Re: [PATCH] parisc: only make executable areas executable

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On Thu, 2011-04-14 at 15:53 -0500, James Bottomley wrote:
> Currently parisc has the whole kernel marked as RWX, meaning any
> kernel page at all is eligible to be executed.  This can cause a
> theoretical problem on systems with combined I/D TLB because the act
> of referencing a page causes a TLB insertion with an executable bit.
> This TLB entry may be used by the CPU as the basis for speculating the
> page into the I-Cache.  If this speculated page is subsequently used
> for a user process, there is the possibility we will get a stale
> I-cache line picked up as the binary executes.
> 
> As a point of good practise, only mark actual kernel text pages as
> executable.  The same has to be done for init_text pages, but they're
> converted to data pages (and the I-Cache flushed) when the init memory
> is released.

Just sent this off, then realised (or rather found out why gdb no longer
traces binaries) that special casing the gateway page means that it
isn't executable via the gateway page, so here's the correct patch

James

---

From: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
Subject: [PATCH] parisc: only make executable areas executable

Currently parisc has the whole kernel marked as RWX, meaning any
kernel page at all is eligible to be executed.  This can cause a
theoretical problem on systems with combined I/D TLB because the act
of referencing a page causes a TLB insertion with an executable bit.
This TLB entry may be used by the CPU as the basis for speculating the
page into the I-Cache.  If this speculated page is subsequently used
for a user process, there is the possibility we will get a stale
I-cache line picked up as the binary executes.

As a point of good practice, only mark actual kernel text pages as
executable.  The same has to be done for init_text pages, but they're
converted to data pages (and the I-Cache flushed) when the init memory
is released.

diff --git a/arch/parisc/include/asm/pgtable.h b/arch/parisc/include/asm/pgtable.h
index 5d7b8ce..22dadeb 100644
--- a/arch/parisc/include/asm/pgtable.h
+++ b/arch/parisc/include/asm/pgtable.h
@@ -177,7 +177,10 @@ struct vm_area_struct;
 
 #define _PAGE_TABLE	(_PAGE_PRESENT | _PAGE_READ | _PAGE_WRITE |  _PAGE_DIRTY | _PAGE_ACCESSED)
 #define _PAGE_CHG_MASK	(PAGE_MASK | _PAGE_ACCESSED | _PAGE_DIRTY)
-#define _PAGE_KERNEL	(_PAGE_PRESENT | _PAGE_EXEC | _PAGE_READ | _PAGE_WRITE | _PAGE_DIRTY | _PAGE_ACCESSED)
+#define _PAGE_KERNEL_RO	(_PAGE_PRESENT | _PAGE_READ | _PAGE_DIRTY | _PAGE_ACCESSED)
+#define _PAGE_KERNEL_EXEC	(_PAGE_KERNEL_RO | _PAGE_EXEC)
+#define _PAGE_KERNEL_RWX	(_PAGE_KERNEL_EXEC | _PAGE_WRITE)
+#define _PAGE_KERNEL		(_PAGE_KERNEL_RO | _PAGE_WRITE)
 
 /* The pgd/pmd contains a ptr (in phys addr space); since all pgds/pmds
  * are page-aligned, we don't care about the PAGE_OFFSET bits, except
@@ -208,7 +211,9 @@ struct vm_area_struct;
 #define PAGE_COPY       PAGE_EXECREAD
 #define PAGE_RWX        __pgprot(_PAGE_PRESENT | _PAGE_USER | _PAGE_READ | _PAGE_WRITE | _PAGE_EXEC |_PAGE_ACCESSED)
 #define PAGE_KERNEL	__pgprot(_PAGE_KERNEL)
-#define PAGE_KERNEL_RO	__pgprot(_PAGE_KERNEL & ~_PAGE_WRITE)
+#define PAGE_KERNEL_EXEC	__pgprot(_PAGE_KERNEL_EXEC)
+#define PAGE_KERNEL_RWX	__pgprot(_PAGE_KERNEL_RWX)
+#define PAGE_KERNEL_RO	__pgprot(_PAGE_KERNEL_RO)
 #define PAGE_KERNEL_UNC	__pgprot(_PAGE_KERNEL | _PAGE_NO_CACHE)
 #define PAGE_GATEWAY    __pgprot(_PAGE_PRESENT | _PAGE_USER | _PAGE_ACCESSED | _PAGE_GATEWAY| _PAGE_READ)
 
