kernel/user: Allow user_struct::locked_vm to be usable for iommufd

Following the pattern of io_uring, perf, skb, and bpf, iommfd will use
user->locked_vm for accounting pinned pages. Ensure the value is included
in the struct and export free_uid() as iommufd is modular.

user->locked_vm is the good accounting to use for ulimit because it is
per-user, and the security sandboxing of locked pages is not supposed to
be per-process. Other places (vfio, vdpa and infiniband) have used
mm->pinned_vm and/or mm->locked_vm for accounting pinned pages, but this
is only per-process and inconsistent with the new FOLL_LONGTERM users in
the kernel.

Concurrent work is underway to try to put this in a cgroup, so everything
can be consistent and the kernel can provide a FOLL_LONGTERM limit that
actually provides security.

Link: https://lore.kernel.org/r/7-v6-a196d26f289e+11787-iommufd_jgg@nvidia.com
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Tested-by: Nicolin Chen <nicolinc@nvidia.com>
Tested-by: Yi Liu <yi.l.liu@intel.com>
Tested-by: Lixiao Yang <lixiao.yang@intel.com>
Tested-by: Matthew Rosato <mjrosato@linux.ibm.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

diff --git a/include/linux/sched/user.h b/include/linux/sched/user.h
index f054d0360a753340a2b1b818ae3f0a9645b5773b..4cc52698e214e2f709d314edce7a4e9a2e2f3d55 100644 (file)
--- a/include/linux/sched/user.h
+++ b/include/linux/sched/user.h
@@ -25,7 +25,7 @@ struct user_struct {
 
 #if defined(CONFIG_PERF_EVENTS) || defined(CONFIG_BPF_SYSCALL) || \
        defined(CONFIG_NET) || defined(CONFIG_IO_URING) || \
-       defined(CONFIG_VFIO_PCI_ZDEV_KVM)
+       defined(CONFIG_VFIO_PCI_ZDEV_KVM) || IS_ENABLED(CONFIG_IOMMUFD)
        atomic_long_t locked_vm;
 #endif
 #ifdef CONFIG_WATCH_QUEUE

diff --git a/kernel/user.c b/kernel/user.c
index e2cf8c22b539a7ecb8f48fd6b2a5d2cd5add7e41..d667debeafd6097221455acf6844413adc8e120f 100644 (file)
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -185,6 +185,7 @@ void free_uid(struct user_struct *up)
        if (refcount_dec_and_lock_irqsave(&up->__count, &uidhash_lock, &flags))
                free_user(up, flags);
 }
+EXPORT_SYMBOL_GPL(free_uid);
 
 struct user_struct *alloc_uid(kuid_t uid)
 {