Re: [PATCH] early: usb: xhci-dbc: Handle out of bounds xhci-xdbc capability

Hello,

Gentle ping for review feedback.

On 2026-07-20 19:12, Umang Jain via Kernel-dev wrote:
> Currently, the early xhci-dbc assumes that the extended capability
> can be mapped within the fixed boot time mappings dictated by
> NR_FIX_BTMAPS.
> 
> This patch iterates over the PCI BAR address size to find and map
> xhci-xdbc capability which could be out-of-bounds otherwise,
> in xdbc_map_pci_mmio(). The iterations map the maximum allowed
> boot time mappings (fixmap size) at a time and search for xhci-xdbc
> capability offset, till the end of the bar address size.
> 
> This brings the need to track the early_ioremap() mapped size separately
> hence, introduce additional struct member xhci_base_length in
> struct xdbc_state.
> 
> Signed-off-by: Umang Jain <[email protected]>
> ---
> Link to earlier RFC:
> https://lore.kernel.org/all/[email protected]/
> ---
>  drivers/usb/early/xhci-dbc.c | 94 +++++++++++++++++++++++++++++++++---
>  drivers/usb/early/xhci-dbc.h |  1 +
>  2 files changed, 87 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/usb/early/xhci-dbc.c b/drivers/usb/early/xhci-dbc.c
> index 41118bba9197..5e540b6bf962 100644
> --- a/drivers/usb/early/xhci-dbc.c
> +++ b/drivers/usb/early/xhci-dbc.c
> @@ -35,10 +35,23 @@ static bool early_console_keep;
>  static inline void xdbc_trace(const char *fmt, ...) { }
>  #endif /* XDBC_TRACE */
>  
> +/* Size of xHCI debug capability structure */
> +#define XDBC_MAPPING_SIZE	56
> +
> +enum xdbc_capability_flags {
> +	XDBC_CAP_FLAG_NONE		= 0,
> +	XDBC_CAP_FLAG_LEGACY		= 1 << 0,
> +	XDBC_CAP_FLAG_PROTOCOL		= 1 << 1,
> +	XDBC_CAP_FLAG_DEBUG		= 1 << 2,
> +};
> +
>  static void __iomem * __init xdbc_map_pci_mmio(u32 bus, u32 dev, u32 func)
>  {
> -	u64 val64, sz64, mask64;
> +	u64 val64, sz64, mask64, fixmap_size, mapped_size;
> +	enum xdbc_capability_flags cap_flags = XDBC_CAP_FLAG_NONE;
> +	bool found_all_caps = false;
>  	void __iomem *base;
> +	int offset;
>  	u32 val, sz;
>  	u8 byte;
>  
> @@ -85,7 +98,72 @@ static void __iomem * __init xdbc_map_pci_mmio(u32 bus, u32 dev, u32 func)
>  
>  	xdbc.xhci_start = val64;
>  	xdbc.xhci_length = sz64;
> -	base = early_ioremap(val64, sz64);
> +
> +	fixmap_size = NR_FIX_BTMAPS << PAGE_SHIFT;
> +	if (sz64 < fixmap_size) {
> +		xdbc.xhci_base_length = sz64;
> +		return early_ioremap(val64, sz64);
> +	}
> +
> +	/*
> +	 * Base address size is greater than fixed size boot mappings,
> +	 * hence iterate over the region one fixmap_size at a time,
> +	 * starting with XHCI_EXP_CAPS_DEBUG capability.
> +	 */
> +	base = early_ioremap(val64, fixmap_size);
> +	offset = xhci_find_next_ext_cap(base, 0, 0);
> +	mapped_size = fixmap_size;
> +
> +	while (mapped_size <= sz64) {
> +		val = readl(base + offset);
> +		switch (XHCI_EXT_CAPS_ID(val)) {
> +		case XHCI_EXT_CAPS_DEBUG:
> +			if (offset + XDBC_MAPPING_SIZE > fixmap_size) {
> +				early_iounmap(base, fixmap_size);
> +				base = early_ioremap(val64 + offset, XDBC_MAPPING_SIZE);
> +
> +				mapped_size += offset;
