[PATCH] kprobes: fix single-step out of line - take2
From: Ananth N Mavinakayanahalli (ananth_at_in.ibm.com)
Date: 06/17/05
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Date: Fri, 17 Jun 2005 11:23:06 -0400 To: linuxppc64-dev@ozlabs.org, linux-kernel@vger.kernel.org
Hi,
Here is the second try to fix the single-step out of line issues for
PPC64 now that the kernel has no-execute support.
x86_64 also has no-execute support and kprobes on x86_64 solved this
issue by allocating an executable kernel page and using it as a scratch
area for instructions to be stepped out of line. Reuse that for PPC64 too.
Thanks,
Ananth
Now that PPC64 has no-execute support, here is a second try to fix the
single step out of line during kprobe execution. Kprobes on x86_64 already
solved this problem by allocating an executable page and using it as the
scratch area for stepping out of line. Reuse that.
Patch against 2.6.12-rc6-git8
Signed-off-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
arch/ppc64/kernel/kprobes.c | 26 ++++++++-
arch/x86_64/kernel/kprobes.c | 112 -------------------------------------------
include/asm-ppc64/kprobes.h | 2
include/linux/kprobes.h | 2
kernel/kprobes.c | 101 ++++++++++++++++++++++++++++++++++++++
5 files changed, 126 insertions(+), 117 deletions(-)
Index: linux-2.6.12-rc6/arch/ppc64/kernel/kprobes.c
===================================================================
--- linux-2.6.12-rc6.orig/arch/ppc64/kernel/kprobes.c 2005-06-16 14:44:40.000000000 -0400
+++ linux-2.6.12-rc6/arch/ppc64/kernel/kprobes.c 2005-06-16 14:53:51.000000000 -0400
@@ -39,6 +39,8 @@
#define KPROBE_HIT_ACTIVE 0x00000001
#define KPROBE_HIT_SS 0x00000002
+static DECLARE_MUTEX(kprobe_mutex);
+
static struct kprobe *current_kprobe;
static unsigned long kprobe_status, kprobe_saved_msr;
static struct pt_regs jprobe_saved_regs;
@@ -55,6 +57,15 @@ int arch_prepare_kprobe(struct kprobe *p
printk("Cannot register a kprobe on rfid or mtmsrd\n");
ret = -EINVAL;
}
+
+ /* insn must be on a special executable page on ppc64 */
+ if (!ret) {
+ up(&kprobe_mutex);
+ p->ainsn.insn = get_insn_slot();
+ down(&kprobe_mutex);
+ if (!p->ainsn.insn)
+ ret = -ENOMEM;
+ }
return ret;
}
@@ -65,6 +76,9 @@ void arch_copy_kprobe(struct kprobe *p)
void arch_remove_kprobe(struct kprobe *p)
{
+ up(&kprobe_mutex);
+ free_insn_slot(p->ainsn.insn);
+ down(&kprobe_mutex);
}
static inline void disarm_kprobe(struct kprobe *p, struct pt_regs *regs)
@@ -75,12 +89,15 @@ static inline void disarm_kprobe(struct
static inline void prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
{
+ kprobe_opcode_t insn = *p->ainsn.insn;
+
regs->msr |= MSR_SE;
- /*single step inline if it a breakpoint instruction*/
- if (p->opcode == BREAKPOINT_INSTRUCTION)
+
+ /* single step inline if it is a trap variant */
+ if (IS_TW(insn) || IS_TD(insn) || IS_TWI(insn) || IS_TDI(insn))
regs->nip = (unsigned long)p->addr;
else
- regs->nip = (unsigned long)&p->ainsn.insn;
+ regs->nip = (unsigned long)p->ainsn.insn;
}
static inline int kprobe_handler(struct pt_regs *regs)
@@ -172,9 +189,10 @@ no_kprobe:
static void resume_execution(struct kprobe *p, struct pt_regs *regs)
{
int ret;
