[RFC PATCH] ARM: uprobes need icache flush after xol write
Oleg Nesterov
oleg at redhat.com
Tue Apr 8 08:27:35 PDT 2014
Sorry, I din't read the whole thread yet...
On 04/08, Russell King - ARM Linux wrote:
> On Tue, Apr 08, 2014 at 09:05:49AM -0400, David Long wrote:
> > Unfortunately copy_to_user_page() also needs a pointer to a vma struct
> > so, while it presumably provides the model to follow, it can't simply be
> > dropped in.
>
> Well, isn't this code doing the same thing as ptrace? It seems to want
> to modify a page in userspace of another process to change instructions
> that are going to be executed. That's what ptrace does, and ptrace
> already copes with all the issues there.
Yes, but it does get_user_pages(&vma) and thus it knows vma.
> Given that we've already solved that problem, wouldn't it be a good idea
> if the tracing code would stop trying to reinvent broken solutions to
> problems we have already solved?
But uprobes can't do this. Of course, I am not saying this is impossible,
but it would be nice to avoid mmap_sem/find_vma/etc.
Almost nobody (iirc only sparc?) actually uses this "vma" arguments. And
at least the supported architectures do not (at least this is what I think
after the quick grep).
Perhaps we can rolerate the hack below?
Oleg.
--- x/kernel/events/uprobes.c
+++ x/kernel/events/uprobes.c
@@ -1295,10 +1295,10 @@ static unsigned long xol_get_insn_slot(s
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.
+ * The architectures we currently support do not really use vma.
*/
- flush_dcache_page(area->page);
+ flush_icache_user_range(NULL /* vma */, area->page,
+ xol_vaddr, sizeof(uprobe->arch.ixol));
return xol_vaddr;
}
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