From: Jason Gunthorpe <jgg@xxxxxxxxxx> [ Upstream commit dcf40ed3a20d727be054c4a20db47b32cb5036d4 ] Let's try to have a consistent and clear strategy for error handling during domain attach failures. There are two broad categories, the first is callers doing destruction and trying to set the domain back to a previously good domain. These cases cannot handle failure during destruction flows and must succeed, or at least avoid a UAF on the current group->domain which is likely about to be freed. Many of the drivers are well behaved here and will not hit the WARN_ON's or a UAF, but some are doing hypercalls/etc that can fail unpredictably and don't meet the expectations. The second case is attaching a domain for the first time in a failable context, failure should restore the attachment back to group->domain using the above unfailable operation. Have __iommu_group_set_domain_internal() execute a common algorithm that tries to achieve this, and in the worst case, would leave a device "detached" or assigned to a global blocking domain. This relies on some existing common driver behaviors where attach failure will also do detatch and true IOMMU_DOMAIN_BLOCK implementations that are not allowed to ever fail. Name the first case with __iommu_group_set_domain_nofail() to make it clear. Pull all the error handling and WARN_ON generation into __iommu_group_set_domain_internal(). Avoid the obfuscating use of __iommu_group_for_each_dev() and be more careful about what should happen during failures by only touching devices we've already touched. Reviewed-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx> Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx> Tested-by: Heiko Stuebner <heiko@xxxxxxxxx> Tested-by: Niklas Schnelle <schnelle@xxxxxxxxxxxxx> Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx> Link: https://lore.kernel.org/r/3-v5-1b99ae392328+44574-iommu_err_unwind_jgg@xxxxxxxxxx Signed-off-by: Joerg Roedel <jroedel@xxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- drivers/iommu/iommu.c | 137 ++++++++++++++++++++++++++++++++++-------- 1 file changed, 112 insertions(+), 25 deletions(-) diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c index f1dcfa3f1a1b4..873e66ab1e2d7 100644 --- a/drivers/iommu/iommu.c +++ b/drivers/iommu/iommu.c @@ -97,8 +97,26 @@ static int __iommu_attach_device(struct iommu_domain *domain, struct device *dev); static int __iommu_attach_group(struct iommu_domain *domain, struct iommu_group *group); + +enum { + IOMMU_SET_DOMAIN_MUST_SUCCEED = 1 << 0, +}; + +static int __iommu_group_set_domain_internal(struct iommu_group *group, + struct iommu_domain *new_domain, + unsigned int flags); static int __iommu_group_set_domain(struct iommu_group *group, - struct iommu_domain *new_domain); + struct iommu_domain *new_domain) +{ + return __iommu_group_set_domain_internal(group, new_domain, 0); +} +static void __iommu_group_set_domain_nofail(struct iommu_group *group, + struct iommu_domain *new_domain) +{ + WARN_ON(__iommu_group_set_domain_internal( + group, new_domain, IOMMU_SET_DOMAIN_MUST_SUCCEED)); +} + static int iommu_create_device_direct_mappings(struct iommu_group *group, struct device *dev); static struct iommu_group *iommu_group_get_for_dev(struct device *dev); @@ -2028,15 +2046,13 @@ EXPORT_SYMBOL_GPL(iommu_domain_free); static void __iommu_group_set_core_domain(struct iommu_group *group) { struct iommu_domain *new_domain; - int ret; if (group->owner) new_domain = group->blocking_domain; else new_domain = group->default_domain; - ret = __iommu_group_set_domain(group, new_domain); - WARN(ret, "iommu driver failed to attach the default/blocking domain"); + __iommu_group_set_domain_nofail(group, new_domain); } static int __iommu_attach_device(struct iommu_domain *domain, @@ -2221,21 +2237,55 @@ int iommu_attach_group(struct iommu_domain *domain, struct iommu_group *group) } EXPORT_SYMBOL_GPL(iommu_attach_group); -static int iommu_group_do_set_platform_dma(struct device *dev, void *data) +static int __iommu_device_set_domain(struct iommu_group *group, + struct device *dev, + struct iommu_domain *new_domain, + unsigned int flags) { - const struct iommu_ops *ops = dev_iommu_ops(dev); - - if (!WARN_ON(!ops->set_platform_dma_ops)) - ops->set_platform_dma_ops(dev); + int ret; + ret = __iommu_attach_device(new_domain, dev); + if (ret) { + /* + * If we have a blocking domain then try to attach that in hopes + * of avoiding a