From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_NEOMUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 21F86C43441 for ; Mon, 26 Nov 2018 17:56:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D656720663 for ; Mon, 26 Nov 2018 17:56:33 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D656720663 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726881AbeK0EvX (ORCPT ); Mon, 26 Nov 2018 23:51:23 -0500 Received: from mx1.redhat.com ([209.132.183.28]:36898 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726251AbeK0EvW (ORCPT ); Mon, 26 Nov 2018 23:51:22 -0500 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 1D54F80F81; Mon, 26 Nov 2018 17:56:31 +0000 (UTC) Received: from treble (ovpn-121-105.rdu2.redhat.com [10.10.121.105]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 535ED1057076; Mon, 26 Nov 2018 17:56:27 +0000 (UTC) Date: Mon, 26 Nov 2018 11:56:24 -0600 From: Josh Poimboeuf To: Peter Zijlstra Cc: x86@kernel.org, linux-kernel@vger.kernel.org, Ard Biesheuvel , Andy Lutomirski , Steven Rostedt , Ingo Molnar , Thomas Gleixner , Linus Torvalds , Masami Hiramatsu , Jason Baron , Jiri Kosina , David Laight , Borislav Petkov , Julia Cartwright , Jessica Yu , "H. Peter Anvin" Subject: Re: [PATCH v2 4/4] x86/static_call: Add inline static call implementation for x86-64 Message-ID: <20181126175624.bruqfbkngbucpvxr@treble> References: <62188c62f6dda49ca2e20629ee8e5a62a6c0b500.1543200841.git.jpoimboe@redhat.com> <20181126160217.GR2113@hirez.programming.kicks-ass.net> <20181126171036.chcbmb35ygpxziub@treble> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20181126171036.chcbmb35ygpxziub@treble> User-Agent: NeoMutt/20180716 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Mon, 26 Nov 2018 17:56:31 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 26, 2018 at 11:10:36AM -0600, Josh Poimboeuf wrote: > On Mon, Nov 26, 2018 at 05:02:17PM +0100, Peter Zijlstra wrote: > > On Mon, Nov 26, 2018 at 07:55:00AM -0600, Josh Poimboeuf wrote: > > > diff --git a/arch/x86/kernel/static_call.c b/arch/x86/kernel/static_call.c > > > index 8026d176f25c..d3869295b88d 100644 > > > --- a/arch/x86/kernel/static_call.c > > > +++ b/arch/x86/kernel/static_call.c > > > @@ -9,13 +9,21 @@ > > > > > > void static_call_bp_handler(void); > > > void *bp_handler_dest; > > > +void *bp_handler_continue; > > > > > > asm(".pushsection .text, \"ax\" \n" > > > ".globl static_call_bp_handler \n" > > > ".type static_call_bp_handler, @function \n" > > > "static_call_bp_handler: \n" > > > - "ANNOTATE_RETPOLINE_SAFE \n" > > > +#ifdef CONFIG_HAVE_STATIC_CALL_INLINE > > > + ANNOTATE_RETPOLINE_SAFE > > > + "call *bp_handler_dest \n" > > > + ANNOTATE_RETPOLINE_SAFE > > > + "jmp *bp_handler_continue \n" > > > +#else /* !CONFIG_HAVE_STATIC_CALL_INLINE */ > > > + ANNOTATE_RETPOLINE_SAFE > > > "jmp *bp_handler_dest \n" > > > +#endif > > > ".popsection \n"); > > > > > > void arch_static_call_transform(void *site, void *tramp, void *func) > > > @@ -25,7 +33,10 @@ void arch_static_call_transform(void *site, void *tramp, void *func) > > > unsigned char insn_opcode; > > > unsigned char opcodes[CALL_INSN_SIZE]; > > > > > > - insn = (unsigned long)tramp; > > > + if (IS_ENABLED(CONFIG_HAVE_STATIC_CALL_INLINE)) > > > + insn = (unsigned long)site; > > > + else > > > + insn = (unsigned long)tramp; > > > > > > mutex_lock(&text_mutex); > > > > > > @@ -41,8 +52,10 @@ void arch_static_call_transform(void *site, void *tramp, void *func) > > > opcodes[0] = insn_opcode; > > > memcpy(&opcodes[1], &dest_relative, CALL_INSN_SIZE - 1); > > > > > > - /* Set up the variable for the breakpoint handler: */ > > > + /* Set up the variables for the breakpoint handler: */ > > > bp_handler_dest = func; > > > + if (IS_ENABLED(CONFIG_HAVE_STATIC_CALL_INLINE)) > > > + bp_handler_continue = (void *)(insn + CALL_INSN_SIZE); > > > > > > /* Patch the call site: */ > > > text_poke_bp((void *)insn, opcodes, CALL_INSN_SIZE, > > > > OK, so this is where that static_call_bp_handler comes from; you need > > that CALL to frob the stack. > > > > But I still think it is broken; consider: > > > > CPU0 CPU1 > > > > bp_handler = ponies; > > > > text_poke_bp(, &static_call_bp_handler) > > text_poke(&int3); > > on_each_cpu(sync) > > > > ... > > > > > > text_poke(/* all but first bytes */) > > on_each_cpu(sync) > > > > ... > > > > > > > > pt_regs->ip = &static_call_bp_handler > > > > > > // VCPU takes a nap... > > text_poke(/* first byte */) > > on_each_cpu(sync) > > > > ... > > > > > > // VCPU sleeps more > > bp_handler = unicorn; > > > > CALL unicorn > > > > *whoops* > > > > Now, granted, that is all rather 'unlikely', but that never stopped > > Murphy. > > Good find, thanks Peter. > > As we discussed on IRC, we'll need to fix this from within the int3 > exception handler by faking the call: putting a fake return address on > the stack (pointing to right after the call) and setting regs->ip to the > called function. > > And for the out-of-line case we can just jump straight to the function, > so the function itself will be the text_poke_bp() "handler". > > So the static_call_bp_handler() trampoline will go away. Peter suggested updating the text_poke_bp() interface to add a handler which is called from int3 context. This seems to work. diff --git a/arch/x86/include/asm/text-patching.h b/arch/x86/include/asm/text-patching.h index e85ff65c43c3..7fcaa37c1876 100644 --- a/arch/x86/include/asm/text-patching.h +++ b/arch/x86/include/asm/text-patching.h @@ -20,6 +20,8 @@ static inline void apply_paravirt(struct paravirt_patch_site *start, extern void *text_poke_early(void *addr, const void *opcode, size_t len); +typedef void (*bp_handler_t)(struct pt_regs *regs); + /* * Clear and restore the kernel write-protection flag on the local CPU. * Allows the kernel to edit read-only pages. @@ -36,7 +38,8 @@ extern void *text_poke_early(void *addr, const void *opcode, size_t len); */ extern void *text_poke(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, void *handler); +extern void *text_poke_bp(void *addr, const void *opcode, size_t len, + bp_handler_t handler, void *resume); extern int after_bootmem; #endif /* _ASM_X86_TEXT_PATCHING_H */ diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index ebeac487a20c..b6fb645488be 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -738,7 +738,8 @@ static void do_sync_core(void *info) } static bool bp_patching_in_progress; -static void *bp_int3_handler, *bp_int3_addr; +static void *bp_int3_resume, *bp_int3_addr; +static bp_handler_t bp_int3_handler; int poke_int3_handler(struct pt_regs *regs) { @@ -746,11 +747,11 @@ int poke_int3_handler(struct pt_regs *regs) * Having observed our INT3 instruction, we now must observe * bp_patching_in_progress. * - * in_progress = TRUE INT3 - * WMB RMB - * write INT3 if (in_progress) + * in_progress = TRUE INT3 + * WMB RMB + * write INT3 if (in_progress) * - * Idem for bp_int3_handler. + * Idem for bp_int3_resume. */ smp_rmb(); @@ -760,8 +761,10 @@ int poke_int3_handler(struct pt_regs *regs) if (user_mode(regs) || regs->ip != (unsigned long)bp_int3_addr) return 0; - /* set up the specified breakpoint handler */ - regs->ip = (unsigned long) bp_int3_handler; + if (bp_int3_handler) + bp_int3_handler(regs); + + regs->ip = (unsigned long)bp_int3_resume; return 1; @@ -772,7 +775,8 @@ int poke_int3_handler(struct pt_regs *regs) * @addr: address to patch * @opcode: opcode of new instruction * @len: length to copy - * @handler: address to jump to when the temporary