From: Pekka Paalanen <[EMAIL PROTECTED]>
Provides kernel modules a way to register custom page fault handlers.
On every page fault, except those handled in vmalloc_fault(), this will
call a list of registered functions. The functions may handle the fault
and force do_page_fault() to return immediately.
This functionality is similar to the now removed page fault notifiers.
Custom page fault handlers are used by debugging and reverse engineering
tools. Mmio-trace is one such tool and a patch to add it into the tree
will follow.
The custom page fault handlers are called from the exact same points in
do_page_fault() as the page fault notifiers were.
Signed-off-by: Pekka Paalanen <[EMAIL PROTECTED]>
Signed-off-by: Harvey Harrison <[EMAIL PROTECTED]>
---
Ingo, ported Pekka's patch to current x86.git for review. I have not
incorporated the RCU comments from Peter Zjistra, but I have folded
some of the static functions into on handle_custom_pf function that
will match the handle_kprobe_fault helper that will be ready for
RC1.
Harvey
arch/x86/Kconfig.debug | 9 ++++++++
arch/x86/mm/fault.c | 51
++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 60 insertions(+), 0 deletions(-)
diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
index 2e1e3af..9b44bc5 100644
--- a/arch/x86/Kconfig.debug
+++ b/arch/x86/Kconfig.debug
@@ -225,4 +225,13 @@ config CPA_DEBUG
help
Do change_page_attr self tests at boot.
+config PAGE_FAULT_HANDLERS
+ bool "Custom page fault handlers"
+ depends on DEBUG_KERNEL
+ help
+ Allow the use of custom page fault handlers. A kernel module may
+ register a function that is called on every page fault not handled
+ for vmalloc. Custom handlers are used by some debugging and reverse
+ engineering tools.
+
endmenu
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index e28cc52..c6c8164 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -49,6 +49,54 @@
#define PF_RSVD (1<<3)
#define PF_INSTR (1<<4)
+#ifdef CONFIG_PAGE_FAULT_HANDLERS
+static HLIST_HEAD(pf_handlers); /* protected by RCU */
+static DEFINE_SPINLOCK(pf_handlers_writer);
+
+void register_page_fault_handler(struct pf_handler *new_pfh)
+{
+ spin_lock(&pf_handlers_writer);
+ hlist_add_head_rcu(&new_pfh->hlist, &pf_handlers);
+ spin_unlock(&pf_handlers_writer);
+}
+EXPORT_SYMBOL_GPL(register_page_fault_handler);
+
+void unregister_page_fault_handler(struct pf_handler *old_pfh)
+{
+ might_sleep();
+ spin_lock(&pf_handlers_writer);
+ hlist_del_rcu(&old_pfh->hlist);
+ spin_unlock(&pf_handlers_writer);
+ synchronize_rcu();
+}
+EXPORT_SYMBOL_GPL(unregister_page_fault_handler);
+#endif
+
+/* returns non-zero if do_page_fault() should return */
+static int handle_custom_pf(struct pt_regs *regs, unsigned long
error_code,
+ unsigned long address)
+{
+#ifdef CONFIG_PAGE_FAULT_HANDLERS
+ int ret = 0;
+ struct pf_handler *cur;
+ struct hlist_node *ncur;
+
+ if (hlist_empty(&pf_handlers))
+ return 0;
+
+ rcu_read_lock();
+ hlist_for_each_entry_rcu(cur, ncur, &pf_handlers, hlist) {
+ ret = cur->handler(regs, error_code, address);
+ if (ret)
+ break;
+ }
+ rcu_read_unlock();
+ return ret;
+#else
+ return 0;
+#endif
+}
+
static inline int notify_page_fault(struct pt_regs *regs)
{
#ifdef CONFIG_KPROBES
@@ -588,6 +636,9 @@ void __kprobes do_page_fault(struct pt_regs *regs,
unsigned long error_code)
if (notify_page_fault(regs))
return;
+ if (handle_custom_pf(regs, error_code, address))
+ return;
+
/*
* We fault-in kernel-space virtual memory on-demand. The
* 'reference' page table is init_mm.pgd.
--
1.5.4.rc4.1142.gf5a97
--
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