[PATCH] kprobes: fix single-step out of line - take2
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.
Signed-off-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 334f374..6524252 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -36,6 +36,7 @@
#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>
@@ -50,6 +51,106 @@
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)
{