Messages in this thread | | | Date | Thu, 22 Dec 2022 15:18:53 +0200 | From | Mathias Nyman <> | Subject | Re: [PATCH v2] usb: xhci: Check endpoint is valid before dereferencing it |
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On 22.12.2022 13.52, Ladislav Michl wrote: > On Thu, Dec 22, 2022 at 01:08:47PM +0200, Mathias Nyman wrote: >> On 22.12.2022 11.01, Ladislav Michl wrote: >>> On Thu, Dec 22, 2022 at 07:29:12AM +0000, Jimmy Hu wrote: >>>> When the host controller is not responding, all URBs queued to all >>>> endpoints need to be killed. This can cause a kernel panic if we >>>> dereference an invalid endpoint. >>>> >>>> Fix this by using xhci_get_virt_ep() helper to find the endpoint and >>>> checking if the endpoint is valid before dereferencing it. >>>> >>>> [233311.853271] xhci-hcd xhci-hcd.1.auto: xHCI host controller not responding, assume dead >>>> [233311.853393] Unable to handle kernel NULL pointer dereference at virtual address 00000000000000e8 >>>> >>>> [233311.853964] pc : xhci_hc_died+0x10c/0x270 >>>> [233311.853971] lr : xhci_hc_died+0x1ac/0x270 >>>> >>>> [233311.854077] Call trace: >>>> [233311.854085] xhci_hc_died+0x10c/0x270 >>>> [233311.854093] xhci_stop_endpoint_command_watchdog+0x100/0x1a4 >>>> [233311.854105] call_timer_fn+0x50/0x2d4 >>>> [233311.854112] expire_timers+0xac/0x2e4 >>>> [233311.854118] run_timer_softirq+0x300/0xabc >>>> [233311.854127] __do_softirq+0x148/0x528 >>>> [233311.854135] irq_exit+0x194/0x1a8 >>>> [233311.854143] __handle_domain_irq+0x164/0x1d0 >>>> [233311.854149] gic_handle_irq.22273+0x10c/0x188 >>>> [233311.854156] el1_irq+0xfc/0x1a8 >>>> [233311.854175] lpm_cpuidle_enter+0x25c/0x418 [msm_pm] >>>> [233311.854185] cpuidle_enter_state+0x1f0/0x764 >>>> [233311.854194] do_idle+0x594/0x6ac >>>> [233311.854201] cpu_startup_entry+0x7c/0x80 >>>> [233311.854209] secondary_start_kernel+0x170/0x198 >>>> >>>> Fixes: 50e8725e7c42 ("xhci: Refactor command watchdog and fix split string.") >>>> Cc: stable@vger.kernel.org >>>> Signed-off-by: Jimmy Hu <hhhuuu@google.com> >>>> --- >>>> drivers/usb/host/xhci-ring.c | 5 ++++- >>>> 1 file changed, 4 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c >>>> index ddc30037f9ce..f5b0e1ce22af 100644 >>>> --- a/drivers/usb/host/xhci-ring.c >>>> +++ b/drivers/usb/host/xhci-ring.c >>>> @@ -1169,7 +1169,10 @@ static void xhci_kill_endpoint_urbs(struct xhci_hcd *xhci, >>>> struct xhci_virt_ep *ep; >>>> struct xhci_ring *ring; >>>> - ep = &xhci->devs[slot_id]->eps[ep_index]; >>>> + ep = xhci_get_virt_ep(xhci, slot_id, ep_index); >>>> + if (!ep) >>>> + return; >>>> + >>> >>> xhci_get_virt_ep also adds check for slot_id == 0. It changes behaviour, >>> do we really want to skip that slot? Original code went from 0 to >>> MAX_HC_SLOTS-1. >>> >>> It seems to be off by one to me. Am I missing anything? >> >> slot_id 0 is always invalid, so this is a good change. > > I see. Now reading more carefully: > #define HCS_MAX_SLOTS(p) (((p) >> 0) & 0xff) > #define MAX_HC_SLOTS 256 > So the loop should go: > for (i = 1; i <= HCS_MAX_SLOTS(xhci->hcs_params1); i++)
yes
> >>> Also, what about passing ep directly to xhci_kill_endpoint_urbs >>> and do the check in xhci_hc_died? Not even compile tested: >> >> passing ep to a function named kill_endpoint_urbs() sound like the >> right thing to do, but as a generic change. >> >> I think its a good idea to first do a targeted fix for this null pointer >> issue that we can send to stable fist. > > Agree. But I still do not understand the root cause. There is a check > for NULL xhci->devs[i] already, so patch does not add much more, except > for test for slot_id == 0. And the eps array is just array of > struct xhci_virt_ep, not a pointers to them, so &xhci->devs[i]->eps[j] > should be always valid pointer. However struct xhci_ring in each eps > is allocated and not protected by any lock here. Is that correct?
