This patch ensures that there are no mixed (RW+X) pages mapped within first megabyte of kernel space (from PAGE_OFFSET up to beginning of .text). This is achieved through introduction of new compile-time option CONFIG_DEBUG_SET_1ST_MB_RWNX which controls how is_kernel_text() and static_protections() view the memory area in question. Special accommodations have been made for BIOS32/PCI BIOS services: according to BIOS32 specification (http://members.datafast.net.au/dft0802/specs/bios32.pdf), at most two pages per BIOS32 service should be set executable and no pages need to be writeable. This patch modifies bios32_service() to set proper page access permissions at time of service discovery, as described in the specification. Further, hardcoded protection of memory area between 640k to 1Mb have been removed from static_protections(), since only pages mentioned above need to be executable, not whole BIOS region. The net result of the patch application is as follows: ========== BEFORE ========== 0xc0000000-0xc0100000 1M RW GLB x pte 0xc0100000-0xc04b6000 3800K ro GLB x pte ... =========== AFTER =========== 0xc0000000-0xc00fb000 1004K RW GLB NX pte 0xc00fb000-0xc00fd000 8K ro GLB x pte 0xc00fd000-0xc0100000 12K RW GLB NX pte 0xc0100000-0xc04b6000 3800K ro GLB x pte ... Note that first MB is now RW+NX, except for 8K of RO+X used by BIOS32. The patch have been developed for Linux 2.6.33-rc5 x86 by Siarhei Liakh <sliakh.lkml@xxxxxxxxx> and Xuxian Jiang <jiang@xxxxxxxxxxx>. V1: original patch "Reducing footprint of BIOS32 service mappings" V2: Set first MB as RW+NX for linux 2.6.33-rc5 V3: minor adjustments for -tip V4: Replaced "1st" with "first" Signed-off-by: Siarhei Liakh <sliakh.lkml@xxxxxxxxx> Signed-off-by: Xuxian Jiang <jiang@xxxxxxxxxxx> --- diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug index 8b3c711..adeaa39 100644 --- a/arch/x86/Kconfig.debug +++ b/arch/x86/Kconfig.debug @@ -121,6 +121,17 @@ config DEBUG_NX_TEST and the software setup of this feature. If in doubt, say "N" +config DEBUG_SET_1ST_MB_RWNX + bool "Set first MB of kernel space mapping as RW+NX" + default n + depends on X86 + ---help--- + This option helps to catch unintended modifications/execution of + 1st megabyte of kernel address space. Such protection may interfere + with run-time code patching and legacy BIOS services residing within + the first MB of physical address space. + If in doubt, say "N". + config 4KSTACKS bool "Use 4Kb for kernel stacks instead of 8Kb" depends on X86_32 diff --git a/arch/x86/mm/init_32.c b/arch/x86/mm/init_32.c index bca7909..8fb9c3d 100644 --- a/arch/x86/mm/init_32.c +++ b/arch/x86/mm/init_32.c @@ -52,6 +52,12 @@ #include <asm/page_types.h> #include <asm/init.h> +#ifdef CONFIG_DEBUG_SET_1ST_MB_RWNX +#define TEXT_START _text +#else +#define TEXT_START PAGE_OFFSET +#endif + unsigned long highstart_pfn, highend_pfn; static noinline int do_test_wp_bit(void); @@ -225,7 +231,8 @@ 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_START + && addr <= (unsigned long)__init_end) return 1; return 0; } diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c index 532e793..93ac4e6 100644 --- a/arch/x86/mm/pageattr.c +++ b/arch/x86/mm/pageattr.c @@ -256,13 +256,14 @@ static inline pgprot_t static_protections(pgprot_t prot, unsigned long address, { pgprot_t forbidden = __pgprot(0); +#ifndef CONFIG_DEBUG_SET_1ST_MB_RWNX /* * 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)) pgprot_val(forbidden) |= _PAGE_NX; - +#endif /* * The kernel text needs to be executable for obvious reasons * Does not cover __inittext since that is gone later on. On diff --git a/arch/x86/pci/pcbios.c b/arch/x86/pci/pcbios.c index 2492d16..1102096 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)) @@ -59,6 +60,16 @@ static struct { unsigned short segment; } bios32_indirect = { 0, __KERNEL_CS }; +/* Set two consecutive pages as read-only and executable */ +void set_2_pages_rox(unsigned long addr) +{ +#ifdef CONFIG_DEBUG_SET_1ST_MB_RWNX + unsigned long pg_address = PFN_DOWN(addr + PAGE_OFFSET) << PAGE_SHIFT; + set_memory_ro(pg_address, 2); + set_memory_x(pg_address, 2); +#endif +} + /* * Returns the entry point for the given service, NULL on error */ @@ -83,15 +94,19 @@ static unsigned long bios32_service(unsigned long service) local_irq_restore(flags); switch (return_code) { - case 0: - return address + entry; - case 0x80: /* Not present */ - printk(KERN_WARNING "bios32_service(0x%lx): not present\n", service); - return 0; - default: /* Shouldn't happen */ - printk(KERN_WARNING "bios32_service(0x%lx): returned 0x%x -- BIOS bug!\n", - service, return_code); - return 0; + case 0: /* Service present, set proper page access */ + address += entry; + set_2_pages_rox(address); + return address; + case 0x80: /* Not present */ + printk(KERN_WARNING "bios32_service(0x%lx): not present\n", + service); + return 0; + default: /* Shouldn't happen */ + printk(KERN_WARNING "bios32_service(0x%lx): " + "returned 0x%x -- BIOS bug!\n", + service, return_code); + return 0; } } @@ -332,6 +347,7 @@ 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_2_pages_rox(bios32_entry); if (check_pcibios()) return &pci_bios_access; } -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
