linux-kernel - [RFC v3 15/17] mm/spf: Add check on the VMA's flags

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Date:   Thu, 27 Apr 2017 17:52:54 +0200
From:   Laurent Dufour <ldufour@...ux.vnet.ibm.com>
To:     paulmck@...ux.vnet.ibm.com, peterz@...radead.org,
        akpm@...ux-foundation.org, kirill@...temov.name,
        ak@...ux.intel.com, mhocko@...nel.org, dave@...olabs.net,
        jack@...e.cz
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        haren@...ux.vnet.ibm.com, khandual@...ux.vnet.ibm.com,
        npiggin@...il.com, bsingharora@...il.com
Subject: [RFC v3 15/17] mm/spf: Add check on the VMA's flags

When handling speculative page fault we should check for the VMA's
access permission as it is done in handle_mm_fault() or access_error
in x86's fault handler.

Signed-off-by: Laurent Dufour <ldufour@...ux.vnet.ibm.com>
---
 mm/memory.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/mm/memory.c b/mm/memory.c
index 3b28de5838c7..4d9c6331ada1 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3756,6 +3756,30 @@ int handle_speculative_fault(struct mm_struct *mm, unsigned long address,
 	if (address < vma->vm_start || vma->vm_end <= address)
 		goto unlock;
 
+	/* XXX Could we handle huge page here ? */
+	if (unlikely(is_vm_hugetlb_page(vma)))
+		goto unlock;
+
+	/*
+	 * The three following checks are copied from access_error from
+	 * arch/x86/mm/fault.c
+	 * XXX they may not be applicable to all architectures
+	 */
+	if (!arch_vma_access_permitted(vma, flags & FAULT_FLAG_WRITE,
+				       flags & FAULT_FLAG_INSTRUCTION,
+				       flags & FAULT_FLAG_REMOTE))
+		goto unlock;
+
+	/* This is one is required to check that the VMA has write access set */
+	if (flags & FAULT_FLAG_WRITE) {
+		if (unlikely(!(vma->vm_flags & VM_WRITE)))
+			goto unlock;
+	} else {
+		/* XXX This may not be required */
+		if (unlikely(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE))))
+			goto unlock;
+	}
+
 	/*
 	 * We need to re-validate the VMA after checking the bounds, otherwise
 	 * we might have a false positive on the bounds.
-- 
2.7.4