> +				cap_flags = XDBC_CAP_FLAG_NONE;
> +			}
> +			cap_flags |= XDBC_CAP_FLAG_DEBUG;
> +			break;
> +		case XHCI_EXT_CAPS_PROTOCOL:
> +			cap_flags |= XDBC_CAP_FLAG_PROTOCOL;
> +			break;
> +		case XHCI_EXT_CAPS_LEGACY:
> +			cap_flags |= XDBC_CAP_FLAG_LEGACY;
> +			break;
> +		}
> +
> +		if ((cap_flags & XDBC_CAP_FLAG_DEBUG) &&
> +		    (cap_flags & XDBC_CAP_FLAG_PROTOCOL) &&
> +		    (cap_flags & XDBC_CAP_FLAG_LEGACY)) {
> +			found_all_caps = true;
> +			break;
> +		}
> +
> +		/*
> +		 * Find offset to next xhci-ext capability, remap if the offset
> +		 * is out of bounds of the already mapped region.
> +		 */
> +		offset = xhci_find_next_ext_cap(base, offset, 0);
> +		if (!offset) {
> +			early_iounmap(base, fixmap_size);
> +			base = early_ioremap(val64 + mapped_size, fixmap_size);
> +			mapped_size += fixmap_size;
> +
> +			offset = xhci_find_next_ext_cap(base, 0, 0);
> +			cap_flags = XDBC_CAP_FLAG_NONE;
> +
> +		}
> +	}
> +
> +	if (found_all_caps) {
> +		xdbc.xhci_base_length = fixmap_size;
> +	} else {
> +		xdbc.xhci_base_length = 0;
> +		base = NULL;
> +	}
>  
>  	return base;
>  }
> @@ -643,9 +721,9 @@ int __init early_xdbc_parse_parameter(char *s, int keep_early)
>  	offset = xhci_find_next_ext_cap(xdbc.xhci_base, 0, XHCI_EXT_CAPS_DEBUG);
>  	if (!offset) {
>  		pr_notice("xhci host doesn't support debug capability\n");
> -		early_iounmap(xdbc.xhci_base, xdbc.xhci_length);
> +		early_iounmap(xdbc.xhci_base, xdbc.xhci_base_length);
>  		xdbc.xhci_base = NULL;
> -		xdbc.xhci_length = 0;
> +		xdbc.xhci_base_length = 0;
>  
>  		return -ENODEV;
>  	}
> @@ -682,9 +760,9 @@ int __init early_xdbc_setup_hardware(void)
>  		xdbc.table_base = NULL;
>  		xdbc.out_buf = NULL;
>  
> -		early_iounmap(xdbc.xhci_base, xdbc.xhci_length);
> +		early_iounmap(xdbc.xhci_base, xdbc.xhci_base_length);
>  		xdbc.xhci_base = NULL;
> -		xdbc.xhci_length = 0;
> +		xdbc.xhci_base_length = 0;
>  	}
>  
>  	return ret;
> @@ -987,7 +1065,7 @@ static int __init xdbc_init(void)
>  	}
>  
>  	raw_spin_lock_irqsave(&xdbc.lock, flags);
> -	early_iounmap(xdbc.xhci_base, xdbc.xhci_length);
> +	early_iounmap(xdbc.xhci_base, xdbc.xhci_base_length);
>  	xdbc.xhci_base = base;
>  	offset = xhci_find_next_ext_cap(xdbc.xhci_base, 0, XHCI_EXT_CAPS_DEBUG);
>  	xdbc.xdbc_reg = (struct xdbc_regs __iomem *)(xdbc.xhci_base + offset);
> @@ -1004,7 +1082,7 @@ static int __init xdbc_init(void)
>  	memblock_phys_free(xdbc.table_dma, PAGE_SIZE);
>  	memblock_phys_free(xdbc.out_dma, PAGE_SIZE);
>  	writel(0, &xdbc.xdbc_reg->control);
> -	early_iounmap(xdbc.xhci_base, xdbc.xhci_length);
> +	early_iounmap(xdbc.xhci_base, xdbc.xhci_base_length);
>  
>  	return ret;
>  }
> diff --git a/drivers/usb/early/xhci-dbc.h b/drivers/usb/early/xhci-dbc.h
> index 8b4d71de45fc..e2aefb796084 100644
> --- a/drivers/usb/early/xhci-dbc.h
> +++ b/drivers/usb/early/xhci-dbc.h
> @@ -144,6 +144,7 @@ struct xdbc_state {
>  	u32			dev;
>  	u32			func;
>  	void __iomem		*xhci_base;
> +	size_t			xhci_base_length;
>  	u64			xhci_start;
>  	size_t			xhci_length;
>  	int			port_number;