diff --git a/arch/parisc/kernel/entry.S b/arch/parisc/kernel/entry.S
index ead8d2a..6f05944 100644
--- a/arch/parisc/kernel/entry.S
+++ b/arch/parisc/kernel/entry.S
@@ -692,6 +692,9 @@ ENTRY(fault_vector_11)
 END(fault_vector_11)
 
 #endif
+	/* Fault vector is separately protected and *must* be on its own page */
+	.align		PAGE_SIZE
+ENTRY(end_fault_vector)
 
 	.import		handle_interruption,code
 	.import		do_cpu_irq_mask,code
diff --git a/arch/parisc/kernel/head.S b/arch/parisc/kernel/head.S
index 145c5e4..37aabd7 100644
--- a/arch/parisc/kernel/head.S
+++ b/arch/parisc/kernel/head.S
@@ -106,8 +106,9 @@ $bss_loop:
 #endif
 
 
-	/* Now initialize the PTEs themselves */
-	ldo		0+_PAGE_KERNEL(%r0),%r3 /* Hardwired 0 phys addr start */
+	/* Now initialize the PTEs themselves.  We use RWX for
+	 * everything ... it will get remapped correctly later */
+	ldo		0+_PAGE_KERNEL_RWX(%r0),%r3 /* Hardwired 0 phys addr start */
 	ldi		(1<<(KERNEL_INITIAL_ORDER-PAGE_SHIFT)),%r11 /* PFN count */
 	load32		PA(pg0),%r1
 
diff --git a/arch/parisc/kernel/module.c b/arch/parisc/kernel/module.c
index 6e81bb5..cedbbb8 100644
--- a/arch/parisc/kernel/module.c
+++ b/arch/parisc/kernel/module.c
@@ -61,8 +61,10 @@
 #include <linux/string.h>
 #include <linux/kernel.h>
 #include <linux/bug.h>
+#include <linux/mm.h>
 #include <linux/slab.h>
 
+#include <asm/pgtable.h>
 #include <asm/unwind.h>
 
 #if 0
@@ -214,7 +216,13 @@ void *module_alloc(unsigned long size)
 {
 	if (size == 0)
 		return NULL;
-	return vmalloc(size);
+	/* using RWX means less protection for modules, but it's
+	 * easier than trying to map the text, data, init_text and
+	 * init_data correctly */
+	return __vmalloc_node_range(size, 1, VMALLOC_START, VMALLOC_END,
+				    GFP_KERNEL | __GFP_HIGHMEM,
+				    PAGE_KERNEL_RWX, -1,
+				    __builtin_return_address(0));
 }
 
 #ifndef CONFIG_64BIT
diff --git a/arch/parisc/kernel/vmlinux.lds.S b/arch/parisc/kernel/vmlinux.lds.S
index 8f1e4ef..bf6a43a 100644
--- a/arch/parisc/kernel/vmlinux.lds.S
+++ b/arch/parisc/kernel/vmlinux.lds.S
@@ -134,6 +134,7 @@ SECTIONS
 	. = ALIGN(16384);
 	__init_begin = .;
 	INIT_TEXT_SECTION(16384)
+	. = ALIGN(PAGE_SIZE);
 	INIT_DATA_SECTION(16)
 	/* we have to discard exit text and such at runtime, not link time */
 	.exit.text :
diff --git a/arch/parisc/mm/init.c b/arch/parisc/mm/init.c
index b7ed8d7..7e6b465 100644
--- a/arch/parisc/mm/init.c
+++ b/arch/parisc/mm/init.c
@@ -369,24 +369,158 @@ static void __init setup_bootmem(void)
 	request_resource(&sysram_resources[0], &pdcdata_resource);
 }
 
