x86: Add NX protection for kernel data

This patch expands functionality of CONFIG_DEBUG_RODATA to set main
(static) kernel data area as NX.

The following steps are taken to achieve this:

 1. Linker script is adjusted so .text always starts and ends on a page bound
 2. Linker script is adjusted so .rodata always start and end on a page boundary
 3. NX is set for all pages from _etext through _end in mark_rodata_ro.
 4. free_init_pages() sets released memory NX in arch/x86/mm/init.c
 5. bios rom is set to x when pcibios is used.

The results of patch application may be observed in the diff of kernel page
table dumps:

pcibios:

 -- data_nx_pt_before.txt       2009-10-13 07:48:59.000000000 -0400
 ++ data_nx_pt_after.txt        2009-10-13 07:26:46.000000000 -0400
  0x00000000-0xc0000000           3G                           pmd
  ---[ Kernel Mapping ]---
 -0xc0000000-0xc0100000           1M     RW             GLB x  pte
 +0xc0000000-0xc00a0000         640K     RW             GLB NX pte
 +0xc00a0000-0xc0100000         384K     RW             GLB x  pte
 -0xc0100000-0xc03d7000        2908K     ro             GLB x  pte
 +0xc0100000-0xc0318000        2144K     ro             GLB x  pte
 +0xc0318000-0xc03d7000         764K     ro             GLB NX pte
 -0xc03d7000-0xc0600000        2212K     RW             GLB x  pte
 +0xc03d7000-0xc0600000        2212K     RW             GLB NX pte
  0xc0600000-0xf7a00000         884M     RW         PSE GLB NX pmd
  0xf7a00000-0xf7bfe000        2040K     RW             GLB NX pte
  0xf7bfe000-0xf7c00000           8K                           pte

No pcibios:

 -- data_nx_pt_before.txt       2009-10-13 07:48:59.000000000 -0400
 ++ data_nx_pt_after.txt        2009-10-13 07:26:46.000000000 -0400
  0x00000000-0xc0000000           3G                           pmd
  ---[ Kernel Mapping ]---
 -0xc0000000-0xc0100000           1M     RW             GLB x  pte
 +0xc0000000-0xc0100000           1M     RW             GLB NX pte
 -0xc0100000-0xc03d7000        2908K     ro             GLB x  pte
 +0xc0100000-0xc0318000        2144K     ro             GLB x  pte
 +0xc0318000-0xc03d7000         764K     ro             GLB NX pte
 -0xc03d7000-0xc0600000        2212K     RW             GLB x  pte
 +0xc03d7000-0xc0600000        2212K     RW             GLB NX pte
  0xc0600000-0xf7a00000         884M     RW         PSE GLB NX pmd
  0xf7a00000-0xf7bfe000        2040K     RW             GLB NX pte
  0xf7bfe000-0xf7c00000           8K                           pte

The patch has been originally developed for Linux 2.6.34-rc2 x86 by
Siarhei Liakh <sliakh.lkml@gmail.com> and Xuxian Jiang <jiang@cs.ncsu.edu>.

 -v1:  initial patch for 2.6.30
 -v2:  patch for 2.6.31-rc7
 -v3:  moved all code into arch/x86, adjusted credits
 -v4:  fixed ifdef, removed credits from CREDITS
 -v5:  fixed an address calculation bug in mark_nxdata_nx()
 -v6:  added acked-by and PT dump diff to commit log
 -v7:  minor adjustments for -tip
 -v8:  rework with the merge of "Set first MB as RW+NX"

Signed-off-by: Siarhei Liakh <sliakh.lkml@gmail.com>
Signed-off-by: Xuxian Jiang <jiang@cs.ncsu.edu>
Signed-off-by: Matthieu CASTET <castet.matthieu@free.fr>
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: James Morris <jmorris@namei.org>
Cc: Andi Kleen <ak@muc.de>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Dave Jones <davej@redhat.com>
Cc: Kees Cook <kees.cook@canonical.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <4CE2F82E.60601@free.fr>
[ minor cleanliness edits ]
Signed-off-by: Ingo Molnar <mingo@elte.hu>

7 files changed, 57 insertions, 6 deletions

diff --git a/arch/x86/include/asm/pci.h b/arch/x86/include/asm/pci.h
index ca0437c714b2..676129229630 100644
--- a/arch/x86/include/asm/pci.h
+++ b/arch/x86/include/asm/pci.h
@@ -65,6 +65,7 @@ extern unsigned long pci_mem_start;
 
