Re: [PATCH v6 01/15] hw/nvme: Use pcie_sriov_num_vfs()

[Kevin Wolf <kwolf@redhat.com>]

Am 20.02.2024 um 13:24 hat Akihiko Odaki geschrieben:
> nvme_sriov_pre_write_ctrl() used to directly inspect SR-IOV
> configurations to know the number of VFs being disabled due to SR-IOV
> configuration writes, but the logic was flawed and resulted in
> out-of-bound memory access.
> 
> It assumed PCI_SRIOV_NUM_VF always has the number of currently enabled
> VFs, but it actually doesn't in the following cases:
> - PCI_SRIOV_NUM_VF has been set but PCI_SRIOV_CTRL_VFE has never been.
> - PCI_SRIOV_NUM_VF was written after PCI_SRIOV_CTRL_VFE was set.
> - VFs were only partially enabled because of realization failure.
> 
> It is a responsibility of pcie_sriov to interpret SR-IOV configurations
> and pcie_sriov does it correctly, so use pcie_sriov_num_vfs(), which it
> provides, to get the number of enabled VFs before and after SR-IOV
> configuration writes.
> 
> Cc: qemu-stable@nongnu.org
> Fixes: CVE-2024-26328
> Fixes: 11871f53ef8e ("hw/nvme: Add support for the Virtualization Management command")
> Suggested-by: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
> ---
>  hw/nvme/ctrl.c | 26 ++++++++------------------
>  1 file changed, 8 insertions(+), 18 deletions(-)
> 
> diff --git a/hw/nvme/ctrl.c b/hw/nvme/ctrl.c
> index f026245d1e9e..7a56e7b79b4d 100644
> --- a/hw/nvme/ctrl.c
> +++ b/hw/nvme/ctrl.c
> @@ -8466,36 +8466,26 @@ static void nvme_pci_reset(DeviceState *qdev)
>      nvme_ctrl_reset(n, NVME_RESET_FUNCTION);
>  }
>  
> -static void nvme_sriov_pre_write_ctrl(PCIDevice *dev, uint32_t address,
> -                                      uint32_t val, int len)
> +static void nvme_sriov_post_write_config(PCIDevice *dev, uint16_t old_num_vfs)
>  {
>      NvmeCtrl *n = NVME(dev);
>      NvmeSecCtrlEntry *sctrl;
> -    uint16_t sriov_cap = dev->exp.sriov_cap;
> -    uint32_t off = address - sriov_cap;
> -    int i, num_vfs;
> +    int i;
>  
> -    if (!sriov_cap) {
> -        return;
> -    }
> -
> -    if (range_covers_byte(off, len, PCI_SRIOV_CTRL)) {
> -        if (!(val & PCI_SRIOV_CTRL_VFE)) {
> -            num_vfs = pci_get_word(dev->config + sriov_cap + PCI_SRIOV_NUM_VF);
> -            for (i = 0; i < num_vfs; i++) {
> -                sctrl = &n->sec_ctrl_list.sec[i];
> -                nvme_virt_set_state(n, le16_to_cpu(sctrl->scid), false);
> -            }
> -        }
> +    for (i = pcie_sriov_num_vfs(dev); i < old_num_vfs; i++) {
> +        sctrl = &n->sec_ctrl_list.sec[i];
> +        nvme_virt_set_state(n, le16_to_cpu(sctrl->scid), false);
>      }
>  }

Maybe I'm missing something, but if the concern is that 'i' could run
beyond the end of the array, I don't see anything that limits
pcie_sriov_num_vfs() to the static size of 127 that n->sec_ctrl_list.sec
has. register_vfs() seems to just take whatever 16 bit value the guest
wrote without imposing additional restrictions.

If there is some mechanism that makes register_vf() fail if we exceed
the limit, maybe an assertion with a comment would be in order because
it doesn't seem obvious. I couldn't find any code that enforces it,
sriov_max_vfs only ever seems to be used as a hint for the guest.

If not, do we need another check that fails gracefully in the error
case?

Kevin