+ unsigned int insn = *p->ainsn.insn;
regs->nip = (unsigned long)p->addr;
- ret = emulate_step(regs, p->ainsn.insn[0]);
+ ret = emulate_step(regs, insn);
if (ret == 0)
regs->nip = (unsigned long)p->addr + 4;
}
Index: linux-2.6.12-rc6/arch/x86_64/kernel/kprobes.c
===================================================================
--- linux-2.6.12-rc6.orig/arch/x86_64/kernel/kprobes.c 2005-06-06 11:22:29.000000000 -0400
+++ linux-2.6.12-rc6/arch/x86_64/kernel/kprobes.c 2005-06-16 14:58:38.000000000 -0400
@@ -36,7 +36,6 @@
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/preempt.h>
-#include <linux/moduleloader.h>
#include <asm/pgtable.h>
#include <asm/kdebug.h>
@@ -51,8 +50,6 @@ static struct kprobe *current_kprobe;
static unsigned long kprobe_status, kprobe_old_rflags, kprobe_saved_rflags;
static struct pt_regs jprobe_saved_regs;
static long *jprobe_saved_rsp;
-static kprobe_opcode_t *get_insn_slot(void);
-static void free_insn_slot(kprobe_opcode_t *slot);
void jprobe_return_end(void);
/* copy of the kernel stack at the probe fire time */
@@ -527,112 +524,3 @@ int longjmp_break_handler(struct kprobe
}
return 0;
}
-
-/*
- * kprobe->ainsn.insn points to the copy of the instruction to be single-stepped.
- * By default on x86_64, pages we get from kmalloc or vmalloc are not
- * executable. Single-stepping an instruction on such a page yields an
- * oops. So instead of storing the instruction copies in their respective
- * kprobe objects, we allocate a page, map it executable, and store all the
- * instruction copies there. (We can allocate additional pages if somebody
- * inserts a huge number of probes.) Each page can hold up to INSNS_PER_PAGE
- * instruction slots, each of which is MAX_INSN_SIZE*sizeof(kprobe_opcode_t)
- * bytes.
- */
-#define INSNS_PER_PAGE (PAGE_SIZE/(MAX_INSN_SIZE*sizeof(kprobe_opcode_t)))
-struct kprobe_insn_page {
- struct hlist_node hlist;
- kprobe_opcode_t *insns; /* page of instruction slots */
- char slot_used[INSNS_PER_PAGE];
- int nused;
-};
-
-static struct hlist_head kprobe_insn_pages;
-
-/**
- * get_insn_slot() - Find a slot on an executable page for an instruction.
- * We allocate an executable page if there's no room on existing ones.
- */
-static kprobe_opcode_t *get_insn_slot(void)
-{
- struct kprobe_insn_page *kip;
- struct hlist_node *pos;
-
- hlist_for_each(pos, &kprobe_insn_pages) {
- kip = hlist_entry(pos, struct kprobe_insn_page, hlist);
- if (kip->nused < INSNS_PER_PAGE) {
- int i;
- for (i = 0; i < INSNS_PER_PAGE; i++) {
- if (!kip->slot_used[i]) {
- kip->slot_used[i] = 1;
- kip->nused++;
- return kip->insns + (i*MAX_INSN_SIZE);
- }
- }
- /* Surprise! No unused slots. Fix kip->nused. */
- kip->nused = INSNS_PER_PAGE;
- }
- }
-
- /* All out of space. Need to allocate a new page. Use slot 0.*/
- kip = kmalloc(sizeof(struct kprobe_insn_page), GFP_KERNEL);
- if (!kip) {
- return NULL;
- }
-
- /*
- * For the %rip-relative displacement fixups to be doable, we
- * need our instruction copy to be within +/- 2GB of any data it
- * might access via %rip. That is, within 2GB of where the
- * kernel image and loaded module images reside. So we allocate
- * a page in the module loading area.
