From: Masami Hiramatsu <mhiramat@kernel.org> To: Peter Zijlstra <peterz@infradead.org> Cc: x86@kernel.org, linux-kernel@vger.kernel.org, rostedt@goodmis.org, mhiramat@kernel.org, bristot@redhat.com, jbaron@akamai.com, torvalds@linux-foundation.org, tglx@linutronix.de, mingo@kernel.org, namit@vmware.com, hpa@zytor.com, luto@kernel.org, ard.biesheuvel@linaro.org, jpoimboe@redhat.com, jeyu@kernel.org, paulmck@kernel.org, mathieu.desnoyers@efficios.com Subject: Re: [PATCH v4 12/16] x86/kprobes: Fix ordering Date: Tue, 22 Oct 2019 10:35:21 +0900 [thread overview] Message-ID: <20191022103521.3015bc5e128cd68fa645013c@kernel.org> (raw) In-Reply-To: <20191018074634.629386219@infradead.org> On Fri, 18 Oct 2019 09:35:37 +0200 Peter Zijlstra <peterz@infradead.org> wrote: > Kprobes does something like: > > register: > arch_arm_kprobe() > text_poke(INT3) > /* guarantees nothing, INT3 will become visible at some point, maybe */ > > kprobe_optimizer() > /* guarantees the bytes after INT3 are unused */ > syncrhonize_rcu_tasks(); > text_poke_bp(JMP32); > /* implies IPI-sync, kprobe really is enabled */ > > > unregister: > __disarm_kprobe() > unoptimize_kprobe() > text_poke_bp(INT3 + tail); > /* implies IPI-sync, so tail is guaranteed visible */ > arch_disarm_kprobe() > text_poke(old); > /* guarantees nothing, old will maybe become visible */ > > synchronize_rcu() > > free-stuff Note that this is only for the case of optimized kprobe. (On some probe points we can not optimize it) > > Now the problem is that on register, the synchronize_rcu_tasks() does > not imply sufficient to guarantee all CPUs have already observed INT3 > (although in practise this is exceedingly unlikely not to have > happened) (similar to how MEMBARRIER_CMD_PRIVATE_EXPEDITED does not > imply MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE). OK, so the sync_core() after int3 is needed to guarantee the probe is enabled on each core. > > Worse, even if it did, we'd have to do 2 synchronize calls to provide > the guarantee we're looking for, the first to ensure INT3 is visible, > the second to guarantee nobody is then still using the instruction > bytes after INT3. I think this 2nd guarantee is done by syncrhonize_rcu() if we put sync_core() after int3. syncrhonize_rcu() ensures that all cores once scheduled and all interrupts have done. > > Similar on unregister; the synchronize_rcu() between > __unregister_kprobe_top() and __unregister_kprobe_bottom() does not > guarantee all CPUs are free of the INT3 (and observe the old text). I agree with putting sync_core() after putting/removing INT3. > > Therefore, sprinkle some IPI-sync love around. This guarantees that > all CPUs agree on the text and RCU once again provides the required > guaranteed. > > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > Cc: hpa@zytor.com > Cc: paulmck@kernel.org > Cc: mathieu.desnoyers@efficios.com > --- > arch/x86/include/asm/text-patching.h | 1 + > arch/x86/kernel/alternative.c | 11 ++++++++--- > arch/x86/kernel/kprobes/core.c | 2 ++ > arch/x86/kernel/kprobes/opt.c | 12 ++++-------- > 4 files changed, 15 insertions(+), 11 deletions(-) > > --- a/arch/x86/include/asm/text-patching.h > +++ b/arch/x86/include/asm/text-patching.h > @@ -42,6 +42,7 @@ extern void text_poke_early(void *addr, > * an