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Subject[PATCH 15/31] mm: factor out VMA fault permission checking
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From: Dave Hansen <dave.hansen@linux.intel.com>

This code matches a fault condition up with the VMA and ensures
that the VMA allows the fault to be handled instead of just
erroring out.

We will be extending this in a moment to comprehend protection
keys.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
---

b/mm/gup.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)

diff -puN mm/gup.c~pkeys-10-pte-fault mm/gup.c
--- a/mm/gup.c~pkeys-10-pte-fault 2016-01-28 15:52:22.856518359 -0800
+++ b/mm/gup.c 2016-01-28 15:52:22.860518543 -0800
@@ -611,6 +611,18 @@ next_page:
}
EXPORT_SYMBOL(__get_user_pages);

+bool vma_permits_fault(struct vm_area_struct *vma, unsigned int fault_flags)
+{
+ vm_flags_t vm_flags;
+
+ vm_flags = (fault_flags & FAULT_FLAG_WRITE) ? VM_WRITE : VM_READ;
+
+ if (!(vm_flags & vma->vm_flags))
+ return false;
+
+ return true;
+}
+
/*
* fixup_user_fault() - manually resolve a user page fault
* @tsk: the task_struct to use for page fault accounting, or
@@ -646,7 +658,6 @@ int fixup_user_fault(struct task_struct
bool *unlocked)
{
struct vm_area_struct *vma;
- vm_flags_t vm_flags;
int ret, major = 0;

if (unlocked)
@@ -657,8 +668,7 @@ retry:
if (!vma || address < vma->vm_start)
return -EFAULT;

- vm_flags = (fault_flags & FAULT_FLAG_WRITE) ? VM_WRITE : VM_READ;
- if (!(vm_flags & vma->vm_flags))
+ if (!vma_permits_fault(vma, fault_flags))
return -EFAULT;

ret = handle_mm_fault(mm, vma, address, fault_flags);
_
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