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Date: Thu, 25 Jul 2019 22:07:52 -0400
From: Joe Lawrence <joe.lawrence@...hat.com>
To: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Steven Rostedt <rostedt@...dmis.org>,
Ingo Molnar <mingo@...nel.org>,
Josh Poimboeuf <jpoimboe@...hat.com>,
live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
"Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>,
Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
"David S . Miller" <davem@...emloft.net>
Subject: Re: [PATCH] kprobes: Allow kprobes coexist with livepatch
On Thu, Jul 25, 2019 at 03:24:37PM +0900, Masami Hiramatsu wrote:
> Allow kprobes which do not modify regs->ip, coexist with livepatch
> by dropping FTRACE_OPS_FL_IPMODIFY from ftrace_ops.
>
> User who wants to modify regs->ip (e.g. function fault injection)
> must set a dummy post_handler to its kprobes when registering.
> However, if such regs->ip modifying kprobes is set on a function,
> that function can not be livepatched.
>
> Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> ---
> kernel/kprobes.c | 56 +++++++++++++++++++++++++++++++++++++++---------------
> 1 file changed, 40 insertions(+), 16 deletions(-)
>
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 9873fc627d61..29065380dad0 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -961,9 +961,16 @@ static struct kprobe *alloc_aggr_kprobe(struct kprobe *p)
>
> #ifdef CONFIG_KPROBES_ON_FTRACE
> static struct ftrace_ops kprobe_ftrace_ops __read_mostly = {
> + .func = kprobe_ftrace_handler,
> + .flags = FTRACE_OPS_FL_SAVE_REGS,
> +};
> +
> +static struct ftrace_ops kprobe_ipmodify_ops __read_mostly = {
> .func = kprobe_ftrace_handler,
> .flags = FTRACE_OPS_FL_SAVE_REGS | FTRACE_OPS_FL_IPMODIFY,
> };
> +
> +static int kprobe_ipmodify_enabled;
> static int kprobe_ftrace_enabled;
>
> /* Must ensure p->addr is really on ftrace */
> @@ -976,58 +983,75 @@ static int prepare_kprobe(struct kprobe *p)
> }
>
> /* Caller must lock kprobe_mutex */
> -static int arm_kprobe_ftrace(struct kprobe *p)
> +static int __arm_kprobe_ftrace(struct kprobe *p, struct ftrace_ops *ops,
> + int *cnt)
> {
> int ret = 0;
>
> - ret = ftrace_set_filter_ip(&kprobe_ftrace_ops,
> - (unsigned long)p->addr, 0, 0);
> + ret = ftrace_set_filter_ip(ops, (unsigned long)p->addr, 0, 0);
> if (ret) {
> pr_debug("Failed to arm kprobe-ftrace at %pS (%d)\n",
> p->addr, ret);
> return ret;
> }
>
> - if (kprobe_ftrace_enabled == 0) {
> - ret = register_ftrace_function(&kprobe_ftrace_ops);
> + if (*cnt == 0) {
> + ret = register_ftrace_function(ops);
> if (ret) {
> pr_debug("Failed to init kprobe-ftrace (%d)\n", ret);
> goto err_ftrace;
> }
> }
>
> - kprobe_ftrace_enabled++;
> + (*cnt)++;
> return ret;
>
> err_ftrace:
> /*
> - * Note: Since kprobe_ftrace_ops has IPMODIFY set, and ftrace requires a
> - * non-empty filter_hash for IPMODIFY ops, we're safe from an accidental
> - * empty filter_hash which would undesirably trace all functions.
> + * At this point, sinec ops is not registered, we should be sefe from
> + * registering empty filter.
