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    Subject[PATCH v2 1/4] PCI: s390: Fix use-after-free of PCI resources with per-function hotplug
    Date
    On s390 PCI functions may be hotplugged individually even when they
    belong to a multi-function device. In particular on an SR-IOV device VFs
    may be removed and later re-added.

    In commit a50297cf8235 ("s390/pci: separate zbus creation from
    scanning") it was missed however that struct pci_bus and struct
    zpci_bus's resource list retained a reference to the PCI functions MMIO
    resources even though those resources are released and freed on
    hot-unplug. These stale resources may subsequently be claimed when the
    PCI function re-appears resulting in use-after-free.

    One idea of fixing this use-after-free in s390 specific code that was
    investigated was to simply keep resources around from the moment a PCI
    function first appeared until the whole virtual PCI bus created for
    a multi-function device disappears. The problem with this however is
    that due to the requirement of artificial MMIO addreesses (address
    cookies) extra logic is then needed to keep the address cookies
    compatible on re-plug. At the same time the MMIO resources semantically
    belong to the PCI function so tying their lifecycle to the function
    seems more logical.

    Instead a simpler approach is to remove the resources of an individually
    hot-unplugged PCI function from the PCI bus's resource list while
    keeping the resources of other PCI functions on the PCI bus untouched.

    This is done by introducing pci_bus_remove_resource() to remove an
    individual resource. Similarly the resource also needs to be removed
    from the struct zpci_bus's resource list. It turns out however, that
    there is really no need to add the MMIO resources to the struct
    zpci_bus's resource list at all and instead we can simply use the
    zpci_bar_struct's resource pointer directly.

    Fixes: a50297cf8235 ("s390/pci: separate zbus creation from scanning")
    Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
    ---
    v1 -> v2:
    - Remove return at the end of function returning void

    arch/s390/pci/pci.c | 16 ++++++++++------
    arch/s390/pci/pci_bus.c | 12 +++++-------
    arch/s390/pci/pci_bus.h | 3 +--
    drivers/pci/bus.c | 21 +++++++++++++++++++++
    include/linux/pci.h | 1 +
    5 files changed, 38 insertions(+), 15 deletions(-)

    diff --git a/arch/s390/pci/pci.c b/arch/s390/pci/pci.c
    index ef38b1514c77..e16afacc8fd1 100644
    --- a/arch/s390/pci/pci.c
    +++ b/arch/s390/pci/pci.c
    @@ -544,8 +544,7 @@ static struct resource *__alloc_res(struct zpci_dev *zdev, unsigned long start,
    return r;
    }

    -int zpci_setup_bus_resources(struct zpci_dev *zdev,
    - struct list_head *resources)
    +int zpci_setup_bus_resources(struct zpci_dev *zdev)
    {
    unsigned long addr, size, flags;
    struct resource *res;
    @@ -581,7 +580,6 @@ int zpci_setup_bus_resources(struct zpci_dev *zdev,
    return -ENOMEM;
    }
    zdev->bars[i].res = res;
    - pci_add_resource(resources, res);
    }
    zdev->has_resources = 1;

    @@ -590,17 +588,23 @@ int zpci_setup_bus_resources(struct zpci_dev *zdev,

    static void zpci_cleanup_bus_resources(struct zpci_dev *zdev)
    {
    + struct resource *res;
    int i;

    + pci_lock_rescan_remove();
    for (i = 0; i < PCI_STD_NUM_BARS; i++) {
    - if (!zdev->bars[i].size || !zdev->bars[i].res)
    + res = zdev->bars[i].res;
    + if (!res)
    continue;