 #define PCIBIOS_MIN_CARDBUS_IO  0x4000
 
+extern int pcibios_enabled;
 void pcibios_config_init(void);
 struct pci_bus *pcibios_scan_root(int bus);
 
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index e03530aebfd0..bf4700755184 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -69,7 +69,7 @@ jiffies_64 = jiffies;
 
 PHDRS {
         text PT_LOAD FLAGS(5);          /* R_E */
-        data PT_LOAD FLAGS(7);          /* RWE */
+        data PT_LOAD FLAGS(6);          /* RW_ */
 #ifdef CONFIG_X86_64
         user PT_LOAD FLAGS(5);          /* R_E */
 #ifdef CONFIG_SMP
@@ -116,6 +116,10 @@ SECTIONS
 
         EXCEPTION_TABLE(16) :text = 0x9090
 
+#if defined(CONFIG_DEBUG_RODATA)
+        /* .text should occupy whole number of pages */
+        . = ALIGN(PAGE_SIZE);
+#endif
         X64_ALIGN_DEBUG_RODATA_BEGIN
         RO_DATA(PAGE_SIZE)
         X64_ALIGN_DEBUG_RODATA_END
@@ -335,7 +339,7 @@ SECTIONS
                 __bss_start = .;
                 *(.bss..page_aligned)
                 *(.bss)
-                . = ALIGN(4);
+                . = ALIGN(PAGE_SIZE);
                 __bss_stop = .;
         }
 
diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index c0e28a13de7d..947f42abe820 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -364,8 +364,9 @@ void free_init_pages(char *what, unsigned long begin, unsigned long end)
         /*
          * We just marked the kernel text read only above, now that
          * we are going to free part of that, we need to make that
-         * writeable first.
+         * writeable and non-executable first.
          */
+        set_memory_nx(begin, (end - begin) >> PAGE_SHIFT);
         set_memory_rw(begin, (end - begin) >> PAGE_SHIFT);
 
         printk(KERN_INFO "Freeing %s: %luk freed\n", what, (end - begin) >> 10);
diff --git a/arch/x86/mm/init_32.c b/arch/x86/mm/init_32.c
index 0e969f9f401b..f89b5bb4e93f 100644
--- a/arch/x86/mm/init_32.c
+++ b/arch/x86/mm/init_32.c
@@ -226,7 +226,7 @@ page_table_range_init(unsigned long start, unsigned long end, pgd_t *pgd_base)
 
 static inline int is_kernel_text(unsigned long addr)
 {
-        if (addr >= PAGE_OFFSET && addr <= (unsigned long)__init_end)
+        if (addr >= (unsigned long)_text && addr <= (unsigned long)__init_end)
                 return 1;
         return 0;
 }
@@ -912,6 +912,23 @@ void set_kernel_text_ro(void)
         set_pages_ro(virt_to_page(start), size >> PAGE_SHIFT);
 }
 
+static void mark_nxdata_nx(void)
+{
+        /*
+         * When this called, init has already been executed and released,
+         * so everything past _etext sould be NX.
+         */
+        unsigned long start = PFN_ALIGN(_etext);
+        /*
+         * This comes from is_kernel_text upper limit. Also HPAGE where used:
+         */
+        unsigned long size = (((unsigned long)__init_end + HPAGE_SIZE) & HPAGE_MASK) - start;
+
+        if (__supported_pte_mask & _PAGE_NX)
+                printk(KERN_INFO "NX-protecting the kernel data: %luk\n", size >> 10);
+        set_pages_nx(virt_to_page(start), size >> PAGE_SHIFT);
+}
+
 void mark_rodata_ro(void)
 {
         unsigned long start = PFN_ALIGN(_text);
@@ -946,6 +963,7 @@ void mark_rodata_ro(void)
         printk(KERN_INFO "Testing CPA: write protecting again\n");
         set_pages_ro(virt_to_page(start), size >> PAGE_SHIFT);
 #endif
+        mark_nxdata_nx();
 }
 #endif
 