+static void __init map_pages(unsigned long start_vaddr,
+			     unsigned long start_paddr, unsigned long size,
+			     pgprot_t pgprot, int force)
+{
+	pgd_t *pg_dir;
+	pmd_t *pmd;
+	pte_t *pg_table;
+	unsigned long end_paddr;
+	unsigned long start_pmd;
+	unsigned long start_pte;
+	unsigned long tmp1;
+	unsigned long tmp2;
+	unsigned long address;
+	unsigned long vaddr;
+	unsigned long ro_start;
+	unsigned long ro_end;
+	unsigned long fv_addr;
+	unsigned long gw_addr;
+	extern const unsigned long fault_vector_20;
+	extern void * const linux_gateway_page;
+
+	ro_start = __pa((unsigned long)_text);
+	ro_end   = __pa((unsigned long)&data_start);
+	fv_addr  = __pa((unsigned long)&fault_vector_20) & PAGE_MASK;
+	gw_addr  = __pa((unsigned long)&linux_gateway_page) & PAGE_MASK;
+
+	end_paddr = start_paddr + size;
+
+	pg_dir = pgd_offset_k(start_vaddr);
+
+#if PTRS_PER_PMD == 1
+	start_pmd = 0;
+#else
+	start_pmd = ((start_vaddr >> PMD_SHIFT) & (PTRS_PER_PMD - 1));
+#endif
+	start_pte = ((start_vaddr >> PAGE_SHIFT) & (PTRS_PER_PTE - 1));
+
+	address = start_paddr;
+	vaddr = start_vaddr;
+	while (address < end_paddr) {
+#if PTRS_PER_PMD == 1
+		pmd = (pmd_t *)__pa(pg_dir);
+#else
+		pmd = (pmd_t *)pgd_address(*pg_dir);
+
+		/*
+		 * pmd is physical at this point
+		 */
+
+		if (!pmd) {
+			pmd = (pmd_t *) alloc_bootmem_low_pages_node(NODE_DATA(0), PAGE_SIZE << PMD_ORDER);
+			pmd = (pmd_t *) __pa(pmd);
+		}
+
+		pgd_populate(NULL, pg_dir, __va(pmd));
+#endif
+		pg_dir++;
+
+		/* now change pmd to kernel virtual addresses */
+
+		pmd = (pmd_t *)__va(pmd) + start_pmd;
+		for (tmp1 = start_pmd; tmp1 < PTRS_PER_PMD; tmp1++, pmd++) {
+
+			/*
+			 * pg_table is physical at this point
+			 */
+
+			pg_table = (pte_t *)pmd_address(*pmd);
+			if (!pg_table) {
+				pg_table = (pte_t *)
+					alloc_bootmem_low_pages_node(NODE_DATA(0), PAGE_SIZE);
+				pg_table = (pte_t *) __pa(pg_table);
+			}
+
+			pmd_populate_kernel(NULL, pmd, __va(pg_table));
+
+			/* now change pg_table to kernel virtual addresses */
+
+			pg_table = (pte_t *) __va(pg_table) + start_pte;
+			for (tmp2 = start_pte; tmp2 < PTRS_PER_PTE; tmp2++, pg_table++) {
+				pte_t pte;
+
+				/*
+				 * Map the fault vector writable so we can
+				 * write the HPMC checksum.
+				 */
+				if (force)
+					pte =  __mk_pte(address, pgprot);
+				else if (core_kernel_text(vaddr) &&
+					 address != fv_addr)
+					pte = __mk_pte(address, PAGE_KERNEL_EXEC);
+				else
+#if defined(CONFIG_PARISC_PAGE_SIZE_4KB)
+				if (address >= ro_start && address < ro_end
+							&& address != fv_addr
+							&& address != gw_addr)
+					pte = __mk_pte(address, PAGE_KERNEL_RO);
+				else
+#endif
+					pte = __mk_pte(address, pgprot);
+
+				if (address >= end_paddr) {
+					if (force)
+						break;
+					else
+						pte_val(pte) = 0;
+				}
+
+				set_pte(pg_table, pte);
+
+				address += PAGE_SIZE;
+				vaddr += PAGE_SIZE;
+			}
+			start_pte = 0;
+
+			if (address >= end_paddr)
+			    break;
+		}
+		start_pmd = 0;
+	}
+}
+
 void free_initmem(void)
 {
 	unsigned long addr;
 	unsigned long init_begin = (unsigned long)__init_begin;
 	unsigned long init_end = (unsigned long)__init_end;
 
