x86/sgx: use vma_lookup() in sgx_encl_find()

Use vma_lookup() to find the VMA at a specific address.  As vma_lookup()
will return NULL if the address is not within any VMA, the start address
no longer needs to be validated.

Link: https://lkml.kernel.org/r/20210521174745.2219620-10-Liam.Howlett@Oracle.comSigned-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Reviewed-by: Laurent Dufour <ldufour@linux.ibm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/x86/kernel/cpu/sgx/encl.h

@@ -91,8 +91,8 @@ static inline int sgx_encl_find(struct mm_struct *mm, unsigned long addr,
 {
 	struct vm_area_struct *result;
 
-	result = find_vma(mm, addr);
-	if (!result || result->vm_ops != &sgx_vm_ops || addr < result->vm_start)
+	result = vma_lookup(mm, addr);
+	if (!result || result->vm_ops != &sgx_vm_ops)
 		return -EINVAL;
 
 	*vma = result;