- */
- kip->insns = module_alloc(PAGE_SIZE);
- if (!kip->insns) {
- kfree(kip);
- return NULL;
- }
- INIT_HLIST_NODE(&kip->hlist);
- hlist_add_head(&kip->hlist, &kprobe_insn_pages);
- memset(kip->slot_used, 0, INSNS_PER_PAGE);
- kip->slot_used[0] = 1;
- kip->nused = 1;
- return kip->insns;
-}
-
-/**
- * free_insn_slot() - Free instruction slot obtained from get_insn_slot().
- */
-static void free_insn_slot(kprobe_opcode_t *slot)
-{
- struct kprobe_insn_page *kip;
- struct hlist_node *pos;
-
- hlist_for_each(pos, &kprobe_insn_pages) {
- kip = hlist_entry(pos, struct kprobe_insn_page, hlist);
- if (kip->insns <= slot
- && slot < kip->insns+(INSNS_PER_PAGE*MAX_INSN_SIZE)) {
- int i = (slot - kip->insns) / MAX_INSN_SIZE;
- kip->slot_used[i] = 0;
- kip->nused--;
- if (kip->nused == 0) {
- /*
- * Page is no longer in use. Free it unless
- * it's the last one. We keep the last one
- * so as not to have to set it up again the
- * next time somebody inserts a probe.
- */
- hlist_del(&kip->hlist);
- if (hlist_empty(&kprobe_insn_pages)) {
- INIT_HLIST_NODE(&kip->hlist);
- hlist_add_head(&kip->hlist,
- &kprobe_insn_pages);
- } else {
- module_free(NULL, kip->insns);
- kfree(kip);
- }
- }
- return;
- }
- }
-}
Index: linux-2.6.12-rc6/include/linux/kprobes.h
===================================================================
--- linux-2.6.12-rc6.orig/include/linux/kprobes.h 2005-06-06 11:22:29.000000000 -0400
+++ linux-2.6.12-rc6/include/linux/kprobes.h 2005-06-16 15:01:13.000000000 -0400
@@ -101,6 +101,8 @@ extern int arch_prepare_kprobe(struct kp
extern void arch_copy_kprobe(struct kprobe *p);
extern void arch_remove_kprobe(struct kprobe *p);
extern void show_registers(struct pt_regs *regs);
+extern kprobe_opcode_t *get_insn_slot(void);
+extern void free_insn_slot(kprobe_opcode_t *slot);
/* Get the kprobe at this addr (if any). Must have called lock_kprobes */
struct kprobe *get_kprobe(void *addr);
Index: linux-2.6.12-rc6/kernel/kprobes.c
===================================================================
--- linux-2.6.12-rc6.orig/kernel/kprobes.c 2005-06-06 11:22:29.000000000 -0400
+++ linux-2.6.12-rc6/kernel/kprobes.c 2005-06-17 08:50:47.000000000 -0400
@@ -33,6 +33,7 @@
#include <linux/hash.h>
#include <linux/init.h>
#include <linux/module.h>
+#include <linux/moduleloader.h>
#include <asm/cacheflush.h>
#include <asm/errno.h>
#include <asm/kdebug.h>
@@ -46,6 +47,106 @@ unsigned int kprobe_cpu = NR_CPUS;
static DEFINE_SPINLOCK(kprobe_lock);
static struct kprobe *curr_kprobe;
+/*
+ * kprobe->ainsn.insn points to the copy of the instruction to be
+ * single-stepped. x86_64, POWER4 and above have no-exec support and
+ * stepping on the instruction on a vmalloced/kmalloced/data page
+ * is a recipe for disaster
+ */
+#define INSNS_PER_PAGE (PAGE_SIZE/(MAX_INSN_SIZE * sizeof(kprobe_opcode_t)))
+
+struct kprobe_insn_page {
+ struct hlist_node hlist;
+ kprobe_opcode_t *insns; /* Page of instruction slots */
+ char slot_used[INSNS_PER_PAGE];
+ int nused;
+};
+
+static struct hlist_head kprobe_insn_pages;
+
+/**
+ * get_insn_slot() - Find a slot on an executable page for an instruction.
