The only safe way for non core/arch code to use follow_pfn() is
together with an mmu_notifier subscription. follow_pfn() is already
marked as _GPL and the kerneldoc explains this restriction.
This patch here enforces all this by adding a mmu_notifier argument
and verifying that it is registered for the correct mm_struct.
Motivated by discussions with Christoph Hellwig and Jason Gunthorpe.
Signed-off-by: Daniel Vetter <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Jason Gunthorpe <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: John Hubbard <[email protected]>
Cc: Jérôme Glisse <[email protected]>
Cc: Jan Kara <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Daniel Vetter <[email protected]>
---
include/linux/mm.h | 3 ++-
mm/memory.c | 39 ++++++++++++++++++++++++++-------------
mm/nommu.c | 23 ++++++++++++++++++-----
virt/kvm/kvm_main.c | 4 ++--
4 files changed, 48 insertions(+), 21 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index aa0087feab24..14453f366efd 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1651,6 +1651,7 @@ void unmap_vmas(struct mmu_gather *tlb, struct vm_area_struct *start_vma,
unsigned long start, unsigned long end);
struct mmu_notifier_range;
+struct mmu_notifier;
void free_pgd_range(struct mmu_gather *tlb, unsigned long addr,
unsigned long end, unsigned long floor, unsigned long ceiling);
@@ -1660,7 +1661,7 @@ int follow_pte_pmd(struct mm_struct *mm, unsigned long address,
struct mmu_notifier_range *range,
pte_t **ptepp, pmd_t **pmdpp, spinlock_t **ptlp);
int follow_pfn(struct vm_area_struct *vma, unsigned long address,
- unsigned long *pfn);
+ unsigned long *pfn, struct mmu_notifier *subscription);
int unsafe_follow_pfn(struct vm_area_struct *vma, unsigned long address,
unsigned long *pfn);
int follow_phys(struct vm_area_struct *vma, unsigned long address,
diff --git a/mm/memory.c b/mm/memory.c
index 0db0c5e233fd..51fc0507663a 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4789,11 +4789,30 @@ int follow_pte_pmd(struct mm_struct *mm, unsigned long address,
}
EXPORT_SYMBOL(follow_pte_pmd);
+static int __follow_pfn(struct vm_area_struct *vma, unsigned long address,
+ unsigned long *pfn)
+{
+ int ret = -EINVAL;
+ spinlock_t *ptl;
+ pte_t *ptep;
+
+ if (!(vma->vm_flags & (VM_IO | VM_PFNMAP)))
+ return ret;
+
+ ret = follow_pte(vma->vm_mm, address, &ptep, &ptl);
+ if (ret)
+ return ret;
+ *pfn = pte_pfn(*ptep);
+ pte_unmap_unlock(ptep, ptl);
+ return 0;
+}
+
/**
* follow_pfn - look up PFN at a user virtual address
* @vma: memory mapping
* @address: user virtual address
* @pfn: location to store found PFN
+ * @subscription: mmu_notifier subscription for the mm @vma is part of
*
* Only IO mappings and raw PFN mappings are allowed. Note that callers must
* ensure coherency with pte updates by using a &mmu_notifier to follow updates.
@@ -4805,21 +4824,15 @@ EXPORT_SYMBOL(follow_pte_pmd);
* Return: zero and the pfn at @pfn on success, -ve otherwise.
*/
int follow_pfn(struct vm_area_struct *vma, unsigned long address,
- unsigned long *pfn)
+ unsigned long *pfn, struct mmu_notifier *subscription)
{
- int ret = -EINVAL;
- spinlock_t *ptl;
- pte_t *ptep;
+ if (WARN_ON(!subscription->mm))
+ return -EINVAL;
- if (!(vma->vm_flags & (VM_IO | VM_PFNMAP)))
- return ret;
+ if (WARN_ON(subscription->mm != vma->vm_mm))
+ return -EINVAL;
- ret = follow_pte(vma->vm_mm, address, &ptep, &ptl);
- if (ret)
- return ret;
- *pfn = pte_pfn(*ptep);
- pte_unmap_unlock(ptep, ptl);
- return 0;
+ return __follow_pfn(vma, address, pfn);
}
EXPORT_SYMBOL_GPL(follow_pfn);
@@ -4844,7 +4857,7 @@ int unsafe_follow_pfn(struct vm_area_struct *vma, unsigned long address,
WARN_ONCE(1, "unsafe follow_pfn usage\n");
add_taint(TAINT_USER, LOCKDEP_STILL_OK);
- return follow_pfn(vma, address, pfn);
+ return __follow_pfn(vma, address, pfn);
}
EXPORT_SYMBOL(unsafe_follow_pfn);
diff --git a/mm/nommu.c b/mm/nommu.c
index 79fc98a6c94a..2a6b46fe1906 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -111,24 +111,37 @@ unsigned int kobjsize(const void *objp)
return page_size(page);
}
+static int __follow_pfn(struct vm_area_struct *vma, unsigned long address,
+ unsigned long *pfn)
+{
+ if (!(vma->vm_flags & (VM_IO | VM_PFNMAP)))
+ return -EINVAL;
+
+ *pfn = address >> PAGE_SHIFT;
+ return 0;
+}
+
/**
* follow_pfn - look up PFN at a user virtual address
* @vma: memory mapping
* @address: user virtual address
* @pfn: location to store found PFN
+ * @subscription: mmu_notifier subscription for the mm @vma is part of
*
* Only IO mappings and raw PFN mappings are allowed.
