[PATCH v38 10/24] mm: Add vm_ops->mprotect()

[Jarkko Sakkinen]

From: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>

Add vm_ops()->mprotect() for additional constraints for a VMA.

Intel Software Guard eXtensions (SGX) will use this callback to add two
constraints:

1. Verify that the address range does not have holes: each page address
   must be filled with an enclave page.
2. Verify that VMA permissions won't surpass the permissions of any enclave
   page within the address range. Enclave cryptographically sealed
   permissions for each page address that set the upper limit for possible
   VMA permissions. Not respecting this can cause #GP's to be emitted.

Cc: linux-mm@xxxxxxxxx
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Acked-by: Jethro Beekman <jethro@xxxxxxxxxxxx>
Reviewed-by: Darren Kenny <darren.kenny@xxxxxxxxxx>
Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Co-developed-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
---
 include/linux/mm.h | 3 +++
 mm/mprotect.c      | 5 ++++-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 97c83773b6f0..717726fcace6 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -547,6 +547,9 @@ struct vm_operations_struct {
 	void (*close)(struct vm_area_struct * area);
 	int (*split)(struct vm_area_struct * area, unsigned long addr);
 	int (*mremap)(struct vm_area_struct * area);
+	int (*mprotect)(struct vm_area_struct *vma,
+			struct vm_area_struct **pprev, unsigned long start,
+			unsigned long end, unsigned long newflags);
 	vm_fault_t (*fault)(struct vm_fault *vmf);
 	vm_fault_t (*huge_fault)(struct vm_fault *vmf,
 			enum page_entry_size pe_size);
diff --git a/mm/mprotect.c b/mm/mprotect.c
index ce8b8a5eacbb..f170f3da8a4f 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -610,7 +610,10 @@ static int do_mprotect_pkey(unsigned long start, size_t len,
 		tmp = vma->vm_end;
 		if (tmp > end)
 			tmp = end;
-		error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
+		if (vma->vm_ops && vma->vm_ops->mprotect)
+			error = vma->vm_ops->mprotect(vma, &prev, nstart, tmp, newflags);
+		else
+			error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
 		if (error)
 			goto out;
 		nstart = tmp;
-- 
2.25.1