kmemcheck: add the kmemcheck core

General description: kmemcheck is a patch to the linux kernel that
detects use of uninitialized memory. It does this by trapping every
read and write to memory that was allocated dynamically (e.g. using
kmalloc()). If a memory address is read that has not previously been
written to, a message is printed to the kernel log.

Thanks to Andi Kleen for the set_memory_4k() solution.

Andrew Morton suggested documenting the shadow member of struct page.

Signed-off-by: Vegard Nossum <vegardno@ifi.uio.no>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>

[export kmemcheck_mark_initialized]
[build fix for setup_max_cpus]
Signed-off-by: Ingo Molnar <mingo@elte.hu>

[rebased for mainline inclusion]
Signed-off-by: Vegard Nossum <vegardno@ifi.uio.no>

1 files changed, 650 insertions, 0 deletions

diff --git a/arch/x86/mm/kmemcheck/kmemcheck.c b/arch/x86/mm/kmemcheck/kmemcheck.c
new file mode 100644
index 000000000000..9de7d8f6b6e1
--- /dev/null
+++ b/arch/x86/mm/kmemcheck/kmemcheck.c
@@ -0,0 +1,650 @@
+/**
+ * kmemcheck - a heavyweight memory checker for the linux kernel
+ * Copyright (C) 2007, 2008  Vegard Nossum <vegardno@ifi.uio.no>
+ * (With a lot of help from Ingo Molnar and Pekka Enberg.)
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License (version 2) as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/kallsyms.h>
+#include <linux/kernel.h>
+#include <linux/kmemcheck.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/page-flags.h>
+#include <linux/percpu.h>
+#include <linux/ptrace.h>
+#include <linux/string.h>
+#include <linux/types.h>
+
+#include <asm/cacheflush.h>
+#include <asm/kmemcheck.h>
+#include <asm/pgtable.h>
+#include <asm/tlbflush.h>
+
+#include "error.h"
+#include "opcode.h"
+#include "pte.h"
+#include "shadow.h"
+
+#ifdef CONFIG_KMEMCHECK_DISABLED_BY_DEFAULT
+#  define KMEMCHECK_ENABLED 0
+#endif
+
+#ifdef CONFIG_KMEMCHECK_ENABLED_BY_DEFAULT
+#  define KMEMCHECK_ENABLED 1
+#endif
+
+#ifdef CONFIG_KMEMCHECK_ONESHOT_BY_DEFAULT
+#  define KMEMCHECK_ENABLED 2
+#endif
+
+int kmemcheck_enabled = KMEMCHECK_ENABLED;
+
+int __init kmemcheck_init(void)
+{
+	printk(KERN_INFO "kmemcheck: \"Bugs, beware!\"\n");
+
+#ifdef CONFIG_SMP
+	/*
+	 * Limit SMP to use a single CPU. We rely on the fact that this code
+	 * runs before SMP is set up.
+	 */
+	if (setup_max_cpus > 1) {
+		printk(KERN_INFO
+			"kmemcheck: Limiting number of CPUs to 1.\n");
+		setup_max_cpus = 1;
+	}
+#endif
+
+	return 0;
+}
+
+early_initcall(kmemcheck_init);
+
+#ifdef CONFIG_KMEMCHECK_DISABLED_BY_DEFAULT
+int kmemcheck_enabled = 0;
+#endif
+
+#ifdef CONFIG_KMEMCHECK_ENABLED_BY_DEFAULT
+int kmemcheck_enabled = 1;
+#endif
+
+#ifdef CONFIG_KMEMCHECK_ONESHOT_BY_DEFAULT
+int kmemcheck_enabled = 2;
+#endif
+
+/*
+ * We need to parse the kmemcheck= option before any memory is allocated.
