Re: [PATCH 1/1] x86: fix text_poke

[Ingo Molnar <mingo@elte.hu>]

* Ingo Molnar <mingo@elte.hu> wrote:

> > > > The 0xf0 pattern comes from alternatives_smp_lock: text_poke(*ptr, 
> > > > ((unsigned char []){0xf0}), 1);
> > > 
> > > And we should really add a lot more sanity checking there.
> 
> something like the patch below? (untested)

the one below even builds and boots.

this assumes that all modules areas are allocated via PAGE_KERNEL_EXEC - 
but that is generally true on x86 due to NX. 32-bit uses vmalloc_exec(), 
64-bit uses __vmalloc_area(..., PAGE_KERNEL_EXEC).

Jiri ... if you have any desire/stamina to still test this code - does 
the patch below produce any warnings if you unapply your fix as well, 
during suspend/resume?

	Ingo

--------------->
Subject: x86: harden kernel code patching
From: Ingo Molnar <mingo@elte.hu>
Date: Fri Apr 25 17:07:03 CEST 2008

Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 arch/x86/kernel/alternative.c |    5 +++++
 mm/vmalloc.c                  |    3 +++
 2 files changed, 8 insertions(+)

Index: linux/arch/x86/kernel/alternative.c
===================================================================
--- linux.orig/arch/x86/kernel/alternative.c
+++ linux/arch/x86/kernel/alternative.c
@@ -518,6 +518,11 @@ void *__kprobes text_poke(void *addr, co
 	if (core_kernel_text((unsigned long)addr)) {
 		struct page *pages[2] = { virt_to_page(addr),
 			virt_to_page(addr + PAGE_SIZE) };
+		/*
+		 * Module text pages are PageReserved:
+		 */
+		WARN_ON(pages[0] && !PageReserved(pages[0]));
+		WARN_ON(pages[1] && !PageReserved(pages[1]));
 		if (!pages[1])
 			nr_pages = 1;
 		vaddr = vmap(pages, nr_pages, VM_MAP, PAGE_KERNEL);
Index: linux/mm/vmalloc.c
===================================================================
--- linux.orig/mm/vmalloc.c
+++ linux/mm/vmalloc.c
@@ -391,6 +391,7 @@ static void __vunmap(const void *addr, i
 			struct page *page = area->pages[i];
 
 			BUG_ON(!page);
+			ClearPageReserved(page);
 			__free_page(page);
 		}
 
@@ -507,6 +508,8 @@ static void *__vmalloc_area_node(struct 
 			area->nr_pages = i;
 			goto fail;
 		}
+		if (pgprot_val(prot) == pgprot_val(PAGE_KERNEL_EXEC))
+			SetPageReserved(page);
 		area->pages[i] = page;
 	}