On Thu, Jun 9, 2016 at 4:04 AM, Lukas Wunner <lukas@xxxxxxxxx> wrote:
> Subject: [PATCH] x86/quirks: Validate secondary bus number
>
> We used to brute-force scan buses 0 to 31 until commit 8659c406ade3
> ("x86: only scan the root bus in early PCI quirks") constrained the scan
> to the root bus, in part to shorten boot time.
>
> Commit 625a99d9bfd0 ("x86/quirks: Add early quirk to reset Apple AirPort
> card") reintroduced scanning of secondary buses, but used a recursive
> strategy to scan only buses that are actually present.
>
> However the secondary bus number read from a bridge's config space may
> be invalid, in particular a value of 0 causes an infinite loop. The PCI
> core goes beyond that and recurses to a child bus only if its bus number
> is greater than the parent bus number (see pci_scan_bridge()). Since the
> root bus is numbered 0, this implies that secondary buses may not be 0.
> Do the same on early scanning.
>
> Suggested-by: Yinghai Lu <yinghai@xxxxxxxxxx>
> Fixes: 625a99d9bfd0 ("x86/quirks: Add early quirk to reset Apple AirPort card")
> Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx>
> ---
> arch/x86/kernel/early-quirks.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/early-quirks.c b/arch/x86/kernel/early-quirks.c
> index 4e4e499..c24070e 100644
> --- a/arch/x86/kernel/early-quirks.c
> +++ b/arch/x86/kernel/early-quirks.c
> @@ -747,7 +747,8 @@ static int __init check_dev_quirk(int num, int slot, int func)
>
> if ((type & 0x7f) == PCI_HEADER_TYPE_BRIDGE) {
> sec = read_pci_config_byte(num, slot, func, PCI_SECONDARY_BUS);
> - early_pci_scan_bus(sec);
> + if (sec > num)
> + early_pci_scan_bus(sec);
> }
>
> if (!(type & 0x80))
If two bridges have sec, then early_pci_scan_bus still could be called
two times.
Maybe we can add one static array to recorded scanned bus.
static unsigned char scanned_bus[256];
and in early_pci_scan_bus check and set that before scanning.
Thanks
Yinghai
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