[kernel,v3,4/7] KVM: PPC: Account TCE-containing pages in locked_vm
diff mbox

Message ID 1455501309-47200-5-git-send-email-aik@ozlabs.ru
State Superseded
Headers show

Commit Message

Alexey Kardashevskiy Feb. 15, 2016, 1:55 a.m. UTC
At the moment pages used for TCE tables (in addition to pages addressed
by TCEs) are not counted in locked_vm counter so a malicious userspace
tool can call ioctl(KVM_CREATE_SPAPR_TCE) as many times as
RLIMIT_NOFILE and lock a lot of memory.

This adds counting for pages used for TCE tables.

This counts the number of pages required for a table plus pages for
the kvmppc_spapr_tce_table struct (TCE table descriptor) itself.

This changes release_spapr_tce_table() to store @npages on stack to
avoid calling kvmppc_stt_npages() in the loop (tiny optimization,
probably).

This does not change the amount of used memory.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
---
Changes:
v3:
* s/kvmppc_stt_npages/kvmppc_tce_pages/ as it returns the number of pages
occupied by TCE table
* added kvmppc_stt_pages() which returns total number of pages (TCE +
struct + all page*) to be accounted in locked_vm

v2:
* switched from long to unsigned long types
* added WARN_ON_ONCE() in locked_vm decrement case
---
 arch/powerpc/kvm/book3s_64_vio.c | 63 ++++++++++++++++++++++++++++++++++++----
 1 file changed, 58 insertions(+), 5 deletions(-)

Comments

David Gibson Feb. 15, 2016, 4:08 a.m. UTC | #1
On Mon, Feb 15, 2016 at 12:55:06PM +1100, Alexey Kardashevskiy wrote:
> At the moment pages used for TCE tables (in addition to pages addressed
> by TCEs) are not counted in locked_vm counter so a malicious userspace
> tool can call ioctl(KVM_CREATE_SPAPR_TCE) as many times as
> RLIMIT_NOFILE and lock a lot of memory.
> 
> This adds counting for pages used for TCE tables.
> 
> This counts the number of pages required for a table plus pages for
> the kvmppc_spapr_tce_table struct (TCE table descriptor) itself.
> 
> This changes release_spapr_tce_table() to store @npages on stack to
> avoid calling kvmppc_stt_npages() in the loop (tiny optimization,
> probably).
> 
> This does not change the amount of used memory.
> 
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

Alas, this may cause failures with older libvirts in certain
configurations which may not have estimated enough locked memory.
Newer libvirts should be taking this amount into account (even though
it wasn't actually accounted as locked vm until now).  Has to be done,
though.

Patch
diff mbox

diff --git a/arch/powerpc/kvm/book3s_64_vio.c b/arch/powerpc/kvm/book3s_64_vio.c
index 9526c34..1a1e14f 100644
--- a/arch/powerpc/kvm/book3s_64_vio.c
+++ b/arch/powerpc/kvm/book3s_64_vio.c
@@ -39,19 +39,65 @@ 
 
 #define TCES_PER_PAGE	(PAGE_SIZE / sizeof(u64))
 
-static long kvmppc_stt_npages(unsigned long window_size)
+static unsigned long kvmppc_tce_pages(unsigned long window_size)
 {
 	return ALIGN((window_size >> SPAPR_TCE_SHIFT)
 		     * sizeof(u64), PAGE_SIZE) / PAGE_SIZE;
 }
 
+static unsigned long kvmppc_stt_pages(unsigned long tce_pages)
+{
+	unsigned long stt_bytes = sizeof(struct kvmppc_spapr_tce_table) +
+			(tce_pages * sizeof(struct page *));
+
+	return tce_pages + ALIGN(stt_bytes, PAGE_SIZE) / PAGE_SIZE;
+}
+
+static long kvmppc_account_memlimit(unsigned long stt_pages, bool inc)
+{
+	long ret = 0;
+
+	if (!current || !current->mm)
+		return ret; /* process exited */
+
+	down_write(&current->mm->mmap_sem);
+
+	if (inc) {
+		unsigned long locked, lock_limit;
+
+		locked = current->mm->locked_vm + stt_pages;
+		lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
+		if (locked > lock_limit && !capable(CAP_IPC_LOCK))
+			ret = -ENOMEM;
+		else
+			current->mm->locked_vm += stt_pages;
+	} else {
+		if (WARN_ON_ONCE(stt_pages > current->mm->locked_vm))
+			stt_pages = current->mm->locked_vm;
+
+		current->mm->locked_vm -= stt_pages;
+	}
+
+	pr_debug("[%d] RLIMIT_MEMLOCK KVM %c%ld %ld/%ld%s\n", current->pid,
+			inc ? '+' : '-',
+			stt_pages << PAGE_SHIFT,
+			current->mm->locked_vm << PAGE_SHIFT,
+			rlimit(RLIMIT_MEMLOCK),
+			ret ? " - exceeded" : "");
+
+	up_write(&current->mm->mmap_sem);
+
+	return ret;
+}
+
 static void release_spapr_tce_table(struct rcu_head *head)
 {
 	struct kvmppc_spapr_tce_table *stt = container_of(head,
 			struct kvmppc_spapr_tce_table, rcu);
 	int i;
+	unsigned long npages = kvmppc_tce_pages(stt->window_size);
 
-	for (i = 0; i < kvmppc_stt_npages(stt->window_size); i++)
+	for (i = 0; i < npages; i++)
 		__free_page(stt->pages[i]);
 
 	kfree(stt);
@@ -62,7 +108,7 @@  static int kvm_spapr_tce_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 	struct kvmppc_spapr_tce_table *stt = vma->vm_file->private_data;
 	struct page *page;
 
-	if (vmf->pgoff >= kvmppc_stt_npages(stt->window_size))
+	if (vmf->pgoff >= kvmppc_tce_pages(stt->window_size))
 		return VM_FAULT_SIGBUS;
 
 	page = stt->pages[vmf->pgoff];
@@ -89,6 +135,8 @@  static int kvm_spapr_tce_release(struct inode *inode, struct file *filp)
 
 	kvm_put_kvm(stt->kvm);
 
+	kvmppc_account_memlimit(
+		kvmppc_stt_pages(kvmppc_tce_pages(stt->window_size)), false);
 	call_rcu(&stt->rcu, release_spapr_tce_table);
 
 	return 0;
@@ -103,7 +151,7 @@  long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,
 				   struct kvm_create_spapr_tce *args)
 {
 	struct kvmppc_spapr_tce_table *stt = NULL;
-	long npages;
+	unsigned long npages;
 	int ret = -ENOMEM;
 	int i;
 
@@ -113,7 +161,12 @@  long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,
 			return -EBUSY;
 	}
 
-	npages = kvmppc_stt_npages(args->window_size);
+	npages = kvmppc_tce_pages(args->window_size);
+	ret = kvmppc_account_memlimit(kvmppc_stt_pages(npages), true);
+	if (ret) {
+		stt = NULL;
+		goto fail;
+	}
 
 	stt = kzalloc(sizeof(*stt) + npages * sizeof(struct page *),
 		      GFP_KERNEL);