linux-kernel - [PATCH 2/5] x86, mpx: do not set ->vm

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Date:	Mon, 13 Jul 2015 13:54:09 +0300
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Andy Lutomirski <luto@...capital.net>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH 2/5] x86, mpx: do not set ->vm_ops on mpx VMAs

MPX setups private anonymous mapping, but uses vma->vm_ops too.
This can confuse core VM, as it relies on vm->vm_ops to distinguish
file VMAs from anonymous.

As result we will get SIGBUS, because handle_pte_fault() thinks it's
file VMA without vm_ops->fault and it doesn't know how to handle the
situation properly.

Let's fix that by not setting ->vm_ops.

We don't really need ->vm_ops here: MPX VMA can be detected with VM_MPX
flag. And vma_merge() will not merge MPX VMA with non-MPX VMA, because
->vm_flags won't match.

The only thing left is name of VMA. I'm not sure if it's part of ABI, or
we can just drop it. The patch keep it by providing arch_vma_name() on x86.

Build tested only.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Thomas Gleixner <tglx@...utronix.de>
---
 arch/x86/mm/mmap.c |  7 +++++++
 arch/x86/mm/mpx.c  | 20 +-------------------
 2 files changed, 8 insertions(+), 19 deletions(-)

diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
index 9d518d693b4b..844b06d67df4 100644
--- a/arch/x86/mm/mmap.c
+++ b/arch/x86/mm/mmap.c
@@ -126,3 +126,10 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
 		mm->get_unmapped_area = arch_get_unmapped_area_topdown;
 	}
 }
+
+const char *arch_vma_name(struct vm_area_struct *vma)
+{
+	if (vma->vm_flags & VM_MPX)
+		return "[mpx]";
+	return NULL;
+}
diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c
index c439ec478216..4d1c11c07fe1 100644
--- a/arch/x86/mm/mpx.c
+++ b/arch/x86/mm/mpx.c
@@ -18,26 +18,9 @@
 #include <asm/processor.h>
 #include <asm/fpu-internal.h>
 
-static const char *mpx_mapping_name(struct vm_area_struct *vma)
-{
-	return "[mpx]";
-}
-
-static struct vm_operations_struct mpx_vma_ops = {
-	.name = mpx_mapping_name,
-};
-
-static int is_mpx_vma(struct vm_area_struct *vma)
-{
-	return (vma->vm_ops == &mpx_vma_ops);
-}
-
 /*
  * This is really a simplified "vm_mmap". it only handles MPX
  * bounds tables (the bounds directory is user-allocated).
- *
- * Later on, we use the vma->vm_ops to uniquely identify these
- * VMAs.
  */
 static unsigned long mpx_mmap(unsigned long len)
 {
@@ -83,7 +66,6 @@ static unsigned long mpx_mmap(unsigned long len)
 		ret = -ENOMEM;
 		goto out;
 	}
-	vma->vm_ops = &mpx_vma_ops;
 
 	if (vm_flags & VM_LOCKED) {
 		up_write(&mm->mmap_sem);
@@ -661,7 +643,7 @@ static int zap_bt_entries(struct mm_struct *mm,
 		 * so stop immediately and return an error.  This
 		 * probably results in a SIGSEGV.
 		 */
-		if (!is_mpx_vma(vma))
+		if (!(vma->vm_flags & VM_MPX))
 			return -EINVAL;
 
 		len = min(vma->vm_end, end) - addr;
-- 
2.1.4

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