+ */
+static int __init param_kmemcheck(char *str)
+{
+	if (!str)
+		return -EINVAL;
+
+	sscanf(str, "%d", &kmemcheck_enabled);
+	return 0;
+}
+
+early_param("kmemcheck", param_kmemcheck);
+
+int kmemcheck_show_addr(unsigned long address)
+{
+	pte_t *pte;
+
+	pte = kmemcheck_pte_lookup(address);
+	if (!pte)
+		return 0;
+
+	set_pte(pte, __pte(pte_val(*pte) | _PAGE_PRESENT));
+	__flush_tlb_one(address);
+	return 1;
+}
+
+int kmemcheck_hide_addr(unsigned long address)
+{
+	pte_t *pte;
+
+	pte = kmemcheck_pte_lookup(address);
+	if (!pte)
+		return 0;
+
+	set_pte(pte, __pte(pte_val(*pte) & ~_PAGE_PRESENT));
+	__flush_tlb_one(address);
+	return 1;
+}
+
+struct kmemcheck_context {
+	bool busy;
+	int balance;
+
+	/*
+	 * There can be at most two memory operands to an instruction, but
+	 * each address can cross a page boundary -- so we may need up to
+	 * four addresses that must be hidden/revealed for each fault.
+	 */
+	unsigned long addr[4];
+	unsigned long n_addrs;
+	unsigned long flags;
+
+	/* Data size of the instruction that caused a fault. */
+	unsigned int size;
+};
+
+static DEFINE_PER_CPU(struct kmemcheck_context, kmemcheck_context);
+
+bool kmemcheck_active(struct pt_regs *regs)
+{
+	struct kmemcheck_context *data = &__get_cpu_var(kmemcheck_context);
+
+	return data->balance > 0;
+}
+
+/* Save an address that needs to be shown/hidden */
+static void kmemcheck_save_addr(unsigned long addr)
+{
+	struct kmemcheck_context *data = &__get_cpu_var(kmemcheck_context);
+
+	BUG_ON(data->n_addrs >= ARRAY_SIZE(data->addr));
+	data->addr[data->n_addrs++] = addr;
+}
+
+static unsigned int kmemcheck_show_all(void)
+{
+	struct kmemcheck_context *data = &__get_cpu_var(kmemcheck_context);
+	unsigned int i;
+	unsigned int n;
+
+	n = 0;
+	for (i = 0; i < data->n_addrs; ++i)
+		n += kmemcheck_show_addr(data->addr[i]);
+
+	return n;
+}
+
+static unsigned int kmemcheck_hide_all(void)
+{
+	struct kmemcheck_context *data = &__get_cpu_var(kmemcheck_context);
+	unsigned int i;
+	unsigned int n;
+
+	n = 0;
+	for (i = 0; i < data->n_addrs; ++i)
+		n += kmemcheck_hide_addr(data->addr[i]);
+
+	return n;
+}
+
+/*
+ * Called from the #PF handler.
+ */
+void kmemcheck_show(struct pt_regs *regs)
+{
+	struct kmemcheck_context *data = &__get_cpu_var(kmemcheck_context);
+
+	BUG_ON(!irqs_disabled());
+
+	if (unlikely(data->balance != 0)) {
+		kmemcheck_show_all();
+		kmemcheck_error_save_bug(regs);
+		data->balance = 0;
+		return;
+	}
+
+	/*
+	 * None of the addresses actually belonged to kmemcheck. Note that
+	 * this is not an error.
+	 */
+	if (kmemcheck_show_all() == 0)
+		return;
+
+	++data->balance;
+
+	/*
+	 * The IF needs to be cleared as well, so that the faulting
+	 * instruction can run "uninterrupted". Otherwise, we might take
+	 * an interrupt and start executing that before we've had a chance
+	 * to hide the page again.
+	 *
+	 * NOTE: In the rare case of multiple faults, we must not override
+	 * the original flags:
+	 */
+	if (!(regs->flags & X86_EFLAGS_TF))
+		data->flags = regs->flags;
+
+	regs->flags |= X86_EFLAGS_TF;
+	regs->flags &= ~X86_EFLAGS_IF;
+}
+
+/*
+ * Called from the #DB handler.