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 71a59296af80..ce59c05cae12 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -788,6 +788,7 @@ void mark_rodata_ro(void)
         unsigned long rodata_start =
                 ((unsigned long)__start_rodata + PAGE_SIZE - 1) & PAGE_MASK;
         unsigned long end = (unsigned long) &__end_rodata_hpage_align;
+        unsigned long kernel_end = (((unsigned long)&__init_end + HPAGE_SIZE) & HPAGE_MASK);
         unsigned long text_end = PAGE_ALIGN((unsigned long) &__stop___ex_table);
         unsigned long rodata_end = PAGE_ALIGN((unsigned long) &__end_rodata);
         unsigned long data_start = (unsigned long) &_sdata;
@@ -802,7 +803,7 @@ void mark_rodata_ro(void)
          * The rodata section (but not the kernel text!) should also be
          * not-executable.
          */
-        set_memory_nx(rodata_start, (end - rodata_start) >> PAGE_SHIFT);
+        set_memory_nx(rodata_start, (kernel_end - rodata_start) >> PAGE_SHIFT);
 
         rodata_test();
 
diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 6f2a6b6deb6b..8b830ca14ac4 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -13,6 +13,7 @@
 #include <linux/pfn.h>
 #include <linux/percpu.h>
 #include <linux/gfp.h>
+#include <linux/pci.h>
 
 #include <asm/e820.h>
 #include <asm/processor.h>
@@ -261,8 +262,10 @@ static inline pgprot_t static_protections(pgprot_t prot, unsigned long address,
          * The BIOS area between 640k and 1Mb needs to be executable for
          * PCI BIOS based config access (CONFIG_PCI_GOBIOS) support.
          */
-        if (within(pfn, BIOS_BEGIN >> PAGE_SHIFT, BIOS_END >> PAGE_SHIFT))
+#ifdef CONFIG_PCI_BIOS
+        if (pcibios_enabled && within(pfn, BIOS_BEGIN >> PAGE_SHIFT, BIOS_END >> PAGE_SHIFT))
                 pgprot_val(forbidden) |= _PAGE_NX;
+#endif
 
         /*
          * The kernel text needs to be executable for obvious reasons
diff --git a/arch/x86/pci/pcbios.c b/arch/x86/pci/pcbios.c
index 2492d165096a..a5f7d0d63de0 100644
--- a/arch/x86/pci/pcbios.c
+++ b/arch/x86/pci/pcbios.c
@@ -9,6 +9,7 @@
 #include <linux/uaccess.h>
 #include <asm/pci_x86.h>
 #include <asm/pci-functions.h>
+#include <asm/cacheflush.h>
 
 /* BIOS32 signature: "_32_" */
 #define BIOS32_SIGNATURE        (('_' << 0) + ('3' << 8) + ('2' << 16) + ('_' << 24))
@@ -25,6 +26,27 @@
 #define PCIBIOS_HW_TYPE1_SPEC           0x10
 #define PCIBIOS_HW_TYPE2_SPEC           0x20
 
+int pcibios_enabled;
+
+/* According to the BIOS specification at:
+ * http://members.datafast.net.au/dft0802/specs/bios21.pdf, we could
+ * restrict the x zone to some pages and make it ro. But this may be
+ * broken on some bios, complex to handle with static_protections.
+ * We could make the 0xe0000-0x100000 range rox, but this can break
+ * some ISA mapping.
+ *
+ * So we let's an rw and x hole when pcibios is used. This shouldn't
+ * happen for modern system with mmconfig, and if you don't want it
+ * you could disable pcibios...
+ */
+static inline void set_bios_x(void)
+{
+        pcibios_enabled = 1;
+        set_memory_x(PAGE_OFFSET + BIOS_BEGIN, (BIOS_END - BIOS_BEGIN) >> PAGE_SHIFT);
+        if (__supported_pte_mask & _PAGE_NX)
+                printk(KERN_INFO "PCI : PCI BIOS aera is rw and x. Use pci=nobios if you want it NX.\n");
+}
+
 /*
  * This is the standard structure used to identify the entry point
  * to the BIOS32 Service Directory, as documented in
@@ -332,6 +354,7 @@ static struct pci_raw_ops * __devinit pci_find_bios(void)
                         DBG("PCI: BIOS32 Service Directory entry at 0x%lx\n",
                                         bios32_entry);
                         bios32_indirect.address = bios32_entry + PAGE_OFFSET;
+                        set_bios_x();
                         if (check_pcibios())
                                 return &pci_bios_access;
                 }