[patch] x86, PAT: disable /dev/mem mmap RAM with PAT

Ingo Molnar
2008-04-26T19:07:29Z

* Venki Pallipadi <venkatesh.pallipadi@intel.com> wrote:

> OK. Below is the quick to disable /dev/mem mmap of RAM with PAT. This
> should go along with Ingo's patch that removes PAT dependency on
> NONPROMISC_DEVMEM. It makes things safer and eliminates aliasing.
> Still somewhat unclean as the range_is_allowed is duplicated. And
> also, just compile tested right now.

thanks, i've queued up the patch below. I'll do some testing and then
send it to Linus.

Ingo

--------------->
Subject: x86, PAT: disable /dev/mem mmap RAM with PAT
From: Venki Pallipadi <venkatesh.pallipadi@intel.com>
Date: Sat, 26 Apr 2008 11:32:12 -0700

disable /dev/mem mmap of RAM with PAT. It makes things safer and
eliminates aliasing. A future improvement would be to avoid the
range_is_allowed duplication.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
arch/x86/mm/pat.c | 31 +++++++++++++++++++++++++++++++
1 file changed, 31 insertions(+)

Index: linux-x86.q/arch/x86/mm/pat.c
===================================================================
--- linux-x86.q.orig/arch/x86/mm/pat.c
+++ linux-x86.q/arch/x86/mm/pat.c
@@ -16,6 +16,7 @@
#include <asm/msr.h>
#include <asm/tlbflush.h>
#include <asm/processor.h>
+#include <asm/page.h>
#include <asm/pgtable.h>
#include <asm/pat.h>
#include <asm/e820.h>
@@ -477,6 +478,33 @@ pgprot_t phys_mem_access_prot(struct fil
return vma_prot;
}

+#ifdef CONFIG_NONPROMISC_DEVMEM
+/* This check is done in drivers/char/mem.c in case of NONPROMISC_DEVMEM*/
+static inline int range_is_allowed(unsigned long pfn, unsigned long size)
+{
+ return 1;
+}
+#else
+static inline int range_is_allowed(unsigned long pfn, unsigned long size)
+{
+ u64 from = ((u64)pfn) << PAGE_SHIFT;
+ u64 to = from + size;
+ u64 cursor = from;
+
+ while (cursor < to) {
+ if (!devmem_is_allowed(pfn)) {
+ printk(KERN_INFO
+ "Program %s tried to access /dev/mem between %Lx->%Lx.\n",
+ current->comm, from, to);
+ return 0;
+ }
+ cursor += PAGE_SIZE;
+ pfn++;
+ }
+ return 1;
+}
+#endif /* CONFIG_NONPROMISC_DEVMEM */
+
int phys_mem_access_prot_allowed(struct file *file, unsigned long pfn,
unsigned long size, pgprot_t *vma_prot)
{
@@ -485,6 +513,9 @@ int phys_mem_access_prot_allowed(struct
unsigned long ret_flags;
int retval;

+ if (!range_is_allowed(pfn, size))
+ return 0;
+
if (file->f_flags & O_SYNC) {
flags = _PAGE_CACHE_UC;
}