-#ifdef CONFIG_DEBUG_KERNEL
+	/* The init text pages are marked R-X.  We have to
+	 * flush the icache and mark them RW-
+	 *
+	 * This is tricky, because map_pages is in the init section.
+	 * Do a dummy remap of the data section first (the data
+	 * section is already PAGE_KERNEL) to pull in the TLB entries
+	 * for map_kernel */
+	map_pages(init_begin, __pa(init_begin), init_end - init_begin,
+		  PAGE_KERNEL_RWX, 1);
+	/* now remap at PAGE_KERNEL since the TLB is pre-primed to execute
+	 * map_pages */
+	map_pages(init_begin, __pa(init_begin), init_end - init_begin,
+		  PAGE_KERNEL, 1);
+
+	/* force the kernel to see the new TLB entries */
+	__flush_tlb_range(0, init_begin, init_end);
 	/* Attempt to catch anyone trying to execute code here
 	 * by filling the page with BRK insns.
 	 */
 	memset((void *)init_begin, 0x00, init_end - init_begin);
+	/* finally dump all the instructions which were cached, since the
+	 * pages are no-longer executable */
 	flush_icache_range(init_begin, init_end);
-#endif
 	
-	/* align __init_begin and __init_end to page size,
-	   ignoring linker script where we might have tried to save RAM */
-	init_begin = PAGE_ALIGN(init_begin);
-	init_end = PAGE_ALIGN(init_end);
 	for (addr = init_begin; addr < init_end; addr += PAGE_SIZE) {
 		ClearPageReserved(virt_to_page(addr));
 		init_page_count(virt_to_page(addr));
@@ -616,114 +750,6 @@ void show_mem(unsigned int filter)
 #endif
 }
 