I think root cause is that freeing xhci->devs[i] and including rings isn't protected by the lock, this happens in xhci_free_virt_device() called by xhci_free_dev(), which in turn may be called by usbcore at any time
So xhci->devs[i] might just suddenly disappear
Patch just checks more often if xhci->devs[i] is valid, between every endpoint. So the race between xhci_free_virt_device() and xhci_kill_endpoint_urbs() doesn't trigger null pointer deref as easily.
> >>> diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c >>> index ddc30037f9ce..5dac483c562a 100644 >>> --- a/drivers/usb/host/xhci-ring.c >>> +++ b/drivers/usb/host/xhci-ring.c >>> @@ -1162,14 +1162,12 @@ static void xhci_kill_ring_urbs(struct xhci_hcd *xhci, struct xhci_ring *ring) >>> } >>> static void xhci_kill_endpoint_urbs(struct xhci_hcd *xhci, >>> - int slot_id, int ep_index) >>> + struct xhci_virt_ep *ep) >>> { >>> struct xhci_td *cur_td; >>> struct xhci_td *tmp; >>> - struct xhci_virt_ep *ep; >>> struct xhci_ring *ring; >>> - ep = &xhci->devs[slot_id]->eps[ep_index]; >>> if ((ep->ep_state & EP_HAS_STREAMS) || >>> (ep->ep_state & EP_GETTING_NO_STREAMS)) { >>> int stream_id; >>> @@ -1180,18 +1178,12 @@ static void xhci_kill_endpoint_urbs(struct xhci_hcd *xhci, >>> if (!ring) >>> continue; >>> - xhci_dbg_trace(xhci, trace_xhci_dbg_cancel_urb, >>> - "Killing URBs for slot ID %u, ep index %u, stream %u", >>> - slot_id, ep_index, stream_id); >>> xhci_kill_ring_urbs(xhci, ring); >>> } >>> } else { >>> ring = ep->ring; >>> if (!ring) >>> return; >>> - xhci_dbg_trace(xhci, trace_xhci_dbg_cancel_urb, >>> - "Killing URBs for slot ID %u, ep index %u", >>> - slot_id, ep_index); >>> xhci_kill_ring_urbs(xhci, ring); >>> } >>> @@ -1217,6 +1209,7 @@ static void xhci_kill_endpoint_urbs(struct xhci_hcd *xhci, >>> void xhci_hc_died(struct xhci_hcd *xhci) >>> { >>> int i, j; >>> + struct xhci_virt_ep *ep; >>> if (xhci->xhc_state & XHCI_STATE_DYING) >>> return; >>> @@ -1227,11 +1220,14 @@ void xhci_hc_died(struct xhci_hcd *xhci) >>> xhci_cleanup_command_queue(xhci); >>> /* return any pending urbs, remove may be waiting for them */ >>> - for (i = 0; i <= HCS_MAX_SLOTS(xhci->hcs_params1); i++) { >>> + for (i = 0; i < HCS_MAX_SLOTS(xhci->hcs_params1); i++) { >>> if (!xhci->devs[i]) >>> continue; >>> - for (j = 0; j < 31; j++) >>> - xhci_kill_endpoint_urbs(xhci, i, j); >>> + for (j = 0; j < EP_CTX_PER_DEV; j++) { >>> + ep = &xhci->devs[i]->eps[j]; >>> + if (ep) >>> + xhci_kill_endpoint_urbs(xhci, ep); >>> + } >> >> This does loop a bit more than the existing code. >> With this change its always HCS_MAX_SLOTS * EP_CTX_PER_DEV. >> Previously best case was just HCS_MAX_SLOTS. > > No, that's just the same:
you're right, incorrectly read that your patch deleted the "if (!xhci->devs[i]) continue;" lines.
Thanks -Mathias
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