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

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Date:	Sat, 26 Apr 2008 21:07:07 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Venki Pallipadi <venkatesh.pallipadi@...el.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: [patch] x86, PAT: disable /dev/mem mmap RAM with PAT


* Venki Pallipadi <venkatesh.pallipadi@...el.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@...el.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@...el.com>
Signed-off-by: Ingo Molnar <mingo@...e.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;
 	}
--
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