UAF. Modern drivers should implement blocking + * domains as global statics that cannot fail. + */ + if ((flags & IOMMU_SET_DOMAIN_MUST_SUCCEED) && + group->blocking_domain && + group->blocking_domain != new_domain) + __iommu_attach_device(group->blocking_domain, dev); + return ret; + } return 0; } -static int __iommu_group_set_domain(struct iommu_group *group, - struct iommu_domain *new_domain) +/* + * If 0 is returned the group's domain is new_domain. If an error is returned + * then the group's domain will be set back to the existing domain unless + * IOMMU_SET_DOMAIN_MUST_SUCCEED, otherwise an error is returned and the group's + * domains is left inconsistent. This is a driver bug to fail attach with a + * previously good domain. We try to avoid a kernel UAF because of this. + * + * IOMMU groups are really the natural working unit of the IOMMU, but the IOMMU + * API works on domains and devices. Bridge that gap by iterating over the + * devices in a group. Ideally we'd have a single device which represents the + * requestor ID of the group, but we also allow IOMMU drivers to create policy + * defined minimum sets, where the physical hardware may be able to distiguish + * members, but we wish to group them at a higher level (ex. untrusted + * multi-function PCI devices). Thus we attach each device. + */ +static int __iommu_group_set_domain_internal(struct iommu_group *group, + struct iommu_domain *new_domain, + unsigned int flags) { + struct group_device *last_gdev; + struct group_device *gdev; + int result; int ret; + lockdep_assert_held(&group->mutex); + if (group->domain == new_domain) return 0; @@ -2245,8 +2295,12 @@ static int __iommu_group_set_domain(struct iommu_group *group, * platform specific behavior. */ if (!new_domain) { - __iommu_group_for_each_dev(group, NULL, - iommu_group_do_set_platform_dma); + for_each_group_device(group, gdev) { + const struct iommu_ops *ops = dev_iommu_ops(gdev->dev); + + if (!WARN_ON(!ops->set_platform_dma_ops)) + ops->set_platform_dma_ops(gdev->dev); + } group->domain = NULL; return 0; } @@ -2256,16 +2310,52 @@ static int __iommu_group_set_domain(struct iommu_group *group, * domain. This switch does not have to be atomic and DMA can be * discarded during the transition. DMA must only be able to access * either new_domain or group->domain, never something else. - * - * Note that this is called in error unwind paths, attaching to a - * domain that has already been attached cannot fail. */ - ret = __iommu_group_for_each_dev(group, new_domain, - iommu_group_do_attach_device); - if (ret) - return ret; + result = 0; + for_each_group_device(group, gdev) { + ret = __iommu_device_set_domain(group, gdev->dev, new_domain, + flags); + if (ret) { + result = ret; + /* + * Keep trying the other devices in the group. If a + * driver fails attach to an otherwise good domain, and + * does not support blocking domains, it should at least + * drop its reference on the current domain so we don't + * UAF. + */ + if (flags & IOMMU_SET_DOMAIN_MUST_SUCCEED) + continue; + goto err_revert; + } + } group->domain = new_domain; - return 0; + return result; + +err_revert: + /* + * This is called in error unwind paths. A well behaved driver should + * always allow us to attach to a domain that was already attached. + */ + last_gdev = gdev; + for_each_group_device(group, gdev) { + const struct iommu_ops *ops = dev_iommu_ops(gdev->dev); + + /* + * If set_platform_dma_ops is not present a NULL domain can + * happen only for first probe, in which case we leave + * group->domain as NULL and let release clean everything up. + */ + if (group->domain) + WARN_ON(__iommu_device_set_domain( + group, gdev->dev, group->domain, + IOMMU_SET_DOMAIN_MUST_SUCCEED)); + else if (ops->set_platform_dma_ops) + ops->set_platform_dma_ops(gdev->dev); + if (gdev == last_gdev) + break; + } + return ret; } void iommu_detach_group(struct iommu_domain *domain, struct iommu_group *group) @@ -3182,16 +3272,13 @@ EXPORT_SYMBOL_GPL(iommu_device_claim_dma_owner); static void __iommu_release_dma_ownership(struct iommu_group *group) { - int ret; - if (WARN_ON(!group->owner_cnt || !group->owner || !xa_empty(&group->pasid_array))) return; group->owner_cnt = 0; group->owner = NULL; - ret = __iommu_group_set_domain(group, group->default_domain); - WARN(ret, "iommu driver failed to attach the default domain"); + __iommu_group_set_domain_nofail(group, group->default_domain); } /** -- 2.39.2