+ */
+void kmemcheck_hide(struct pt_regs *regs)
+{
+	struct kmemcheck_context *data = &__get_cpu_var(kmemcheck_context);
+	int n;
+
+	BUG_ON(!irqs_disabled());
+
+	if (data->balance == 0)
+		return;
+
+	if (unlikely(data->balance != 1)) {
+		kmemcheck_show_all();
+		kmemcheck_error_save_bug(regs);
+		data->n_addrs = 0;
+		data->balance = 0;
+
+		if (!(data->flags & X86_EFLAGS_TF))
+			regs->flags &= ~X86_EFLAGS_TF;
+		if (data->flags & X86_EFLAGS_IF)
+			regs->flags |= X86_EFLAGS_IF;
+		return;
+	}
+
+	if (kmemcheck_enabled)
+		n = kmemcheck_hide_all();
+	else
+		n = kmemcheck_show_all();
+
+	if (n == 0)
+		return;
+
+	--data->balance;
+
+	data->n_addrs = 0;
+
+	if (!(data->flags & X86_EFLAGS_TF))
+		regs->flags &= ~X86_EFLAGS_TF;
+	if (data->flags & X86_EFLAGS_IF)
+		regs->flags |= X86_EFLAGS_IF;
+}
+
+void kmemcheck_show_pages(struct page *p, unsigned int n)
+{
+	unsigned int i;
+
+	for (i = 0; i < n; ++i) {
+		unsigned long address;
+		pte_t *pte;
+		unsigned int level;
+
+		address = (unsigned long) page_address(&p[i]);
+		pte = lookup_address(address, &level);
+		BUG_ON(!pte);
+		BUG_ON(level != PG_LEVEL_4K);
+
+		set_pte(pte, __pte(pte_val(*pte) | _PAGE_PRESENT));
+		set_pte(pte, __pte(pte_val(*pte) & ~_PAGE_HIDDEN));
+		__flush_tlb_one(address);
+	}
+}
+
+bool kmemcheck_page_is_tracked(struct page *p)
+{
+	/* This will also check the "hidden" flag of the PTE. */
+	return kmemcheck_pte_lookup((unsigned long) page_address(p));
+}
+
+void kmemcheck_hide_pages(struct page *p, unsigned int n)
+{
+	unsigned int i;
+
+	for (i = 0; i < n; ++i) {
+		unsigned long address;
+		pte_t *pte;
+		unsigned int level;
+
+		address = (unsigned long) page_address(&p[i]);
+		pte = lookup_address(address, &level);
+		BUG_ON(!pte);
+		BUG_ON(level != PG_LEVEL_4K);
+
+		set_pte(pte, __pte(pte_val(*pte) & ~_PAGE_PRESENT));
+		set_pte(pte, __pte(pte_val(*pte) | _PAGE_HIDDEN));
+		__flush_tlb_one(address);
+	}
+}
+
+/* Access may NOT cross page boundary */
+static void kmemcheck_read_strict(struct pt_regs *regs,
+	unsigned long addr, unsigned int size)
+{
+	void *shadow;
+	enum kmemcheck_shadow status;
+
+	shadow = kmemcheck_shadow_lookup(addr);
+	if (!shadow)
+		return;
+
+	kmemcheck_save_addr(addr);
+	status = kmemcheck_shadow_test(shadow, size);
+	if (status == KMEMCHECK_SHADOW_INITIALIZED)
+		return;
+
+	if (kmemcheck_enabled)
+		kmemcheck_error_save(status, addr, size, regs);
+
+	if (kmemcheck_enabled == 2)
+		kmemcheck_enabled = 0;
+
+	/* Don't warn about it again. */
+	kmemcheck_shadow_set(shadow, size);
+}
+
+/* Access may cross page boundary */
+static void kmemcheck_read(struct pt_regs *regs,
+	unsigned long addr, unsigned int size)
+{
+	unsigned long page = addr & PAGE_MASK;
+	unsigned long next_addr = addr + size - 1;
+	unsigned long next_page = next_addr & PAGE_MASK;
+
+	if (likely(page == next_page)) {
+		kmemcheck_read_strict(regs, addr, size);
+		return;
+	}
+
+	/*
+	 * What we do is basically to split the access across the
+	 * two pages and handle each part separately. Yes, this means
+	 * that we may now see reads that are 3 + 5 bytes, for
+	 * example (and if both are uninitialized, there will be two
+	 * reports), but it makes the code a lot simpler.
