* David Hildenbrand [off-list ref] [210910 05:23]:

On 10.09.21 10:22, Niklas Schnelle wrote:

quoted

On Thu, 2021-09-09 at 16:59 +0200, David Hildenbrand wrote:

quoted

We should not walk/touch page tables outside of VMA boundaries when
holding only the mmap sem in read mode. Evil user space can modify the
VMA layout just before this function runs and e.g., trigger races with
page table removal code since commit dd2283f2605e ("mm: mmap: zap pages
with read mmap_sem in munmap").

find_vma() does not check if the address is >= the VMA start address;
use vma_lookup() instead.

Fixes: dd2283f2605e ("mm: mmap: zap pages with read mmap_sem in munmap")
Signed-off-by: David Hildenbrand <redacted>
---
  arch/s390/pci/pci_mmio.c | 4 ++--
  1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/s390/pci/pci_mmio.c b/arch/s390/pci/pci_mmio.c
index ae683aa623ac..c5b35ea129cf 100644
--- a/arch/s390/pci/pci_mmio.c
+++ b/arch/s390/pci/pci_mmio.c

@@ -159,7 +159,7 @@ SYSCALL_DEFINE3(s390_pci_mmio_write, unsigned long, mmio_addr,
  	mmap_read_lock(current->mm);
  	ret = -EINVAL;
-	vma = find_vma(current->mm, mmio_addr);
+	vma = vma_lookup(current->mm, mmio_addr);
  	if (!vma)
  		goto out_unlock_mmap;
  	if (!(vma->vm_flags & (VM_IO | VM_PFNMAP)))

@@ -298,7 +298,7 @@ SYSCALL_DEFINE3(s390_pci_mmio_read, unsigned long, mmio_addr,
  	mmap_read_lock(current->mm);
  	ret = -EINVAL;
-	vma = find_vma(current->mm, mmio_addr);
+	vma = vma_lookup(current->mm, mmio_addr);
  	if (!vma)
  		goto out_unlock_mmap;
  	if (!(vma->vm_flags & (VM_IO | VM_PFNMAP)))

Oh wow great find thanks! If I may say so these are not great function
names. Looking at the code vma_lookup() is inded find_vma() plus the
check that the looked up address is indeed inside the vma.

IIRC, vma_lookup() was introduced fairly recently. Before that, this
additional check was open coded (and still are in some instances). It's
confusing, I agree.

This confusion is why I introduced vma_lookup().  My hope is to reduce
the users of find_vma() to only those that actually need the added
functionality, which are mostly in the mm code.

quoted

I think this is pretty independent of the rest of the patches, so do
you want me to apply this patch independently or do you want to wait
for the others?

Sure, please go ahead and apply independently. It'd be great if you could
give it a quick sanity test, although I don't expect surprises --
unfortunately, the environment I have easily at hand is not very well suited
(#cpu, #mem, #disk ...) for anything that exceeds basic compile tests (and
even cross-compiling is significantly faster ...).

quoted

In any case:

Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>

Thanks!

-- 
Thanks,

David / dhildenb

Reviewed-by: Liam R. Howlett <redacted>