-
-static void __init map_pages(unsigned long start_vaddr, unsigned long start_paddr, unsigned long size, pgprot_t pgprot)
-{
-	pgd_t *pg_dir;
-	pmd_t *pmd;
-	pte_t *pg_table;
-	unsigned long end_paddr;
-	unsigned long start_pmd;
-	unsigned long start_pte;
-	unsigned long tmp1;
-	unsigned long tmp2;
-	unsigned long address;
-	unsigned long ro_start;
-	unsigned long ro_end;
-	unsigned long fv_addr;
-	unsigned long gw_addr;
-	extern const unsigned long fault_vector_20;
-	extern void * const linux_gateway_page;
-
-	ro_start = __pa((unsigned long)_text);
-	ro_end   = __pa((unsigned long)&data_start);
-	fv_addr  = __pa((unsigned long)&fault_vector_20) & PAGE_MASK;
-	gw_addr  = __pa((unsigned long)&linux_gateway_page) & PAGE_MASK;
-
-	end_paddr = start_paddr + size;
-
-	pg_dir = pgd_offset_k(start_vaddr);
-
-#if PTRS_PER_PMD == 1
-	start_pmd = 0;
-#else
-	start_pmd = ((start_vaddr >> PMD_SHIFT) & (PTRS_PER_PMD - 1));
-#endif
-	start_pte = ((start_vaddr >> PAGE_SHIFT) & (PTRS_PER_PTE - 1));
-
-	address = start_paddr;
-	while (address < end_paddr) {
-#if PTRS_PER_PMD == 1
-		pmd = (pmd_t *)__pa(pg_dir);
-#else
-		pmd = (pmd_t *)pgd_address(*pg_dir);
-
-		/*
-		 * pmd is physical at this point
-		 */
-
-		if (!pmd) {
-			pmd = (pmd_t *) alloc_bootmem_low_pages_node(NODE_DATA(0),PAGE_SIZE << PMD_ORDER);
-			pmd = (pmd_t *) __pa(pmd);
-		}
-
-		pgd_populate(NULL, pg_dir, __va(pmd));
-#endif
-		pg_dir++;
-
-		/* now change pmd to kernel virtual addresses */
-
-		pmd = (pmd_t *)__va(pmd) + start_pmd;
-		for (tmp1 = start_pmd; tmp1 < PTRS_PER_PMD; tmp1++,pmd++) {
-
-			/*
-			 * pg_table is physical at this point
-			 */
-
-			pg_table = (pte_t *)pmd_address(*pmd);
-			if (!pg_table) {
-				pg_table = (pte_t *)
-					alloc_bootmem_low_pages_node(NODE_DATA(0),PAGE_SIZE);
-				pg_table = (pte_t *) __pa(pg_table);
-			}
-
-			pmd_populate_kernel(NULL, pmd, __va(pg_table));
-
-			/* now change pg_table to kernel virtual addresses */
-
-			pg_table = (pte_t *) __va(pg_table) + start_pte;
-			for (tmp2 = start_pte; tmp2 < PTRS_PER_PTE; tmp2++,pg_table++) {
-				pte_t pte;
-
-				/*
-				 * Map the fault vector writable so we can
-				 * write the HPMC checksum.
-				 */
-#if defined(CONFIG_PARISC_PAGE_SIZE_4KB)
-				if (address >= ro_start && address < ro_end
-							&& address != fv_addr
-							&& address != gw_addr)
-				    pte = __mk_pte(address, PAGE_KERNEL_RO);
-				else
-#endif
-				    pte = __mk_pte(address, pgprot);
-
-				if (address >= end_paddr)
-					pte_val(pte) = 0;
-
-				set_pte(pg_table, pte);
-
-				address += PAGE_SIZE;
-			}
-			start_pte = 0;
-
-			if (address >= end_paddr)
-			    break;
-		}
-		start_pmd = 0;
-	}
-}
-
 /*
  * pagetable_init() sets up the page tables
  *
@@ -748,14 +774,14 @@ static void __init pagetable_init(void)
 		size = pmem_ranges[range].pages << PAGE_SHIFT;
 
 		map_pages((unsigned long)__va(start_paddr), start_paddr,
-			size, PAGE_KERNEL);
+			  size, PAGE_KERNEL, 0);
 	}
 
 #ifdef CONFIG_BLK_DEV_INITRD
 	if (initrd_end && initrd_end > mem_limit) {
 		printk(KERN_INFO "initrd: mapping %08lx-%08lx\n", initrd_start, initrd_end);
 		map_pages(initrd_start, __pa(initrd_start),
-			initrd_end - initrd_start, PAGE_KERNEL);
+			  initrd_end - initrd_start, PAGE_KERNEL, 0);
 	}
 #endif
 
@@ -780,7 +806,7 @@ static void __init gateway_init(void)
 	 */
 
 	map_pages(linux_gateway_page_addr, __pa(&linux_gateway_page),
-		PAGE_SIZE, PAGE_GATEWAY);
+		  PAGE_SIZE, PAGE_GATEWAY, 1);
 }
 
 #ifdef CONFIG_HPUX


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