Re: [PATCH] PCI: dwc: fix find_next_bit() usage

[Bjorn Andersson]

On Wed, Sep 4, 2019 at 9:03 AM Niklas Cassel <niklas.cassel@xxxxxxxxxx> wrote:
>
> find_next_bit() takes a parameter of size long, and performs arithmetic
> that assumes that the argument is of size long.
>
> Therefore we cannot pass a u32, since this will cause find_next_bit()
> to read outside the stack buffer and will produce the following print:
> BUG: KASAN: stack-out-of-bounds in find_next_bit+0x38/0xb0
>
> Fixes: 1b497e6493c4 ("PCI: dwc: Fix uninitialized variable in dw_handle_msi_irq()")
> Signed-off-by: Niklas Cassel <niklas.cassel@xxxxxxxxxx>

Tested-by: Bjorn Andersson <bjorn.andersson@xxxxxxxxxx>

> ---
>  drivers/pci/controller/dwc/pcie-designware-host.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> index d3156446ff27..45f21640c977 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> @@ -78,7 +78,8 @@ static struct msi_domain_info dw_pcie_msi_domain_info = {
>  irqreturn_t dw_handle_msi_irq(struct pcie_port *pp)
>  {
>         int i, pos, irq;
> -       u32 val, num_ctrls;
> +       unsigned long val;
> +       u32 status, num_ctrls;
>         irqreturn_t ret = IRQ_NONE;
>
>         num_ctrls = pp->num_vectors / MAX_MSI_IRQS_PER_CTRL;
> @@ -86,14 +87,14 @@ irqreturn_t dw_handle_msi_irq(struct pcie_port *pp)
>         for (i = 0; i < num_ctrls; i++) {
>                 dw_pcie_rd_own_conf(pp, PCIE_MSI_INTR0_STATUS +
>                                         (i * MSI_REG_CTRL_BLOCK_SIZE),
> -                                   4, &val);
> -               if (!val)
> +                                   4, &status);
> +               if (!status)
>                         continue;
>
>                 ret = IRQ_HANDLED;
> +               val = status;
>                 pos = 0;
> -               while ((pos = find_next_bit((unsigned long *) &val,
> -                                           MAX_MSI_IRQS_PER_CTRL,
> +               while ((pos = find_next_bit(&val, MAX_MSI_IRQS_PER_CTRL,
>                                             pos)) != MAX_MSI_IRQS_PER_CTRL) {
>                         irq = irq_find_mapping(pp->irq_domain,
>                                                (i * MAX_MSI_IRQS_PER_CTRL) +
> --
> 2.21.0
>