breakpoint is hit + * @handler: handler to call from int3 context (optional) + * @resume: address to jump to when returning from int3 context * * Modify multi-byte instruction by using int3 breakpoint on SMP. * We completely avoid stop_machine() here, and achieve the @@ -787,11 +791,13 @@ int poke_int3_handler(struct pt_regs *regs) * replacing opcode * - sync cores */ -void *text_poke_bp(void *addr, const void *opcode, size_t len, void *handler) +void *text_poke_bp(void *addr, const void *opcode, size_t len, + bp_handler_t handler, void *resume) { unsigned char int3 = 0xcc; bp_int3_handler = handler; + bp_int3_resume = resume; bp_int3_addr = (u8 *)addr + sizeof(int3); bp_patching_in_progress = true; diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c index aac0c1f7e354..1a54c5c6d9f3 100644 --- a/arch/x86/kernel/jump_label.c +++ b/arch/x86/kernel/jump_label.c @@ -90,7 +90,7 @@ static void __ref __jump_label_transform(struct jump_entry *entry, return; } - text_poke_bp((void *)jump_entry_code(entry), code, JUMP_LABEL_NOP_SIZE, + text_poke_bp((void *)jump_entry_code(entry), code, JUMP_LABEL_NOP_SIZE, NULL, (void *)jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE); } diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c index 40b16b270656..5787f48be243 100644 --- a/arch/x86/kernel/kprobes/opt.c +++ b/arch/x86/kernel/kprobes/opt.c @@ -446,7 +446,7 @@ void arch_optimize_kprobes(struct list_head *oplist) insn_buf[0] = RELATIVEJUMP_OPCODE; *(s32 *)(&insn_buf[1]) = rel; - text_poke_bp(op->kp.addr, insn_buf, RELATIVEJUMP_SIZE, + text_poke_bp(op->kp.addr, insn_buf, RELATIVEJUMP_SIZE, NULL, op->optinsn.insn); list_del_init(&op->list); @@ -461,7 +461,7 @@ void arch_unoptimize_kprobe(struct optimized_kprobe *op) /* Set int3 to first byte for kprobes */ insn_buf[0] = BREAKPOINT_INSTRUCTION; memcpy(insn_buf + 1, op->optinsn.copied_insn, RELATIVE_ADDR_SIZE); - text_poke_bp(op->kp.addr, insn_buf, RELATIVEJUMP_SIZE, + text_poke_bp(op->kp.addr, insn_buf, RELATIVEJUMP_SIZE, NULL, op->optinsn.insn); } diff --git a/arch/x86/kernel/static_call.c b/arch/x86/kernel/static_call.c index d3869295b88d..8fd6c8556750 100644 --- a/arch/x86/kernel/static_call.c +++ b/arch/x86/kernel/static_call.c @@ -7,24 +7,19 @@ #define CALL_INSN_SIZE 5 -void static_call_bp_handler(void); -void *bp_handler_dest; -void *bp_handler_continue; +unsigned long bp_handler_call_return_addr; -asm(".pushsection .text, \"ax\" \n" - ".globl static_call_bp_handler \n" - ".type static_call_bp_handler, @function \n" - "static_call_bp_handler: \n" +static void static_call_bp_handler(struct pt_regs *regs) +{ #ifdef CONFIG_HAVE_STATIC_CALL_INLINE - ANNOTATE_RETPOLINE_SAFE - "call *bp_handler_dest \n" - ANNOTATE_RETPOLINE_SAFE - "jmp *bp_handler_continue \n" -#else /* !CONFIG_HAVE_STATIC_CALL_INLINE */ - ANNOTATE_RETPOLINE_SAFE - "jmp *bp_handler_dest \n" + /* + * Push the return address on the stack so the "called" function will + * return to immediately after the call site. + */ + regs->sp -= sizeof(long); + *(unsigned long *)regs->sp = bp_handler_call_return_addr; #endif - ".popsection \n"); +} void arch_static_call_transform(void *site, void *tramp, void *func) { @@ -52,14 +47,12 @@ void arch_static_call_transform(void *site, void *tramp, void *func) opcodes[0] = insn_opcode; memcpy(&opcodes[1], &dest_relative, CALL_INSN_SIZE - 1); - /* Set up the variables for the breakpoint handler: */ - bp_handler_dest = func; if (IS_ENABLED(CONFIG_HAVE_STATIC_CALL_INLINE)) - bp_handler_continue = (void *)(insn + CALL_INSN_SIZE); + bp_handler_call_return_addr = insn + CALL_INSN_SIZE; /* Patch the call site: */ text_poke_bp((void *)insn, opcodes, CALL_INSN_SIZE, - static_call_bp_handler); + static_call_bp_handler, func); done: mutex_unlock(&text_mutex);