Re: [git pull] x86 PAT changes

Venki Pallipadi
2008-04-26T18:32:35Z

On Sat, Apr 26, 2008 at 10:15:33AM -0700, Linus Torvalds wrote:
>
>
> On Sat, 26 Apr 2008, Pallipadi, Venkatesh wrote:
> >
> > Agreed that NONPROMISC_DEVMEM is not really needed for read/write. But,
> > we will still need it for /dev/mem.
>
> If so, just disable it unconditionally for mmap.
>
> As mentioned, that's really just a return to original Linux /dev/mmap
> semantics: long ago (well, not _that_ long ago) we never used to be able
> to mmap() normal kernel memory, because the page counts would get screwed
> up on pages that weren't marked PG_Reserved.
>
> So the traditional Linux behavior for mmap() on /dev/mem was always to
> only allow it on memory that either had no "struct page *" backing at all,
> or that was marked PG_Reserved (ie the ISA hole ay 640k-1M and things like
> the BIOS tables etc).
>
> Going back to that doesn't sound horrible.
>

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.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>

---
arch/x86/mm/pat.c | 31 +++++++++++++++++++++++++++++++
1 file changed, 31 insertions(+)

Index: linux-2.6/arch/x86/mm/pat.c
===================================================================
--- linux-2.6.orig/arch/x86/mm/pat.c 2008-04-26 09:34:31.000000000 -0700
+++ linux-2.6/arch/x86/mm/pat.c 2008-04-26 11:25:57.000000000 -0700
@@ -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;
}