[RFC PATCH] uprobes: copy to user-space xol page with proper cache flushing
David Long
dave.long at linaro.org
Tue Apr 15 10:19:27 PDT 2014
On 04/15/14 11:46, Oleg Nesterov wrote:
>
> But. Please do not add copy_to_user_page() into copy_to_page() (as your patch
> did). This is certainly not what uprobe_write_opcode() wants, we do not want
> or need "flush" in this case. The same for __create_xol_area().
>
It looked me like a call to a new __copy_to_user_page(current->mm, ...) in xol_get_insn_slot()
would be in line with David Miller's suggestion and would cure the problem on ARM (and hopefuly
be more philosophically correct for all architectures):
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 04709b6..b418626 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1287,6 +1287,7 @@ static unsigned long xol_get_insn_slot(struct uprobe *uprobe)
{
struct xol_area *area;
unsigned long xol_vaddr;
+ void *kaddr;
area = get_xol_area();
if (!area)
@@ -1297,13 +1298,11 @@ static unsigned long xol_get_insn_slot(struct uprobe *uprobe)
return 0;
/* Initialize the slot */
- copy_to_page(area->page, xol_vaddr,
- &uprobe->arch.ixol, sizeof(uprobe->arch.ixol));
- /*
- * We probably need flush_icache_user_range() but it needs vma.
- * This should work on supported architectures too.
- */
- flush_dcache_page(area->page);
+ kaddr = kmap_atomic(area->page);
+ __copy_to_user_page(current->mm, area->page, xol_vaddr,
+ kaddr + (xol_vaddr & ~PAGE_MASK),
+ &uprobe->arch.ixol, sizeof(uprobe->arch.ixol), true);
+ kunmap_atomic(kaddr);
return xol_vaddr;
}
Opinions? It's possible this approach isn't good enough. Cache operations and VM
are not my strong suit.
-dl
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