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 boundary
2. Linker script is adjusted so .rodata and .data always start and
end on a page boundary
3. void mark_nxdata_nx(void) added to arch/x86/mm/init.c with actual
functionality: NX is set for all pages from _etext through _end.
4. mark_nxdata_nx() called from free_initmem() (after init has been released)
5. free_init_pages() sets released memory NX in arch/x86/mm/init.c
The patch have been developed for Linux 2.6.31-rc7 x86 by Siarhei Liakh
<[email protected]> and Xuxian Jiang <[email protected]>.
V1: initial patch for 2.6.30
V2: patch for 2.6.31-rc7
V3: moved all code into arch/x86, adjusted credits
---
Signed-off-by: Siarhei Liakh <[email protected]>
Signed-off-by: Xuxian Jiang <[email protected]>
diff --git a/CREDITS b/CREDITS
index 1a41bf4..a24b669 100644
--- a/CREDITS
+++ b/CREDITS
@@ -1657,6 +1657,13 @@ N: Niels Kristian Bech Jensen
E: [email protected]
D: Miscellaneous kernel updates and fixes.
+N: Xuxian Jiang
+E: [email protected]
+D: RO/NX protection for static kernel and LKMs
+S: North Carolina State University
+S: Raleigh, North Carolina
+S: USA
+
N: Michael K. Johnson
E: [email protected]
W: http://www.redhat.com/~johnsonm
@@ -2068,6 +2075,13 @@ S: Post Office Box 371
S: North Little Rock, Arkansas 72115
S: USA
+N: Siarhei Liakh
+E: [email protected]
+D: RO/NX protection for static kernel and LKMs
+S: North Carolina State University
+S: Raleigh, North Carolina
+S: USA
+
N: Stephan Linz
E: [email protected]
E: [email protected]
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 78d185d..1b036e3 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -43,7 +43,7 @@ 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(7); /* RWE */
data.init PT_LOAD FLAGS(7); /* RWE */
@@ -89,6 +89,8 @@ SECTIONS
IRQENTRY_TEXT
*(.fixup)
*(.gnu.warning)
+ /* .text should occupy whole number of pages */
+ . = ALIGN(PAGE_SIZE);
/* End of text section */
_etext = .;
} :text = 0x9090
@@ -151,6 +153,8 @@ SECTIONS
.data.read_mostly : AT(ADDR(.data.read_mostly) - LOAD_OFFSET) {
*(.data.read_mostly)
+ /* .data should occupy whole number of pages */
+ . = ALIGN(PAGE_SIZE);
/* End of data section */
_edata = .;
}
diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index 0607119..9091bc0 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -423,9 +423,10 @@ 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_rw(begin, (end - begin) >> PAGE_SHIFT);
+ set_memory_nx(begin, (end - begin) >> PAGE_SHIFT);
printk(KERN_INFO "Freeing %s: %luk freed\n", what, (end - begin) >> 10);
@@ -440,11 +441,31 @@ void free_init_pages(char *what, unsigned long
begin, unsigned long end)
#endif
}
+#ifndef CONFIG_DEBUG_RODATA
+static inline void mark_nxdata_nx(void) { }
+#else
+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);
+ unsigned long size = PFN_ALIGN(_end) - start;
+
+ printk(KERN_INFO "NX-protecting the kernel data: %lx, %lu pages\n",
+ start, size >> PAGE_SHIFT);
+ set_pages_nx(virt_to_page(start), size >> PAGE_SHIFT);
+}
+#endif
+
void free_initmem(void)
{
free_init_pages("unused kernel memory",
(unsigned long)(&__init_begin),
(unsigned long)(&__init_end));
+ /* Set kernel's data as NX */
+ mark_nxdata_nx();
}
#ifdef CONFIG_BLK_DEV_INITRD
* Siarhei Liakh <[email protected]> wrote:
> 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 boundary
> 2. Linker script is adjusted so .rodata and .data always start and
> end on a page boundary
> 3. void mark_nxdata_nx(void) added to arch/x86/mm/init.c with actual
> functionality: NX is set for all pages from _etext through _end.
> 4. mark_nxdata_nx() called from free_initmem() (after init has been released)
> 5. free_init_pages() sets released memory NX in arch/x86/mm/init.c
>
> The patch have been developed for Linux 2.6.31-rc7 x86 by Siarhei Liakh
> <[email protected]> and Xuxian Jiang <[email protected]>.
>
> V1: initial patch for 2.6.30
> V2: patch for 2.6.31-rc7
> V3: moved all code into arch/x86, adjusted credits
ok, i like it.
One small cleanliness detail before we can apply it to the x86 tree:
> --- a/arch/x86/mm/init.c
> +++ b/arch/x86/mm/init.c
> @@ -440,11 +441,31 @@ void free_init_pages(char *what, unsigned long
> begin, unsigned long end)
> #endif
> }
>
> +#ifndef CONFIG_DEBUG_RODATA
> +static inline void mark_nxdata_nx(void) { }
> +#else
> +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);
> + unsigned long size = PFN_ALIGN(_end) - start;
> +
> + printk(KERN_INFO "NX-protecting the kernel data: %lx, %lu pages\n",
> + start, size >> PAGE_SHIFT);
> + set_pages_nx(virt_to_page(start), size >> PAGE_SHIFT);
> +}
> +#endif
This #ifdef looks ugly, it starts with an #ifndef which is inverted
logic and mark_nxdata_nx() is a global symbol, needlessly. It should
be written as something like:
static void mark_nxdata_nx(void)
{
#ifdef CONFIG_DEBUG_RODATA
...
#endif
}
Thanks,
Ingo
On Fri, Sep 4, 2009 at 9:13 AM, Siarhei Liakh<[email protected]> wrote:
> 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 boundary
> 2. Linker script is adjusted so .rodata and .data always start and
> end on a page boundary
> 3. void mark_nxdata_nx(void) added to arch/x86/mm/init.c with actual
> functionality: NX is set for all pages from _etext through _end.
> 4. mark_nxdata_nx() called from free_initmem() (after init has been released)
> 5. free_init_pages() sets released memory NX in arch/x86/mm/init.c
>
> The patch have been developed for Linux 2.6.31-rc7 x86 by Siarhei Liakh
> <[email protected]> and Xuxian Jiang <[email protected]>.
>
> V1: initial patch for 2.6.30
> V2: patch for 2.6.31-rc7
> V3: moved all code into arch/x86, adjusted credits
Looks fine, but I don't think it is necessary to bother "CREDITS",
because now we have git. :)
Thanks.