> */
> - ftrace_set_filter_ip(&kprobe_ftrace_ops, (unsigned long)p->addr, 1, 0);
> + ftrace_set_filter_ip(ops, (unsigned long)p->addr, 1, 0);
> return ret;
> }
>
> +static int arm_kprobe_ftrace(struct kprobe *p)
> +{
> + bool ipmodify = (p->post_handler != NULL);
> +
> + return __arm_kprobe_ftrace(p,
> + ipmodify ? &kprobe_ipmodify_ops : &kprobe_ftrace_ops,
> + ipmodify ? &kprobe_ipmodify_enabled : &kprobe_ftrace_enabled);
> +}
> +
> /* Caller must lock kprobe_mutex */
> -static int disarm_kprobe_ftrace(struct kprobe *p)
> +static int __disarm_kprobe_ftrace(struct kprobe *p, struct ftrace_ops *ops,
> + int *cnt)
> {
> int ret = 0;
>
> - if (kprobe_ftrace_enabled == 1) {
> - ret = unregister_ftrace_function(&kprobe_ftrace_ops);
> + if (*cnt == 1) {
> + ret = unregister_ftrace_function(ops);
> if (WARN(ret < 0, "Failed to unregister kprobe-ftrace (%d)\n", ret))
> return ret;
> }
>
> - kprobe_ftrace_enabled--;
> + (*cnt)--;
>
> - ret = ftrace_set_filter_ip(&kprobe_ftrace_ops,
> - (unsigned long)p->addr, 1, 0);
> + ret = ftrace_set_filter_ip(ops, (unsigned long)p->addr, 1, 0);
> WARN_ONCE(ret < 0, "Failed to disarm kprobe-ftrace at %pS (%d)\n",
> p->addr, ret);
> return ret;
> }
> +
> +static int disarm_kprobe_ftrace(struct kprobe *p)
> +{
> + bool ipmodify = (p->post_handler != NULL);
> +
> + return __disarm_kprobe_ftrace(p,
> + ipmodify ? &kprobe_ipmodify_ops : &kprobe_ftrace_ops,
> + ipmodify ? &kprobe_ipmodify_enabled : &kprobe_ftrace_enabled);
> +}
> #else /* !CONFIG_KPROBES_ON_FTRACE */
> #define prepare_kprobe(p) arch_prepare_kprobe(p)
> #define arm_kprobe_ftrace(p) (-ENODEV)
>
Thanks for the quick patch, Masami!
I gave it a spin and here are my new testing results:
perf probe, then livepatch
--------------------------
% perf probe --add cmdline_proc_show
Added new event:
probe:cmdline_proc_show (on cmdline_proc_show)
You can now use it in all perf tools, such as:
perf record -e probe:cmdline_proc_show -aR sleep 1
% perf record -e probe:cmdline_proc_show -aR sleep 30 &
[1] 980
% insmod samples/livepatch/livepatch-sample.ko
% cat /proc/cmdline
this has been live patched
% fg
perf record -e probe:cmdline_proc_show -aR sleep 30
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.177 MB perf.data (2 samples) ]
% perf script
insmod 983 [000] 157.126556: probe:cmdline_proc_show: (ffffffff9bf74890)
cat 985 [000] 162.304028: probe:cmdline_proc_show: (ffffffff9bf74890)
livepatch, then perf probe
--------------------------
% insmod samples/livepatch/livepatch-sample.ko
% cat /proc/cmdline
this has been live patched
% perf record -e probe:cmdline_proc_show -aR sleep 30
event syntax error: 'probe:cmdline_proc_show'
\___ unknown tracepoint
Error: File /sys/kernel/debug/tracing/events/probe/cmdline_proc_show not found.
Hint: Perhaps this kernel misses some CONFIG_ setting to enable this feature?.
Run 'perf list' for a list of valid events
Usage: perf record [<options>] [<command>]
or: perf record [<options>] -- <command> [<options>]
-e, --event <event> event selector. use 'perf list' to list available events
These results reflect my underestanding of FTRACE_OPS_FL_IPMODIFY in
light of your changes, so feel free to add my:
Acked-by: Joe Lawrence <joe.lawrence@...hat.com>
-- Joe
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