*
* Returns zero and the pfn at @pfn on success, -ve otherwise.
*/
int follow_pfn(struct vm_area_struct *vma, unsigned long address,
- unsigned long *pfn)
+ unsigned long *pfn, struct mmu_notifier *subscription)
{
- if (!(vma->vm_flags & (VM_IO | VM_PFNMAP)))
+ if (WARN_ON(!subscription->mm))
return -EINVAL;
- *pfn = address >> PAGE_SHIFT;
- return 0;
+ if (WARN_ON(subscription->mm != vma->vm_mm))
+ return -EINVAL;
+
+ return __follow_pfn(vma, address, pfn);
}
EXPORT_SYMBOL_GPL(follow_pfn);
@@ -153,7 +166,7 @@ int unsafe_follow_pfn(struct vm_area_struct *vma, unsigned long address,
WARN_ONCE(1, "unsafe follow_pfn usage\n");
add_taint(TAINT_USER, LOCKDEP_STILL_OK);
- return follow_pfn(vma, address, pfn);
+ return __follow_pfn(vma, address, pfn);
}
EXPORT_SYMBOL(unsafe_follow_pfn);
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 417f3d470c3e..6f6786524eff 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1891,7 +1891,7 @@ static int hva_to_pfn_remapped(struct kvm *kvm, struct vm_area_struct *vma,
unsigned long pfn;
int r;
- r = follow_pfn(vma, addr, &pfn);
+ r = follow_pfn(vma, addr, &pfn, &kvm->mmu_notifier);
if (r) {
/*
* get_user_pages fails for VM_IO and VM_PFNMAP vmas and does
@@ -1906,7 +1906,7 @@ static int hva_to_pfn_remapped(struct kvm *kvm, struct vm_area_struct *vma,
if (r)
return r;
- r = follow_pfn(vma, addr, &pfn);
+ r = follow_pfn(vma, addr, &pfn, &kvm->mmu_notifier);
if (r)
return r;
--
2.29.2
On Thu, Nov 19, 2020 at 03:41:46PM +0100, Daniel Vetter wrote:
> @@ -4805,21 +4824,15 @@ EXPORT_SYMBOL(follow_pte_pmd);
> * Return: zero and the pfn at @pfn on success, -ve otherwise.
> */
> int follow_pfn(struct vm_area_struct *vma, unsigned long address,
> - unsigned long *pfn)
> + unsigned long *pfn, struct mmu_notifier *subscription)
> {
> - int ret = -EINVAL;
> - spinlock_t *ptl;
> - pte_t *ptep;
> + if (WARN_ON(!subscription->mm))
> + return -EINVAL;
>
> + if (WARN_ON(subscription->mm != vma->vm_mm))
> + return -EINVAL;
These two things are redundant right? vma->vm_mm != NULL?
BTW, why do we even have this for nommu? If the only caller is kvm,
can you even compile kvm on nommu??
Jason
On Tue, Nov 24, 2020 at 03:28:14PM +0100, Daniel Vetter wrote:
> On Fri, Nov 20, 2020 at 02:30:29PM -0400, Jason Gunthorpe wrote:
> > On Thu, Nov 19, 2020 at 03:41:46PM +0100, Daniel Vetter wrote:
> > > @@ -4805,21 +4824,15 @@ EXPORT_SYMBOL(follow_pte_pmd);
> > > * Return: zero and the pfn at @pfn on success, -ve otherwise.
> > > */
> > > int follow_pfn(struct vm_area_struct *vma, unsigned long address,
> > > - unsigned long *pfn)
> > > + unsigned long *pfn, struct mmu_notifier *subscription)
> > > {
> > > - int ret = -EINVAL;
> > > - spinlock_t *ptl;
> > > - pte_t *ptep;
> > > + if (WARN_ON(!subscription->mm))
> > > + return -EINVAL;
> > >
> > > + if (WARN_ON(subscription->mm != vma->vm_mm))
> > > + return -EINVAL;
> >
> > These two things are redundant right? vma->vm_mm != NULL?
