[RFC PATCH] proc: clear_refs: do not clear reserved pages
will.deacon at arm.com
Sun Jan 15 10:07:07 EST 2012
Thanks for the explanation.
On Sat, Jan 14, 2012 at 05:36:37PM +0000, Hugh Dickins wrote:
> On Fri, 13 Jan 2012, Nicolas Pitre wrote:
> > Given Andrew's answer, this should be fine wrt Russell's concern.
> > Acked-by: Nicolas Pitre <nico at linaro.org>
> Yes, it should be okay as an urgent fix for -stable.
> But going forward, I doubt it's the right answer: comments below.
Ok great, getting this into -stable ASAP would be much appreciated. Can
somebody pick it up please?
> Please, going forward, can you delete your vectors page code, and
> use the gate_vma for it? Extending it a little if it somehow does
> not satsify your need. Or else can you please explain (ec706dab
> does not) why the gate_vma does not suit you.
> I'm not saying the horrible hack gate_vma mechanism is any safer
> than yours (the latest bug in it was fixed all of 13 days ago).
> But I am saying that one horrible hack is safer than two.
Something like what I've got below seems to do the trick, and clear_refs
also seems to behave when it's presented with the gate_vma. If Russell is
happy with the approach, we can move to the gate_vma in the future.
ARM: vectors: use gate_vma for vectors user mapping
The current user mapping for the vectors page is inserted as a `horrible
hack vma' into each task via arch_setup_additional_pages. This causes
problems with the MM subsystem and vm_normal_page, as described here:
Following the suggestion from Hugh in the above thread, this patch uses
the gate_vma for the vectors user mapping, therefore consolidating
the horrible hack VMAs into one.
Signed-off-by: Will Deacon <will.deacon at arm.com>
diff --git a/arch/arm/include/asm/elf.h b/arch/arm/include/asm/elf.h
index 0e9ce8d..38050b1 100644
@@ -130,8 +130,4 @@ struct mm_struct;
extern unsigned long arch_randomize_brk(struct mm_struct *mm);
#define arch_randomize_brk arch_randomize_brk
-extern int vectors_user_mapping(void);
-#define arch_setup_additional_pages(bprm, uses_interp) vectors_user_mapping()
diff --git a/arch/arm/include/asm/page.h b/arch/arm/include/asm/page.h
index ca94653..e851aa3 100644
@@ -151,6 +151,8 @@ extern void __cpu_copy_user_highpage(struct page *to, struct page *from,
#define clear_page(page) memset((void *)(page), 0, PAGE_SIZE)
extern void copy_page(void *to, const void *from);
+#define __HAVE_ARCH_GATE_AREA 1
#endif /* CONFIG_MMU */
diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index 3d0c6fb..c13b8f6 100644
@@ -493,22 +493,40 @@ unsigned long arch_randomize_brk(struct mm_struct *mm)
* The vectors page is always readable from user space for the
- * atomic helpers and the signal restart code. Let's declare a mapping
- * for it so it is visible through ptrace and /proc/<pid>/mem.
+ * atomic helpers and the signal restart code. Insert it into the
+ * gate_vma so that it is visible through ptrace and /proc/<pid>/mem.
+static struct vm_area_struct gate_vma;
+static int __init gate_vma_init(void)
- struct mm_struct *mm = current->mm;
- return install_special_mapping(mm, 0xffff0000, PAGE_SIZE,
- VM_READ | VM_EXEC |
- VM_MAYREAD | VM_MAYEXEC |
- VM_ALWAYSDUMP | VM_RESERVED,
+ gate_vma.vm_start = 0xffff0000;
+ gate_vma.vm_end = 0xffff0000 + PAGE_SIZE;
+ gate_vma.vm_page_prot = PAGE_READONLY_EXEC;
+ gate_vma.vm_flags = VM_READ | VM_EXEC |
+ VM_MAYREAD | VM_MAYEXEC |
+ return 0;
+struct vm_area_struct *get_gate_vma(struct mm_struct *mm)
+ return &gate_vma;
+int in_gate_area(struct mm_struct *mm, unsigned long addr)
+ return (addr >= gate_vma.vm_start) && (addr < gate_vma.vm_end);
+int in_gate_area_no_mm(unsigned long addr)
+ return in_gate_area(NULL, addr);
const char *arch_vma_name(struct vm_area_struct *vma)
- return (vma->vm_start == 0xffff0000) ? "[vectors]" : NULL;
+ return (vma == &gate_vma) ? "[vectors]" : NULL;
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