    + release_resource(res);
    + pci_bus_remove_resource(zdev->zbus->bus, res);
    zpci_free_iomap(zdev, zdev->bars[i].map_idx);
    - release_resource(zdev->bars[i].res);
    - kfree(zdev->bars[i].res);
    + zdev->bars[i].res = NULL;
    + kfree(res);
    }
    zdev->has_resources = 0;
    + pci_unlock_rescan_remove();
    }

    int pcibios_device_add(struct pci_dev *pdev)
    diff --git a/arch/s390/pci/pci_bus.c b/arch/s390/pci/pci_bus.c
    index 6a8da1b742ae..a99926af2b69 100644
    --- a/arch/s390/pci/pci_bus.c
    +++ b/arch/s390/pci/pci_bus.c
    @@ -41,9 +41,7 @@ static int zpci_nb_devices;
    */
    static int zpci_bus_prepare_device(struct zpci_dev *zdev)
    {
    - struct resource_entry *window, *n;
    - struct resource *res;
    - int rc;
    + int rc, i;

    if (!zdev_enabled(zdev)) {
    rc = zpci_enable_device(zdev);
    @@ -57,10 +55,10 @@ static int zpci_bus_prepare_device(struct zpci_dev *zdev)
    }

    if (!zdev->has_resources) {
    - zpci_setup_bus_resources(zdev, &zdev->zbus->resources);
    - resource_list_for_each_entry_safe(window, n, &zdev->zbus->resources) {
    - res = window->res;
    - pci_bus_add_resource(zdev->zbus->bus, res, 0);
    + zpci_setup_bus_resources(zdev);
    + for (i = 0; i < PCI_STD_NUM_BARS; i++) {
    + if (zdev->bars[i].res)
    + pci_bus_add_resource(zdev->zbus->bus, zdev->bars[i].res, 0);
    }
    }

    diff --git a/arch/s390/pci/pci_bus.h b/arch/s390/pci/pci_bus.h
    index e96c9860e064..af9f0ac79a1b 100644
    --- a/arch/s390/pci/pci_bus.h
    +++ b/arch/s390/pci/pci_bus.h
    @@ -30,8 +30,7 @@ static inline void zpci_zdev_get(struct zpci_dev *zdev)

    int zpci_alloc_domain(int domain);
    void zpci_free_domain(int domain);
    -int zpci_setup_bus_resources(struct zpci_dev *zdev,
    - struct list_head *resources);
    +int zpci_setup_bus_resources(struct zpci_dev *zdev);

    static inline struct zpci_dev *zdev_from_bus(struct pci_bus *bus,
    unsigned int devfn)
    diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
    index 83ae838ceb5f..549c4bd5caec 100644
    --- a/drivers/pci/bus.c
    +++ b/drivers/pci/bus.c
    @@ -76,6 +76,27 @@ struct resource *pci_bus_resource_n(const struct pci_bus *bus, int n)
    }
    EXPORT_SYMBOL_GPL(pci_bus_resource_n);

    +void pci_bus_remove_resource(struct pci_bus *bus, struct resource *res)
    +{
    + struct pci_bus_resource *bus_res, *tmp;
    + int i;
    +
    + for (i = 0; i < PCI_BRIDGE_RESOURCE_NUM; i++) {
    + if (bus->resource[i] == res) {
    + bus->resource[i] = NULL;
    + return;
    + }
    + }
    +
    + list_for_each_entry_safe(bus_res, tmp, &bus->resources, list) {
    + if (bus_res->res == res) {
    + list_del(&bus_res->list);
    + kfree(bus_res);
    + return;
    + }
    + }
    +}
    +
    void pci_bus_remove_resources(struct pci_bus *bus)
    {
    int i;
    diff --git a/include/linux/pci.h b/include/linux/pci.h
    index fafd8020c6d7..b50e5c79f7e3 100644
    --- a/include/linux/pci.h
    +++ b/include/linux/pci.h
    @@ -1438,6 +1438,7 @@ void pci_bus_add_resource(struct pci_bus *bus, struct resource *res,
    unsigned int flags);
    struct resource *pci_bus_resource_n(const struct pci_bus *bus, int n);
    void pci_bus_remove_resources(struct pci_bus *bus);
    +void pci_bus_remove_resource(struct pci_bus *bus, struct resource *res);
    int devm_request_pci_bus_resources(struct device *dev,
    struct list_head *resources);

    --
    2.37.2
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