+	 */
+	kmemcheck_read_strict(regs, addr, next_page - addr);
+	kmemcheck_read_strict(regs, next_page, next_addr - next_page);
+}
+
+static void kmemcheck_write_strict(struct pt_regs *regs,
+	unsigned long addr, unsigned int size)
+{
+	void *shadow;
+
+	shadow = kmemcheck_shadow_lookup(addr);
+	if (!shadow)
+		return;
+
+	kmemcheck_save_addr(addr);
+	kmemcheck_shadow_set(shadow, size);
+}
+
+static void kmemcheck_write(struct pt_regs *regs,
+	unsigned long addr, unsigned int size)
+{
+	unsigned long page = addr & PAGE_MASK;
+	unsigned long next_addr = addr + size - 1;
+	unsigned long next_page = next_addr & PAGE_MASK;
+
+	if (likely(page == next_page)) {
+		kmemcheck_write_strict(regs, addr, size);
+		return;
+	}
+
+	/* See comment in kmemcheck_read(). */
+	kmemcheck_write_strict(regs, addr, next_page - addr);
+	kmemcheck_write_strict(regs, next_page, next_addr - next_page);
+}
+
+/*
+ * Copying is hard. We have two addresses, each of which may be split across
+ * a page (and each page will have different shadow addresses).
+ */
+static void kmemcheck_copy(struct pt_regs *regs,
+	unsigned long src_addr, unsigned long dst_addr, unsigned int size)
+{
+	uint8_t shadow[8];
+	enum kmemcheck_shadow status;
+
+	unsigned long page;
+	unsigned long next_addr;
+	unsigned long next_page;
+
+	uint8_t *x;
+	unsigned int i;
+	unsigned int n;
+
+	BUG_ON(size > sizeof(shadow));
+
+	page = src_addr & PAGE_MASK;
+	next_addr = src_addr + size - 1;
+	next_page = next_addr & PAGE_MASK;
+
+	if (likely(page == next_page)) {
+		/* Same page */
+		x = kmemcheck_shadow_lookup(src_addr);
+		if (x) {
+			kmemcheck_save_addr(src_addr);
+			for (i = 0; i < size; ++i)
+				shadow[i] = x[i];
+		} else {
+			for (i = 0; i < size; ++i)
+				shadow[i] = KMEMCHECK_SHADOW_INITIALIZED;
+		}
+	} else {
+		n = next_page - src_addr;
+		BUG_ON(n > sizeof(shadow));
+
+		/* First page */
+		x = kmemcheck_shadow_lookup(src_addr);
+		if (x) {
+			kmemcheck_save_addr(src_addr);
+			for (i = 0; i < n; ++i)
+				shadow[i] = x[i];
+		} else {
+			/* Not tracked */
+			for (i = 0; i < n; ++i)
+				shadow[i] = KMEMCHECK_SHADOW_INITIALIZED;
+		}
+
+		/* Second page */
+		x = kmemcheck_shadow_lookup(next_page);
+		if (x) {
+			kmemcheck_save_addr(next_page);
+			for (i = n; i < size; ++i)
+				shadow[i] = x[i - n];
+		} else {
+			/* Not tracked */
+			for (i = n; i < size; ++i)
+				shadow[i] = KMEMCHECK_SHADOW_INITIALIZED;
+		}
+	}
+
+	page = dst_addr & PAGE_MASK;
+	next_addr = dst_addr + size - 1;
+	next_page = next_addr & PAGE_MASK;
+
+	if (likely(page == next_page)) {
+		/* Same page */
+		x = kmemcheck_shadow_lookup(dst_addr);
+		if (x) {
+			kmemcheck_save_addr(dst_addr);
+			for (i = 0; i < size; ++i) {
+				x[i] = shadow[i];
+				shadow[i] = KMEMCHECK_SHADOW_INITIALIZED;
+			}
+		}
+	} else {
+		n = next_page - dst_addr;
+		BUG_ON(n > sizeof(shadow));
+
+		/* First page */
+		x = kmemcheck_shadow_lookup(dst_addr);
+		if (x) {
+			kmemcheck_save_addr(dst_addr);
+			for (i = 0; i < n; ++i) {
+				x[i] = shadow[i];
+				shadow[i] = KMEMCHECK_SHADOW_INITIALIZED;
+			}
+		}
+
+		/* Second page */
+		x = kmemcheck_shadow_lookup(next_page);
+		if (x) {
+			kmemcheck_save_addr(next_page);
+			for (i = n; i < size; ++i) {
+				x[i - n] = shadow[i];
+				shadow[i] = KMEMCHECK_SHADOW_INITIALIZED;
+			}
+		}
+	}
+
+	status = kmemcheck_shadow_test(shadow, size);
