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Tsirkin" To: Keir Fraser Cc: Jason Wang , kernel-team@android.com, virtualization , linux-kernel Subject: Re: [PATCH v2] virtio: pci: sanity check bar indexes Message-ID: <20220323092254-mutt-send-email-mst@kernel.org> References: <20220322151952.2950143-1-keirf@google.com> <20220323075030-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 23, 2022 at 01:21:55PM +0000, Keir Fraser wrote: > On Wed, Mar 23, 2022 at 08:01:42AM -0400, Michael S. Tsirkin wrote: > > On Wed, Mar 23, 2022 at 03:57:59PM +0800, Jason Wang wrote: > > > On Tue, Mar 22, 2022 at 11:20 PM Keir Fraser wrote: > > > > > > > > The bar index is used as an index into the device's resource list > > > > and should be checked as within range for a standard bar. > > > > > > > > Also clean up an existing check to consistently use PCI_STD_NUM_BARS. > > > > > > > > Signed-off-by: Keir Fraser > > > > --- > > > > drivers/virtio/virtio_pci_modern.c | 10 ++++++++-- > > > > drivers/virtio/virtio_pci_modern_dev.c | 8 +++++++- > > > > 2 files changed, 15 insertions(+), 3 deletions(-) > > > > > > > > diff --git a/drivers/virtio/virtio_pci_modern.c b/drivers/virtio/virtio_pci_modern.c > > > > index 5455bc041fb6..84bace98dff5 100644 > > > > --- a/drivers/virtio/virtio_pci_modern.c > > > > +++ b/drivers/virtio/virtio_pci_modern.c > > > > @@ -293,7 +293,7 @@ static int virtio_pci_find_shm_cap(struct pci_dev *dev, u8 required_id, > > > > > > > > for (pos = pci_find_capability(dev, PCI_CAP_ID_VNDR); pos > 0; > > > > pos = pci_find_next_capability(dev, pos, PCI_CAP_ID_VNDR)) { > > > > - u8 type, cap_len, id; > > > > + u8 type, cap_len, id, res_bar; > > > > u32 tmp32; > > > > u64 res_offset, res_length; > > > > > > > > @@ -317,7 +317,12 @@ static int virtio_pci_find_shm_cap(struct pci_dev *dev, u8 required_id, > > > > > > > > /* Type, and ID match, looks good */ > > > > pci_read_config_byte(dev, pos + offsetof(struct virtio_pci_cap, > > > > - bar), bar); > > > > + bar), &res_bar); > > > > + if (res_bar >= PCI_STD_NUM_BARS) { > > > > + dev_err(&dev->dev, "%s: shm cap with bad bar: %d\n", > > > > + __func__, res_bar); > > > > + continue; > > > > + } > > > > > > > > /* Read the lower 32bit of length and offset */ > > > > pci_read_config_dword(dev, pos + offsetof(struct virtio_pci_cap, > > > > In fact, the spec says such BAR values are reserved, not bad, so > > the capabiluty should be ignored, they should not cause the driver to error out > > or print errors. > > Ah yes, so I see. It makes sense then to silently ignore the capability and print nothing. > I will fix it. > > > > > @@ -337,6 +342,7 @@ static int virtio_pci_find_shm_cap(struct pci_dev *dev, u8 required_id, > > > > length_hi), &tmp32); > > > > res_length |= ((u64)tmp32) << 32; > > > > > > > > + *bar = res_bar; > > > > *offset = res_offset; > > > > *len = res_length; > > > > > > > > diff --git a/drivers/virtio/virtio_pci_modern_dev.c b/drivers/virtio/virtio_pci_modern_dev.c > > > > index e8b3ff2b9fbc..a6911d1e212a 100644 > > > > --- a/drivers/virtio/virtio_pci_modern_dev.c > > > > +++ b/drivers/virtio/virtio_pci_modern_dev.c > > > > @@ -35,6 +35,12 @@ vp_modern_map_capability(struct virtio_pci_modern_device *mdev, int off, > > > > pci_read_config_dword(dev, off + offsetof(struct virtio_pci_cap, length), > > > > &length); > > > > > > > > + if (bar >= PCI_STD_NUM_BARS) { > > > > + dev_err(&dev->dev, > > > > + "virtio_pci: bad capability bar %u\n", bar); > > > > In fact, I would say the issue is less that bar is reserved. > > The real issue is that the value apparently changed since > > we read it the first time. I think it's a good idea to > > reflect that in the message. Maybe find_capability should return > > the capability structure so we don't need to re-read it from > > the device? > > I will have a look and fix it up one way or the other, and respin > this patch. > > Thanks, > Keir BTW avoiding extra reads is good for start up speed. This is slow path, but still. > > > > + return NULL; > > > > + } > > > > + > > > > if (length <= start) { > > > > dev_err(&dev->dev, > > > > "virtio_pci: bad capability len %u (>%u expected)\n", > > > > @@ -120,7 +126,7 @@ static inline int virtio_pci_find_capability(struct pci_dev *dev, u8 cfg_type, > > > > &bar); > > > > > > > > /* Ignore structures with reserved BAR values */ > > > > - if (bar > 0x5) > > > > + if (bar >= PCI_STD_NUM_BARS) > > > > continue; > > > > > > Just notice that the spec said: > > > > > > " > > > values 0x0 to 0x5 specify a Base Address register (BAR) belonging to > > > the function located beginning at 10h in PCI Configuration Space and > > > used to map the structure into Memory or I/O Space. The BAR is > > > permitted to be either 32-bit or 64-bit, it can map Memory Space or > > > I/O Space. > > > > > > Any other value is reserved for future use. > > > " > > > So we probably need to stick 0x5 instead of 0x6 (PCI_STD_NUM_BARS) for > > > this and other places. > > > > > > Thanks > > > > It does not matter much IMHO, the reason spec uses 0 to 0x5 is precisely > > because that's the standard number of BARs. Both ways work as long as we > > are consistent, and I guess PCI_STD_NUM_BARS might be preferable since > > people tend to copy paste values. > > > > > > > > > > if (type == cfg_type) { > > > > -- > > > > 2.35.1.894.gb6a874cedc-goog > > > > > >