inconsistent instruction while you patch. > */ > extern void *text_poke(void *addr, const void *opcode, size_t len); > +extern void text_poke_sync(void); > extern void *text_poke_kgdb(void *addr, const void *opcode, size_t len); > extern int poke_int3_handler(struct pt_regs *regs); > extern void text_poke_bp(void *addr, const void *opcode, size_t len, const void *emulate); > --- a/arch/x86/kernel/alternative.c > +++ b/arch/x86/kernel/alternative.c > @@ -936,6 +936,11 @@ static void do_sync_core(void *info) > sync_core(); > } > > +void text_poke_sync(void) > +{ > + on_each_cpu(do_sync_core, NULL, 1); > +} > + > struct text_poke_loc { > s32 rel_addr; /* addr := _stext + rel_addr */ > s32 rel32; > @@ -1085,7 +1090,7 @@ static void text_poke_bp_batch(struct te > for (i = 0; i < nr_entries; i++) > text_poke(text_poke_addr(&tp[i]), &int3, sizeof(int3)); > > - on_each_cpu(do_sync_core, NULL, 1); > + text_poke_sync(); > > /* > * Second step: update all but the first byte of the patched range. > @@ -1107,7 +1112,7 @@ static void text_poke_bp_batch(struct te > * not necessary and we'd be safe even without it. But > * better safe than sorry (plus there's not only Intel). > */ > - on_each_cpu(do_sync_core, NULL, 1); > + text_poke_sync(); > } > > /* > @@ -1123,7 +1128,7 @@ static void text_poke_bp_batch(struct te > } > > if (do_sync) > - on_each_cpu(do_sync_core, NULL, 1); > + text_poke_sync(); > > /* > * sync_core() implies an smp_mb() and orders this store against > --- a/arch/x86/kernel/kprobes/core.c > +++ b/arch/x86/kernel/kprobes/core.c > @@ -502,11 +502,13 @@ int arch_prepare_kprobe(struct kprobe *p > void arch_arm_kprobe(struct kprobe *p) > { > text_poke(p->addr, ((unsigned char []){INT3_INSN_OPCODE}), 1); > + text_poke_sync(); > } > > void arch_disarm_kprobe(struct kprobe *p) > { > text_poke(p->addr, &p->opcode, 1); > + text_poke_sync(); > } This looks good to me. > > void arch_remove_kprobe(struct kprobe *p) > --- a/arch/x86/kernel/kprobes/opt.c > +++ b/arch/x86/kernel/kprobes/opt.c > @@ -444,14 +444,10 @@ void arch_optimize_kprobes(struct list_h > /* Replace a relative jump with a breakpoint (int3). */ > void arch_unoptimize_kprobe(struct optimized_kprobe *op) > { > - u8 insn_buff[JMP32_INSN_SIZE]; > - > - /* Set int3 to first byte for kprobes */ > - insn_buff[0] = INT3_INSN_OPCODE; > - memcpy(insn_buff + 1, op->optinsn.copied_insn, DISP32_SIZE); > - > - text_poke_bp(op->kp.addr, insn_buff, JMP32_INSN_SIZE, > - text_gen_insn(JMP32_INSN_OPCODE, op->kp.addr, op->optinsn.insn)); > + arch_arm_kprobe(&op->kp); > + text_poke(op->kp.addr + INT3_INSN_SIZE, > + op->optinsn.copied_insn, DISP32_SIZE); > + text_poke_sync(); > } For this part, I thought it was same as what text_poke_bp() does. But, indeed, this looks better (simpler & lighter) than using text_poke_bp()... So, in total, this looks good to me. Acked-by: Masami Hiramatsu <mhiramat@kernel.org> Thank you, -- Masami Hiramatsu <mhiramat@kernel.org>
next prev parent reply other threads:[~2019-10-22 1:35 UTC|newest] Thread overview: 70+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-10-18 7:35 [PATCH v4 00/16] Rewrite x86/ftrace to use text_poke (and more) Peter Zijlstra 2019-10-18 7:35 ` [PATCH v4 01/16] x86/alternatives: Teach text_poke_bp() to emulate instructions Peter Zijlstra 2019-10-18 7:35 ` [PATCH v4 02/16] x86/alternatives: Update int3_emulate_push() comment Peter Zijlstra 2019-10-18 7:35 ` [PATCH v4 03/16] x86/alternatives,jump_label: Provide better text_poke() batching interface Peter Zijlstra 2019-10-21 8:48 ` Ingo Molnar 2019-10-21 9:21 ` Peter Zijlstra 2019-10-18 7:35 ` [PATCH v4 04/16] x86/alternatives: Add and use text_gen_insn() helper Peter Zijlstra 2019-10-18 7:35 ` [PATCH v4 05/16] x86/ftrace: Use text_poke() Peter Zijlstra 2019-10-18 7:35 ` [PATCH v4 06/16] x86/mm: Remove set_kernel_text_r[ow]() Peter Zijlstra 2019-10-18 7:35 ` [PATCH v4 07/16] x86/alternative: Add text_opcode_size() Peter Zijlstra 2019-10-18 7:35 ` [PATCH v4 08/16] x86/ftrace: Use text_gen_insn() Peter Zijlstra 2019-10-18 7:35 ` [PATCH v4 09/16] x86/alternative: Remove text_poke_loc::len Peter Zijlstra 2019-10-21 8:58 ` Ingo Molnar 2019-10-21 9:02 ` Ingo Molnar 2019-10-18 7:35 ` [PATCH v4 10/16] x86/alternative: Shrink text_poke_loc Peter Zijlstra 2019-10-21 9:01 ` Ingo Molnar 2019-10-21 9:25 ` Peter Zijlstra 2019-10-21 9:33 ` Ingo Molnar 2019-10-18 7:35 ` [PATCH v4 11/16] x86/kprobes: Convert to text-patching.h Peter Zijlstra 2019-10-21 14:57 ` Masami Hiramatsu 2019-10-18 7:35 ` [PATCH v4 12/16] x86/kprobes: Fix ordering Peter Zijlstra 2019-10-22 1:35 ` Masami Hiramatsu [this message] 2019-10-22 10:31 ` Peter Zijlstra 2019-10-18 7:35 ` [PATCH v4 13/16] arm/ftrace: Use __patch_text_real() Peter Zijlstra 2019-10-28 16:25 ` Will Deacon 2019-10-28 16:34 ` Peter Zijlstra 2019-10-28 16:35 ` Peter Zijlstra 2019-10-28 16:47 ` Will Deacon 2019-10-28 16:55 ` Peter Zijlstra 2019-10-18 7:35 ` [PATCH v4 14/16] module: Remove set_all_modules_text_*() Peter Zijlstra 2019-10-18 7:35 ` [PATCH v4 15/16] module: Move where we mark modules RO,X Peter Zijlstra 2019-10-21 13:53 ` Josh Poimboeuf 2019-10-21 14:14 ` Peter Zijlstra 2019-10-21 15:34 ` Peter Zijlstra 2019-10-21 15:44 ` Peter Zijlstra 2019-10-21 16:11 ` Peter Zijlstra 2019-10-22 11:31 ` Heiko Carstens 2019-10-22 12:31 ` Peter Zijlstra 2019-10-23 11:48 ` Peter Zijlstra 2019-10-23 15:16 ` Peter Zijlstra 2019-10-23 17:15 ` Josh Poimboeuf 2019-10-24 10:59 ` Peter Zijlstra 2019-10-24 18:31 ` Josh Poimboeuf 2019-10-24 20:33 ` Peter Zijlstra 2019-10-23 17:00 ` Josh Poimboeuf 2019-10-24 13:16 ` Peter Zijlstra 2019-10-25 6:44 ` Petr Mladek 2019-10-25 8:43 ` Peter Zijlstra 2019-10-25 10:06 ` Peter Zijlstra 2019-10-25 13:50 ` Josh Poimboeuf 2019-10-26 1:17 ` Josh Poimboeuf 2019-10-28 10:07 ` Peter Zijlstra 2019-10-28 10:43 ` Peter Zijlstra 2019-10-25 9:16 ` Peter Zijlstra 2019-10-22 2:21 ` Steven Rostedt 2019-10-22 20:24 ` Peter Zijlstra 2019-10-22 20:40 ` Steven Rostedt 2019-10-23 9:07 ` Peter Zijlstra 2019-10-23 18:52 ` Steven Rostedt 2019-10-24 10:16 ` Peter Zijlstra 2019-10-24 10:18 ` Peter Zijlstra 2019-10-24 15:00 ` Steven Rostedt 2019-10-24 16:43 ` Peter Zijlstra 2019-10-24 18:17 ` Steven Rostedt 2019-10-24 20:24 ` Peter Zijlstra 2019-10-24 20:28 ` Steven Rostedt 2019-10-18 7:35 ` [PATCH v4 16/16] ftrace: Merge ftrace_module_{init,enable}() Peter Zijlstra 2019-10-18 8:20 ` Peter Zijlstra 2019-10-21 9:09 ` [PATCH v4 00/16] Rewrite x86/ftrace to use text_poke (and more) Ingo Molnar 2019-10-21 13:38 ` Steven Rostedt
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