+	if (status == KMEMCHECK_SHADOW_INITIALIZED)
+		return;
+
+	if (kmemcheck_enabled)
+		kmemcheck_error_save(status, src_addr, size, regs);
+
+	if (kmemcheck_enabled == 2)
+		kmemcheck_enabled = 0;
+}
+
+enum kmemcheck_method {
+	KMEMCHECK_READ,
+	KMEMCHECK_WRITE,
+};
+
+static void kmemcheck_access(struct pt_regs *regs,
+	unsigned long fallback_address, enum kmemcheck_method fallback_method)
+{
+	const uint8_t *insn;
+	const uint8_t *insn_primary;
+	unsigned int size;
+
+	struct kmemcheck_context *data = &__get_cpu_var(kmemcheck_context);
+
+	/* Recursive fault -- ouch. */
+	if (data->busy) {
+		kmemcheck_show_addr(fallback_address);
+		kmemcheck_error_save_bug(regs);
+		return;
+	}
+
+	data->busy = true;
+
+	insn = (const uint8_t *) regs->ip;
+	insn_primary = kmemcheck_opcode_get_primary(insn);
+
+	kmemcheck_opcode_decode(insn, &size);
+
+	switch (insn_primary[0]) {
+#ifdef CONFIG_KMEMCHECK_BITOPS_OK
+		/* AND, OR, XOR */
+		/*
+		 * Unfortunately, these instructions have to be excluded from
+		 * our regular checking since they access only some (and not
+		 * all) bits. This clears out "bogus" bitfield-access warnings.
+		 */
+	case 0x80:
+	case 0x81:
+	case 0x82:
+	case 0x83:
+		switch ((insn_primary[1] >> 3) & 7) {
+			/* OR */
+		case 1:
+			/* AND */
+		case 4:
+			/* XOR */
+		case 6:
+			kmemcheck_write(regs, fallback_address, size);
+			goto out;
+
+			/* ADD */
+		case 0:
+			/* ADC */
+		case 2:
+			/* SBB */
+		case 3:
+			/* SUB */
+		case 5:
+			/* CMP */
+		case 7:
+			break;
+		}
+		break;
+#endif
+
+		/* MOVS, MOVSB, MOVSW, MOVSD */
+	case 0xa4:
+	case 0xa5:
+		/*
+		 * These instructions are special because they take two
+		 * addresses, but we only get one page fault.
+		 */
+		kmemcheck_copy(regs, regs->si, regs->di, size);
+		goto out;
+
+		/* CMPS, CMPSB, CMPSW, CMPSD */
+	case 0xa6:
+	case 0xa7:
+		kmemcheck_read(regs, regs->si, size);
+		kmemcheck_read(regs, regs->di, size);
+		goto out;
+	}
+
+	/*
+	 * If the opcode isn't special in any way, we use the data from the
+	 * page fault handler to determine the address and type of memory
+	 * access.
+	 */
+	switch (fallback_method) {
+	case KMEMCHECK_READ:
+		kmemcheck_read(regs, fallback_address, size);
+		goto out;
+	case KMEMCHECK_WRITE:
+		kmemcheck_write(regs, fallback_address, size);
+		goto out;
+	}
+
+out:
+	data->busy = false;
+}
+
+bool kmemcheck_fault(struct pt_regs *regs, unsigned long address,
+	unsigned long error_code)
+{
+	pte_t *pte;
+	unsigned int level;
+
+	/*
+	 * XXX: Is it safe to assume that memory accesses from virtual 86
+	 * mode or non-kernel code segments will _never_ access kernel
+	 * memory (e.g. tracked pages)? For now, we need this to avoid
+	 * invoking kmemcheck for PnP BIOS calls.
+	 */
+	if (regs->flags & X86_VM_MASK)
+		return false;
+	if (regs->cs != __KERNEL_CS)
+		return false;
+
+	pte = lookup_address(address, &level);
+	if (!pte)
+		return false;
+	if (level != PG_LEVEL_4K)
+		return false;
+	if (!pte_hidden(*pte))
+		return false;
+
+	if (error_code & 2)
+		kmemcheck_access(regs, address, KMEMCHECK_WRITE);
+	else
+		kmemcheck_access(regs, address, KMEMCHECK_READ);
+
+	kmemcheck_show(regs);
+	return true;
+}
+
+bool kmemcheck_trap(struct pt_regs *regs)
+{
+	if (!kmemcheck_active(regs))
+		return false;
+
+	/* We're done. */
+	kmemcheck_hide(regs);
+	return true;
+}