>
> Yup, will remove.
>
> > BTW, why do we even have this for nommu? If the only caller is kvm,
> > can you even compile kvm on nommu??
>
> Kinda makes sense, but I have no idea how to make sure with compile
> testing this is really the case. And I didn't see any hard evidence in
> Kconfig or Makefile that mmu notifiers requires CONFIG_MMU. So not sure
> what to do here.
It looks like only some arches have selectable CONFIG_MMU: arm,
m68k, microblaze, riscv, sh
If we look at arches that work with HAVE_KVM, I only see: arm64, mips,
powerpc, s390, x86
So my conclusion is there is no intersection between !MMU and HAVE_KVM?
> Should I just remove the nommu version of follow_pfn and see what happens?
> We can't remove it earlier since it's still used by other
> subsystems.
This is what I was thinking might work
Jason
On Fri, Nov 20, 2020 at 02:30:29PM -0400, Jason Gunthorpe wrote:
> On Thu, Nov 19, 2020 at 03:41:46PM +0100, Daniel Vetter wrote:
> > @@ -4805,21 +4824,15 @@ EXPORT_SYMBOL(follow_pte_pmd);
> > * Return: zero and the pfn at @pfn on success, -ve otherwise.
> > */
> > int follow_pfn(struct vm_area_struct *vma, unsigned long address,
> > - unsigned long *pfn)
> > + unsigned long *pfn, struct mmu_notifier *subscription)
> > {
> > - int ret = -EINVAL;
> > - spinlock_t *ptl;
> > - pte_t *ptep;
> > + if (WARN_ON(!subscription->mm))
> > + return -EINVAL;
> >
> > + if (WARN_ON(subscription->mm != vma->vm_mm))
> > + return -EINVAL;
>
> These two things are redundant right? vma->vm_mm != NULL?
Yup, will remove.
> BTW, why do we even have this for nommu? If the only caller is kvm,
> can you even compile kvm on nommu??
Kinda makes sense, but I have no idea how to make sure with compile
testing this is really the case. And I didn't see any hard evidence in
Kconfig or Makefile that mmu notifiers requires CONFIG_MMU. So not sure
what to do here.
Should I just remove the nommu version of follow_pfn and see what happens?
We can't remove it earlier since it's still used by other subsystems.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
On Wed, Nov 25, 2020 at 9:13 AM Jason Gunthorpe <[email protected]> wrote:
>
> On Tue, Nov 24, 2020 at 03:28:14PM +0100, Daniel Vetter wrote:
> > On Fri, Nov 20, 2020 at 02:30:29PM -0400, Jason Gunthorpe wrote:
> > > On Thu, Nov 19, 2020 at 03:41:46PM +0100, Daniel Vetter wrote:
> > > > @@ -4805,21 +4824,15 @@ EXPORT_SYMBOL(follow_pte_pmd);
> > > > * Return: zero and the pfn at @pfn on success, -ve otherwise.
> > > > */
> > > > int follow_pfn(struct vm_area_struct *vma, unsigned long address,
> > > > - unsigned long *pfn)
> > > > + unsigned long *pfn, struct mmu_notifier *subscription)
> > > > {
> > > > - int ret = -EINVAL;
> > > > - spinlock_t *ptl;
> > > > - pte_t *ptep;
> > > > + if (WARN_ON(!subscription->mm))
> > > > + return -EINVAL;
> > > >
> > > > + if (WARN_ON(subscription->mm != vma->vm_mm))
> > > > + return -EINVAL;
> > >
> > > These two things are redundant right? vma->vm_mm != NULL?
> >
> > Yup, will remove.
> >
> > > BTW, why do we even have this for nommu? If the only caller is kvm,
> > > can you even compile kvm on nommu??
> >
> > Kinda makes sense, but I have no idea how to make sure with compile
> > testing this is really the case. And I didn't see any hard evidence in
> > Kconfig or Makefile that mmu notifiers requires CONFIG_MMU. So not sure
> > what to do here.
>
> It looks like only some arches have selectable CONFIG_MMU: arm,
> m68k, microblaze, riscv, sh
>
> If we look at arches that work with HAVE_KVM, I only see: arm64, mips,
> powerpc, s390, x86
>
> So my conclusion is there is no intersection between !MMU and HAVE_KVM?
>
> > Should I just remove the nommu version of follow_pfn and see what happens?
> > We can't remove it earlier since it's still used by other
> > subsystems.
>
> This is what I was thinking might work
Makes sense, I'll do that for the next round.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch