livepatch: Use the default ftrace_ops instead of REGS when ARGS is available

When CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS is available, the ftrace call
will be able to set the ip of the calling function. This will improve the
performance of live kernel patching where it does not need all the regs to
be stored just to change the instruction pointer.

If all archs that support live kernel patching also support
HAVE_DYNAMIC_FTRACE_WITH_ARGS, then the architecture specific function
klp_arch_set_pc() could be made generic.

It is possible that an arch can support HAVE_DYNAMIC_FTRACE_WITH_ARGS but
not HAVE_DYNAMIC_FTRACE_WITH_REGS and then have access to live patching.

Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: live-patching@vger.kernel.org
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/arch/powerpc/include/asm/livepatch.h b/arch/powerpc/include/asm/livepatch.h
index 4a3d5d2..ae25e6e 100644 (file)
--- a/arch/powerpc/include/asm/livepatch.h
+++ b/arch/powerpc/include/asm/livepatch.h
@@ -12,8 +12,10 @@
 #include <linux/sched/task_stack.h>
 
 #ifdef CONFIG_LIVEPATCH
-static inline void klp_arch_set_pc(struct pt_regs *regs, unsigned long ip)
+static inline void klp_arch_set_pc(struct ftrace_regs *fregs, unsigned long ip)
 {
+       struct pt_regs *regs = ftrace_get_regs(fregs);
+
        regs->nip = ip;
 }
 

diff --git a/arch/s390/include/asm/livepatch.h b/arch/s390/include/asm/livepatch.h
index 818612b..d578a8c 100644 (file)
--- a/arch/s390/include/asm/livepatch.h
+++ b/arch/s390/include/asm/livepatch.h
@@ -11,10 +11,13 @@
 #ifndef ASM_LIVEPATCH_H
 #define ASM_LIVEPATCH_H
 
+#include <linux/ftrace.h>
 #include <asm/ptrace.h>
 
-static inline void klp_arch_set_pc(struct pt_regs *regs, unsigned long ip)
+static inline void klp_arch_set_pc(struct ftrace_regs *fregs, unsigned long ip)
 {
+       struct pt_regs *regs = ftrace_get_regs(fregs);
+
        regs->psw.addr = ip;
 }
 

diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h
index e00fe88..9f3130f 100644 (file)
--- a/arch/x86/include/asm/ftrace.h
+++ b/arch/x86/include/asm/ftrace.h
@@ -54,6 +54,9 @@ arch_ftrace_get_regs(struct ftrace_regs *fregs)
                return NULL;
        return &fregs->regs;
 }
+
+#define ftrace_instruction_pointer_set(fregs, _ip)     \
+       do { (fregs)->regs.ip = (_ip); } while (0)
 #endif
 
 #ifdef CONFIG_DYNAMIC_FTRACE

diff --git a/arch/x86/include/asm/livepatch.h b/arch/x86/include/asm/livepatch.h
index 1fde1ab..7c5cc66 100644 (file)
--- a/arch/x86/include/asm/livepatch.h
+++ b/arch/x86/include/asm/livepatch.h
@@ -12,9 +12,9 @@
 #include <asm/setup.h>
 #include <linux/ftrace.h>
 
-static inline void klp_arch_set_pc(struct pt_regs *regs, unsigned long ip)
+static inline void klp_arch_set_pc(struct ftrace_regs *fregs, unsigned long ip)
 {
-       regs->ip = ip;
+       ftrace_instruction_pointer_set(fregs, ip);
 }
 
 #endif /* _ASM_X86_LIVEPATCH_H */

diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S
index 60e3b64..0d54099 100644 (file)
--- a/arch/x86/kernel/ftrace_64.S
+++ b/arch/x86/kernel/ftrace_64.S
@@ -157,6 +157,10 @@ SYM_INNER_LABEL(ftrace_caller_op_ptr, SYM_L_GLOBAL)
 SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL)
        call ftrace_stub
 
+       /* Handlers can change the RIP */
+       movq RIP(%rsp), %rax
+       movq %rax, MCOUNT_REG_SIZE(%rsp)
+
        restore_mcount_regs
 
        /*

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 588ea70..9a8ce28 100644 (file)
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -97,6 +97,13 @@ struct ftrace_regs {
 };
 #define arch_ftrace_get_regs(fregs) (&(fregs)->regs)
 
+/*
+ * ftrace_instruction_pointer_set() is to be defined by the architecture
+ * if to allow setting of the instruction pointer from the ftrace_regs
+ * when HAVE_DYNAMIC_FTRACE_WITH_ARGS is set and it supports
+ * live kernel patching.
+ */
+#define ftrace_instruction_pointer_set(fregs, ip) do { } while (0)
 #endif /* CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS */
 
 static __always_inline struct pt_regs *ftrace_get_regs(struct ftrace_regs *fregs)

diff --git a/kernel/livepatch/Kconfig b/kernel/livepatch/Kconfig
index 54102de..53d51ed 100644 (file)
--- a/kernel/livepatch/Kconfig
+++ b/kernel/livepatch/Kconfig
@@ -6,7 +6,7 @@ config HAVE_LIVEPATCH
 
 config LIVEPATCH
        bool "Kernel Live Patching"
-       depends on DYNAMIC_FTRACE_WITH_REGS
+       depends on DYNAMIC_FTRACE_WITH_REGS || DYNAMIC_FTRACE_WITH_ARGS
        depends on MODULES
        depends on SYSFS
        depends on KALLSYMS_ALL

diff --git a/kernel/livepatch/patch.c b/kernel/livepatch/patch.c
index f89f9e7..e8029ae 100644 (file)
--- a/kernel/livepatch/patch.c
+++ b/kernel/livepatch/patch.c
@@ -42,7 +42,6 @@ static void notrace klp_ftrace_handler(unsigned long ip,
                                       struct ftrace_ops *fops,
                                       struct ftrace_regs *fregs)
 {
-       struct pt_regs *regs = ftrace_get_regs(fregs);
        struct klp_ops *ops;
        struct klp_func *func;
        int patch_state;
@@ -118,7 +117,7 @@ static void notrace klp_ftrace_handler(unsigned long ip,
        if (func->nop)
                goto unlock;
 
-       klp_arch_set_pc(regs, (unsigned long)func->new_func);
+       klp_arch_set_pc(fregs, (unsigned long)func->new_func);
 
 unlock:
        preempt_enable_notrace();
@@ -200,8 +199,10 @@ static int klp_patch_func(struct klp_func *func)
                        return -ENOMEM;
 
                ops->fops.func = klp_ftrace_handler;
-               ops->fops.flags = FTRACE_OPS_FL_SAVE_REGS |
-                                 FTRACE_OPS_FL_DYNAMIC |
+               ops->fops.flags = FTRACE_OPS_FL_DYNAMIC |
+#ifndef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS
+                                 FTRACE_OPS_FL_SAVE_REGS |
+#endif
                                  FTRACE_OPS_FL_IPMODIFY |
                                  FTRACE_OPS_FL_PERMANENT;