/linux/vfio.h @@ -217,6 +217,7 @@ struct vfio_device_info { __u32 num_regions; /* Max region index + 1 */ __u32 num_irqs; /* Max IRQ index + 1 */ __u32 cap_offset; /* Offset within info struct of first cap */ + __u32 pad; }; #define VFIO_DEVICE_GET_INFO _IO(VFIO_TYPE, VFIO_BASE + 7) @@ -1304,6 +1305,7 @@ struct vfio_iommu_type1_info { #define VFIO_IOMMU_INFO_CAPS (1 << 1) /* Info supports caps */ __u64 iova_pgsizes; /* Bitmap of supported page sizes */ __u32 cap_offset; /* Offset within info struct of first cap */ + __u32 pad; }; /* diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c index 20d7b69ea6ff..e2ba2a350f6c 100644 --- a/drivers/vfio/pci/vfio_pci_core.c +++ b/drivers/vfio/pci/vfio_pci_core.c @@ -920,24 +920,17 @@ static int vfio_pci_ioctl_get_info(struct vfio_pci_core_device *vdev, struct vfio_device_info __user *arg) { unsigned long minsz = offsetofend(struct vfio_device_info, num_irqs); - struct vfio_device_info info; + struct vfio_device_info info = {}; struct vfio_info_cap caps = { .buf = NULL, .size = 0 }; - unsigned long capsz; int ret; - /* For backward compatibility, cannot require this */ - capsz = offsetofend(struct vfio_iommu_type1_info, cap_offset); - if (copy_from_user(&info, arg, minsz)) return -EFAULT; if (info.argsz < minsz) return -EINVAL; - if (info.argsz >= capsz) { - minsz = capsz; - info.cap_offset = 0; - } + minsz = min_t(size_t, info.argsz, sizeof(info)); info.flags = VFIO_DEVICE_FLAGS_PCI; diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c index ebe0ad31d0b0..f812c475a626 100644 --- a/drivers/vfio/vfio_iommu_type1.c +++ b/drivers/vfio/vfio_iommu_type1.c @@ -2762,27 +2762,20 @@ static int vfio_iommu_dma_avail_build_caps(struct vfio_iommu *iommu, static int vfio_iommu_type1_get_info(struct vfio_iommu *iommu, unsigned long arg) { - struct vfio_iommu_type1_info info; + struct vfio_iommu_type1_info info = {}; unsigned long minsz; struct vfio_info_cap caps = { .buf = NULL, .size = 0 }; - unsigned long capsz; int ret; minsz = offsetofend(struct vfio_iommu_type1_info, iova_pgsizes); - /* For backward compatibility, cannot require this */ - capsz = offsetofend(struct vfio_iommu_type1_info, cap_offset); - if (copy_from_user(&info, (void __user *)arg, minsz)) return -EFAULT; if (info.argsz < minsz) return -EINVAL; - if (info.argsz >= capsz) { - minsz = capsz; - info.cap_offset = 0; /* output, no-recopy necessary */ - } + minsz = min_t(size_t, info.argsz, sizeof(info)); mutex_lock(&iommu->lock); info.flags = VFIO_IOMMU_INFO_PGSIZES; diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c index f0ca33b2e1df..2850478301d2 100644 --- a/drivers/vfio/vfio_main.c +++ b/drivers/vfio/vfio_main.c @@ -1172,6 +1172,9 @@ struct vfio_info_cap_header *vfio_info_cap_add(struct vfio_info_cap *caps, void *buf; struct vfio_info_cap_header *header, *tmp; + /* Ensure that the next capability struct will be aligned */ + size = ALIGN(size, sizeof(u64)); + buf = krealloc(caps->buf, caps->size + size, GFP_KERNEL); if (!buf) { kfree(caps->buf); @@ -1205,6 +1208,9 @@ void vfio_info_cap_shift(struct vfio_info_cap *caps, size_t offset) struct vfio_info_cap_header *tmp; void *buf = (void *)caps->buf; + /* Capability structs should start with proper alignment */ + WARN_ON(!IS_ALIGNED(offset, sizeof(u64))); + for (tmp = buf; tmp->next; tmp = buf + tmp->next - offset) tmp->next += offset; }
The VFIO_DEVICE_GET_INFO, VFIO_DEVICE_GET_REGION_INFO, and VFIO_IOMMU_GET_INFO ioctls fill in an info struct followed by capability structs: +------+---------+---------+-----+ | info | caps[0] | caps[1] | ... | +------+---------+---------+-----+ Both the info and capability struct sizes are not always multiples of sizeof(u64), leaving u64 fields in later capability structs misaligned. Userspace applications currently need to handle misalignment manually in order to support CPU architectures and programming languages with strict alignment requirements. Make life easier for userspace by ensuring alignment in the kernel. This is done by padding info struct definitions and by copying out zeroes after capability structs that are not aligned. The new layout is as follows: +------+---------+---+---------+-----+ | info | caps[0] | 0 | caps[1] | ... | +------+---------+---+---------+-----+ In this example caps[0] has a size that is not multiples of sizeof(u64), so zero padding is added to align the subsequent structure. Adding zero padding between structs does not break the uapi. The memory layout is specified by the info.cap_offset and caps[i].next fields filled in by the kernel. Applications use these field values to locate structs and are therefore unaffected by the addition of zero padding. Note that code that copies out info structs with padding is updated to always zero the struct and copy out as many bytes as userspace requested. This makes the code shorter and avoids potential information leaks by ensuring padding is initialized. Originally-by: Alex Williamson <alex.williamson@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> --- v2: - Simplify padding approach as suggested by Alex include/uapi/linux/vfio.h | 2 ++ drivers/vfio/pci/vfio_pci_core.c | 11 ++--------- drivers/vfio/vfio_iommu_type1.c | 11 ++--------- drivers/vfio/vfio_main.c | 6 ++++++ 4 files changed, 12 insertions(+), 18 deletions(-)