performance i dont think we should be too worried about at this moment -
this code is so rarely used that it should be driven by robustness i
think.
one theoretical worry i have is that we've got the pending immediate
values changes from Mathieu. Those end up removing the original
BUG_ON(len > sizeof(long)) restriction (and the alignment check) and
uses a carefully crafted (but scary as hell) sequence of text_poke()
sequences to turn a marker into a single-instruction NOP when the marker
is inactive.
Single-instruction NOP markers is a rather ... tempting goal and it can
(and must be able to) patch instructions across page boundaries as well.
i think with the PageReserved WARN_ON() we should be sufficiently
protected against stray scribbles so Mathieu's fix might be usable as
well - see it below.
Note that the BUG_ON()s at the end of the text_poke() version below
should have caught this bug too i think - because the bug was due to
mis-mapping the pages due to the incorrect kernel_text_address()
condition so we'd have noticed that the expected bits did not end up in
the right place.
Ingo
----------------------->
Subject: Fix sched-devel text_poke
From: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Date: Thu, 24 Apr 2008 11:03:33 -0400
Use core_text_address() instead of kernel_text_address(). Deal with modules in
the same way used for the core kernel.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
arch/x86/kernel/alternative.c | 38 ++++++++++++++++++--------------------
1 file changed, 18 insertions(+), 20 deletions(-)
Index: linux/arch/x86/kernel/alternative.c
===================================================================
--- linux.orig/arch/x86/kernel/alternative.c
+++ linux/arch/x86/kernel/alternative.c
@@ -511,31 +511,29 @@ void *__kprobes text_poke(void *addr, co
unsigned long flags;
char *vaddr;
int nr_pages = 2;
+ struct page *pages[2];
+ int i;
- BUG_ON(len > sizeof(long));
- BUG_ON((((long)addr + len - 1) & ~(sizeof(long) - 1))
- - ((long)addr & ~(sizeof(long) - 1)));
- if (kernel_text_address((unsigned long)addr)) {
- struct page *pages[2] = { virt_to_page(addr),
- virt_to_page(addr + PAGE_SIZE) };
- if (!pages[1])
- nr_pages = 1;
- vaddr = vmap(pages, nr_pages, VM_MAP, PAGE_KERNEL);
- BUG_ON(!vaddr);
- local_irq_save(flags);
- memcpy(&vaddr[(unsigned long)addr & ~PAGE_MASK], opcode, len);
- local_irq_restore(flags);
- vunmap(vaddr);
+ if (!core_kernel_text((unsigned long)addr)) {
+ pages[0] = vmalloc_to_page(addr);
+ pages[1] = vmalloc_to_page(addr + PAGE_SIZE);
} else {
- /*
- * modules are in vmalloc'ed memory, always writable.
- */
- local_irq_save(flags);
- memcpy(addr, opcode, len);
- local_irq_restore(flags);
+ pages[0] = virt_to_page(addr);
+ pages[1] = virt_to_page(addr + PAGE_SIZE);
}
+ BUG_ON(!pages[0]);
+ if (!pages[1])
+ nr_pages = 1;
+ vaddr = vmap(pages, nr_pages, VM_MAP, PAGE_KERNEL);
+ BUG_ON(!vaddr);
+ local_irq_save(flags);
+ memcpy(&vaddr[(unsigned long)addr & ~PAGE_MASK], opcode, len);
+ local_irq_restore(flags);
+ vunmap(vaddr);
sync_core();
/* Could also do a CLFLUSH here to speed up CPU recovery; but
that causes hangs on some VIA CPUs. */
+ for (i = 0; i < len; i++)
+ BUG_ON(((char *)addr)[i] != ((char *)opcode)[i]);
return addr;
}
--
