[PATCH v3 17/39] x86/livepatch: Validate __fentry__ location

Peter Zijlstra
2022-03-03T11:33:45Z

Currently livepatch assumes __fentry__ lives at func+0, which is most
likely untrue with IBT on. Instead make it use ftrace_location() by
default which both validates and finds the actual ip if there is any
in the same symbol.

Suggested-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/powerpc/include/asm/livepatch.h | 10 ----------
kernel/livepatch/patch.c | 19 ++-----------------
2 files changed, 2 insertions(+), 27 deletions(-)

--- a/arch/powerpc/include/asm/livepatch.h
+++ b/arch/powerpc/include/asm/livepatch.h
@@ -19,16 +19,6 @@ static inline void klp_arch_set_pc(struc
regs_set_return_ip(regs, ip);
}

-#define klp_get_ftrace_location klp_get_ftrace_location
-static inline unsigned long klp_get_ftrace_location(unsigned long faddr)
-{
- /*
- * Live patch works only with -mprofile-kernel on PPC. In this case,
- * the ftrace location is always within the first 16 bytes.
- */
- return ftrace_location_range(faddr, faddr + 16);
-}
-
static inline void klp_init_thread_info(struct task_struct *p)
{
/* + 1 to account for STACK_END_MAGIC */
--- a/kernel/livepatch/patch.c
+++ b/kernel/livepatch/patch.c
@@ -124,19 +124,6 @@ static void notrace klp_ftrace_handler(u
ftrace_test_recursion_unlock(bit);
}

-/*
- * Convert a function address into the appropriate ftrace location.
- *
- * Usually this is just the address of the function, but on some architectures
- * it's more complicated so allow them to provide a custom behaviour.
- */
-#ifndef klp_get_ftrace_location
-static unsigned long klp_get_ftrace_location(unsigned long faddr)
-{
- return faddr;
-}
-#endif
-
static void klp_unpatch_func(struct klp_func *func)
{
struct klp_ops *ops;
@@ -153,8 +140,7 @@ static void klp_unpatch_func(struct klp_
if (list_is_singular(&ops->func_stack)) {
unsigned long ftrace_loc;

- ftrace_loc =
- klp_get_ftrace_location((unsigned long)func->old_func);
+ ftrace_loc = ftrace_location((unsigned long)func->old_func);
if (WARN_ON(!ftrace_loc))
return;

@@ -186,8 +172,7 @@ static int klp_patch_func(struct klp_fun
if (!ops) {
unsigned long ftrace_loc;

- ftrace_loc =
- klp_get_ftrace_location((unsigned long)func->old_func);
+ ftrace_loc = ftrace_location((unsigned long)func->old_func);
if (!ftrace_loc) {
pr_err("failed to find location for function '%s'\n",
func->old_name);