Messages in this thread Patches in this message | | | Date | Thu, 15 Oct 2009 19:25:39 -0400 | Subject | [PATCH V6] x86: NX protection for kernel data | From | Siarhei Liakh <> |
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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 results of patch application may be observed in the diff of kernel page table dumps: --- 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 @@ -2,8 +2,9 @@ 0x00000000-0xc0000000 3G pmd ---[ Kernel Mapping ]--- 0xc0000000-0xc0100000 1M RW GLB x pte -0xc0100000-0xc048d000 3636K ro GLB x pte -0xc048d000-0xc0600000 1484K RW GLB x pte +0xc0100000-0xc0381000 2564K ro GLB x pte +0xc0381000-0xc048d000 1072K ro GLB NX pte +0xc048d000-0xc0600000 1484K RW GLB NX pte 0xc0600000-0xf7800000 882M RW PSE GLB NX pmd 0xf7800000-0xf79fe000 2040K RW GLB NX pte 0xf79fe000-0xf7a00000 8K pte
The patch have been developed for Linux 2.6.31-rc7 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 --- Signed-off-by: Siarhei Liakh <sliakh.lkml@gmail.com> Signed-off-by: Xuxian Jiang <jiang@cs.ncsu.edu> Acked-by: Arjan van de Ven <arjan@linux.intel.com>
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S index 78d185d..83ae734 100644 --- a/arch/x86/kernel/vmlinux.lds.S +++ b/arch/x86/kernel/vmlinux.lds.S @@ -43,14 +43,14 @@ 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 */ + user PT_LOAD FLAGS(6); /* RW_ */ + data.init PT_LOAD FLAGS(6); /* RW_ */ #ifdef CONFIG_SMP - percpu PT_LOAD FLAGS(7); /* RWE */ + percpu PT_LOAD FLAGS(6); /* RW_ */ #endif - data.init2 PT_LOAD FLAGS(7); /* RWE */ + data.init2 PT_LOAD FLAGS(6); /* RW_ */ #endif note PT_NOTE FLAGS(0); /* ___ */ } @@ -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..7bfd411 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 +441,29 @@ void free_init_pages(char *what, unsigned long begin, unsigned long end) #endif }
+void mark_nxdata_nx(void) +{ +#ifdef CONFIG_DEBUG_RODATA + /* + * When this called, init has already been executed and released, + * so everything past _etext sould be NX. + */ + unsigned long start = PAGE_ALIGN((unsigned long)(&_etext)); + unsigned long size = PAGE_ALIGN((unsigned long)(&_end)) - start; + + printk(KERN_INFO "NX-protecting the kernel data: %lx, %lu pages\n", + start, size >> PAGE_SHIFT); + set_memory_nx(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
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