[PATCH 3/3 v7] livepatch: Use the default ftrace_ops instead of REGS when ARGS is available

[PATCH 3/3 v7] livepatch: Use the default ftrace_ops instead of REGS when ARGS is available

[Steven Rostedt]

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

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>
---
Changes since v6:
 - Updated to use ftrace_instruction_pointer_set() macro

 arch/powerpc/include/asm/livepatch.h | 4 +++-
 arch/s390/include/asm/livepatch.h    | 5 ++++-
 arch/x86/include/asm/ftrace.h        | 3 +++
 arch/x86/include/asm/livepatch.h     | 4 ++--
 arch/x86/kernel/ftrace_64.S          | 4 ++++
 include/linux/ftrace.h               | 7 +++++++
 kernel/livepatch/Kconfig             | 2 +-
 kernel/livepatch/patch.c             | 9 +++++----
 8 files changed, 29 insertions(+), 9 deletions(-)

diff --git a/arch/powerpc/include/asm/livepatch.h b/arch/powerpc/include/asm/livepatch.h
index 4a3d5d25fed5..ae25e6e72997 100644
--- 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 818612b784cd..d578a8c76676 100644
--- 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 e00fe88146e0..9f3130f40807 100644
--- 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 1fde1ab6559e..7c5cc6660e4b 100644
--- 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 60e3b64f5ea6..0d54099c2a3a 100644
--- 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 588ea7023a7a..9a8ce28e4485 100644
--- 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 54102deb50ba..53d51ed619a3 100644
--- 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 f89f9e7e9b07..e8029aea67f1 100644
--- 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;
 
-- 
2.28.0

Re: [PATCH 3/3 v7] livepatch: Use the default ftrace_ops instead of REGS when ARGS is available

[Petr Mladek]

On Fri 2020-11-13 12:18:14, Steven Rostedt wrote:
> From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
> 
> 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>
> ---
> Changes since v6:
>  - Updated to use ftrace_instruction_pointer_set() macro
> 
>  arch/powerpc/include/asm/livepatch.h | 4 +++-
>  arch/s390/include/asm/livepatch.h    | 5 ++++-
>  arch/x86/include/asm/ftrace.h        | 3 +++
>  arch/x86/include/asm/livepatch.h     | 4 ++--
>  arch/x86/kernel/ftrace_64.S          | 4 ++++
>  include/linux/ftrace.h               | 7 +++++++
>  kernel/livepatch/Kconfig             | 2 +-
>  kernel/livepatch/patch.c             | 9 +++++----
>  8 files changed, 29 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/livepatch.h b/arch/powerpc/include/asm/livepatch.h
> index 4a3d5d25fed5..ae25e6e72997 100644
> --- 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);

Should we check for NULL pointer here?

> +
>  	regs->nip = ip;
>  }
>  
> diff --git a/arch/s390/include/asm/livepatch.h b/arch/s390/include/asm/livepatch.h
> index 818612b784cd..d578a8c76676 100644
> --- 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);

And here?

> +
>  	regs->psw.addr = ip;
>  }
>  

Otherwise, it looks for me.

Best Regards,
Petr

Re: [PATCH 3/3 v7] livepatch: Use the default ftrace_ops instead of REGS when ARGS is available

[Steven Rostedt]

On Thu, 19 Nov 2020 12:52:00 +0100
Petr Mladek <pmladek@suse.com> wrote:

> >  #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);  
> 
> Should we check for NULL pointer here?

As mentioned in my last email. regs could have been NULL for the same
reasons before this patch, and we didn't check it then. Why should we check
it now?

The ftrace_get_regs() only makes sure that a ftrace_ops that set
FL_SAVE_REGS gets it, and those that did not, don't.

But that's not entirely true either. If there's two callbacks to the same
function, and one has FL_SAVE_REGS set, they both can have access to the
regs (before and after this patch). It's just that the one that did not
have FL_SAVE_REGS set, isn't guaranteed to have it.

-- Steve


> 
> > +
> >  	regs->nip = ip;
> >  }

Re: [PATCH 3/3 v7] livepatch: Use the default ftrace_ops instead of REGS when ARGS is available

[Petr Mladek]

On Thu 2020-11-19 09:12:35, Steven Rostedt wrote:
> On Thu, 19 Nov 2020 12:52:00 +0100
> Petr Mladek <pmladek@suse.com> wrote:
> 
> > >  #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);  
> > 
> > Should we check for NULL pointer here?
> 
> As mentioned in my last email. regs could have been NULL for the same
> reasons before this patch, and we didn't check it then. Why should we check
> it now?
> 
> The ftrace_get_regs() only makes sure that a ftrace_ops that set
> FL_SAVE_REGS gets it, and those that did not, don't.
> 
> But that's not entirely true either. If there's two callbacks to the same
> function, and one has FL_SAVE_REGS set, they both can have access to the
> regs (before and after this patch). It's just that the one that did not
> have FL_SAVE_REGS set, isn't guaranteed to have it.

Makes sense. Thanks for explanation. Feel free to use:

Acked-by: Petr Mladek <pmladek@suse.com>

I actually did review of all patches and they looked fine to me.
I just did not check all corner cases, assembly, and did not test
it, so I give it just my ack. I believe your testing ;-)

Best Regards,
Petr