+ * We allocate an executable page if there's no room on existing ones.
+ */
+kprobe_opcode_t *get_insn_slot(void)
+{
+ struct kprobe_insn_page *kip;
+ struct hlist_node *pos;
+
+ hlist_for_each(pos, &kprobe_insn_pages) {
+ kip = hlist_entry(pos, struct kprobe_insn_page, hlist);
+ if (kip->nused < INSNS_PER_PAGE) {
+ int i;
+ for (i = 0; i < INSNS_PER_PAGE; i++) {
+ if (!kip->slot_used[i]) {
+ kip->slot_used[i] = 1;
+ kip->nused++;
+ return kip->insns + (i * MAX_INSN_SIZE);
+ }
+ }
+ /* Surprise! No unused slots. Fix kip->nused. */
+ kip->nused = INSNS_PER_PAGE;
+ }
+ }
+
+ /* All out of space. Need to allocate a new page. Use slot 0.*/
+ kip = kmalloc(sizeof(struct kprobe_insn_page), GFP_KERNEL);
+ if (!kip) {
+ return NULL;
+ }
+
+ /*
+ * Use module_alloc so this page is within +/- 2GB of where the
+ * kernel image and loaded module images reside. This is required
+ * so x86_64 can correctly handle the %rip-relative fixups.
+ */
+ kip->insns = module_alloc(PAGE_SIZE);
+ if (!kip->insns) {
+ kfree(kip);
+ return NULL;
+ }
+ INIT_HLIST_NODE(&kip->hlist);
+ hlist_add_head(&kip->hlist, &kprobe_insn_pages);
+ memset(kip->slot_used, 0, INSNS_PER_PAGE);
+ kip->slot_used[0] = 1;
+ kip->nused = 1;
+ return kip->insns;
+}
+
+void free_insn_slot(kprobe_opcode_t *slot)
+{
+ struct kprobe_insn_page *kip;
+ struct hlist_node *pos;
+
+ hlist_for_each(pos, &kprobe_insn_pages) {
+ kip = hlist_entry(pos, struct kprobe_insn_page, hlist);
+ if (kip->insns <= slot &&
+ slot < kip->insns + (INSNS_PER_PAGE * MAX_INSN_SIZE)) {
+ int i = (slot - kip->insns) / MAX_INSN_SIZE;
+ kip->slot_used[i] = 0;
+ kip->nused--;
+ if (kip->nused == 0) {
+ /*
+ * Page is no longer in use. Free it unless
+ * it's the last one. We keep the last one
+ * so as not to have to set it up again the
+ * next time somebody inserts a probe.
+ */
+ hlist_del(&kip->hlist);
+ if (hlist_empty(&kprobe_insn_pages)) {
+ INIT_HLIST_NODE(&kip->hlist);
+ hlist_add_head(&kip->hlist,
+ &kprobe_insn_pages);
+ } else {
+ module_free(NULL, kip->insns);
+ kfree(kip);
+ }
+ }
+ return;
+ }
+ }
+}
+
/* Locks kprobe: irqs must be disabled */
void lock_kprobes(void)
{
Index: linux-2.6.12-rc6/include/asm-ppc64/kprobes.h
===================================================================
--- linux-2.6.12-rc6.orig/include/asm-ppc64/kprobes.h 2005-06-17 09:32:24.000000000 -0400
+++ linux-2.6.12-rc6/include/asm-ppc64/kprobes.h 2005-06-17 09:32:49.000000000 -0400
@@ -45,7 +45,7 @@ typedef unsigned int kprobe_opcode_t;
/* Architecture specific copy of original instruction */
struct arch_specific_insn {
/* copy of original instruction */
- kprobe_opcode_t insn[MAX_INSN_SIZE];
+ kprobe_opcode_t *insn;
};
#ifdef CONFIG_KPROBES
-
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