linux-kernel - Re: [PATCH] PCI: dwc: fix find_next

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Date:   Thu, 12 Sep 2019 14:04:30 +0100
From:   Andrew Murray <andrew.murray@....com>
To:     Niklas Cassel <niklas.cassel@...aro.org>
Cc:     Jingoo Han <jingoohan1@...il.com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI: dwc: fix find_next_bit() usage

On Wed, Sep 04, 2019 at 06:03:38PM +0200, Niklas Cassel 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@...aro.org>
> ---

Reviewed-by: Andrew Murray <andrew.murray@....com>

>  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
>