Re: [PATCH v13 08/35] KVM: Introduce KVM_SET_USER_MEMORY_REGION2
From: Sean Christopherson
Date: Mon Oct 30 2023 - 16:25:58 EST
On Mon, Oct 30, 2023, Paolo Bonzini wrote:
> On 10/27/23 20:21, Sean Christopherson wrote:
> >
> > + if (ioctl == KVM_SET_USER_MEMORY_REGION)
> > + size = sizeof(struct kvm_userspace_memory_region);
>
> This also needs a memset(&mem, 0, sizeof(mem)), otherwise the out-of-bounds
> access of the commit message becomes a kernel stack read.
Ouch. There's some irony. Might be worth doing memset(&mem, -1, sizeof(mem))
though as '0' is a valid file descriptor and a valid file offset.
> Probably worth adding a check on valid flags here.
Definitely needed. There's a very real bug here. But rather than duplicate flags
checking or plumb @ioctl all the way to __kvm_set_memory_region(), now that we
have the fancy guard(mutex) and there are no internal calls to kvm_set_memory_region(),
what if we:
1. Acquire/release slots_lock in __kvm_set_memory_region()
2. Call kvm_set_memory_region() from x86 code for the internal memslots
3. Disallow *any* flags for internal memslots
4. Open code check_memory_region_flags in kvm_vm_ioctl_set_memory_region()
5. Pass @ioctl to kvm_vm_ioctl_set_memory_region() and allow KVM_MEM_PRIVATE
only for KVM_SET_USER_MEMORY_REGION2
E.g. this over ~5 patches
---
arch/x86/kvm/x86.c | 2 +-
include/linux/kvm_host.h | 4 +--
virt/kvm/kvm_main.c | 65 +++++++++++++++++-----------------------
3 files changed, 29 insertions(+), 42 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e3eb608b6692..dd3e2017366c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -12478,7 +12478,7 @@ void __user * __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa,
m.guest_phys_addr = gpa;
m.userspace_addr = hva;
m.memory_size = size;
- r = __kvm_set_memory_region(kvm, &m);
+ r = kvm_set_memory_region(kvm, &m);
if (r < 0)
return ERR_PTR_USR(r);
}
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 687589ce9f63..fbb98efe8200 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1170,7 +1170,7 @@ static inline bool kvm_memslot_iter_is_valid(struct kvm_memslot_iter *iter, gfn_
* -- just change its flags
*
* Since flags can be changed by some of these operations, the following
- * differentiation is the best we can do for __kvm_set_memory_region():
+ * differentiation is the best we can do for __kvm_set_memory_region().
*/
enum kvm_mr_change {
KVM_MR_CREATE,
@@ -1181,8 +1181,6 @@ enum kvm_mr_change {
int kvm_set_memory_region(struct kvm *kvm,
const struct kvm_userspace_memory_region2 *mem);
-int __kvm_set_memory_region(struct kvm *kvm,
- const struct kvm_userspace_memory_region2 *mem);
void kvm_arch_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot);
void kvm_arch_memslots_updated(struct kvm *kvm, u64 gen);
int kvm_arch_prepare_memory_region(struct kvm *kvm,
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 23633984142f..39ceee2f67f2 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1608,28 +1608,6 @@ static void kvm_replace_memslot(struct kvm *kvm,
}
}
-static int check_memory_region_flags(struct kvm *kvm,
- const struct kvm_userspace_memory_region2 *mem)
-{
- u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;
-
- if (kvm_arch_has_private_mem(kvm))
- valid_flags |= KVM_MEM_PRIVATE;
-
- /* Dirty logging private memory is not currently supported. */
- if (mem->flags & KVM_MEM_PRIVATE)
- valid_flags &= ~KVM_MEM_LOG_DIRTY_PAGES;
-
-#ifdef __KVM_HAVE_READONLY_MEM
- valid_flags |= KVM_MEM_READONLY;
-#endif
-
- if (mem->flags & ~valid_flags)
- return -EINVAL;
-
- return 0;
-}
-
static void kvm_swap_active_memslots(struct kvm *kvm, int as_id)
{
struct kvm_memslots *slots = kvm_get_inactive_memslots(kvm, as_id);
@@ -2014,11 +1992,9 @@ static bool kvm_check_memslot_overlap(struct kvm_memslots *slots, int id,
* space.
*
* Discontiguous memory is allowed, mostly for framebuffers.
- *
- * Must be called holding kvm->slots_lock for write.
*/
-int __kvm_set_memory_region(struct kvm *kvm,
- const struct kvm_userspace_memory_region2 *mem)
+static int __kvm_set_memory_region(struct kvm *kvm,
+ const struct kvm_userspace_memory_region2 *mem)
{
struct kvm_memory_slot *old, *new;
struct kvm_memslots *slots;
@@ -2028,9 +2004,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
int as_id, id;
int r;
- r = check_memory_region_flags(kvm, mem);
- if (r)
- return r;
+ guard(mutex)(&kvm->slots_lock);
as_id = mem->slot >> 16;
id = (u16)mem->slot;
@@ -2139,27 +2113,42 @@ int __kvm_set_memory_region(struct kvm *kvm,
kfree(new);
return r;
}
-EXPORT_SYMBOL_GPL(__kvm_set_memory_region);
int kvm_set_memory_region(struct kvm *kvm,
const struct kvm_userspace_memory_region2 *mem)
{
- int r;
+ /* Flags aren't supported for KVM-internal memslots. */
+ if (WARN_ON_ONCE(mem->flags))
+ return -EINVAL;
- mutex_lock(&kvm->slots_lock);
- r = __kvm_set_memory_region(kvm, mem);
- mutex_unlock(&kvm->slots_lock);
- return r;
+ return __kvm_set_memory_region(kvm, mem);
}
EXPORT_SYMBOL_GPL(kvm_set_memory_region);
-static int kvm_vm_ioctl_set_memory_region(struct kvm *kvm,
+static int kvm_vm_ioctl_set_memory_region(struct kvm *kvm, unsigned int ioctl,
struct kvm_userspace_memory_region2 *mem)
{
+ u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;
+
+ if (ioctl == KVM_SET_USER_MEMORY_REGION2 &&
+ kvm_arch_has_private_mem(kvm))
+ valid_flags |= KVM_MEM_PRIVATE;
+
+ /* Dirty logging private memory is not currently supported. */
+ if (mem->flags & KVM_MEM_PRIVATE)
+ valid_flags &= ~KVM_MEM_LOG_DIRTY_PAGES;
+
+#ifdef __KVM_HAVE_READONLY_MEM
+ valid_flags |= KVM_MEM_READONLY;
+#endif
+
+ if (mem->flags & ~valid_flags)
+ return -EINVAL;
+
if ((u16)mem->slot >= KVM_USER_MEM_SLOTS)
return -EINVAL;
- return kvm_set_memory_region(kvm, mem);
+ return __kvm_set_memory_region(kvm, mem);
}
#ifndef CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT
@@ -5145,7 +5134,7 @@ static long kvm_vm_ioctl(struct file *filp,
if (copy_from_user(&mem, argp, size))
goto out;
- r = kvm_vm_ioctl_set_memory_region(kvm, &mem);
+ r = kvm_vm_ioctl_set_memory_region(kvm, ioctl, &mem);
break;
}
case KVM_GET_DIRTY_LOG: {
base-commit: 881375a408c0f4ea451ff14545b59216d2923881
--