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[95.82.160.96]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-5f36f069dedsm3810613a12.41.2025.04.13.12.05.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 13 Apr 2025 12:05:34 -0700 (PDT) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Sun, 13 Apr 2025 21:05:29 +0200 To: Oleg Nesterov Cc: Andrii Nakryiko , Peter Zijlstra , Ingo Molnar , Andrii Nakryiko , bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, x86@kernel.org, Song Liu , Yonghong Song , John Fastabend , Hao Luo , Steven Rostedt , Masami Hiramatsu , Alan Maguire Subject: Re: [PATCHv2 perf/core 1/2] uprobes/x86: Add support to emulate nop instructions Message-ID: References: <20250411121756.567274-1-jolsa@kernel.org> <20250411163242.GI5322@redhat.com> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250411163242.GI5322@redhat.com> On Fri, Apr 11, 2025 at 06:32:43PM +0200, Oleg Nesterov wrote: > On 04/11, Andrii Nakryiko wrote: > > > > > --- a/arch/x86/kernel/uprobes.c > > > +++ b/arch/x86/kernel/uprobes.c > > > @@ -840,6 +840,12 @@ static int branch_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn) > > > insn_byte_t p; > > > int i; > > > > > > + /* x86_nops[i]; same as jmp with .offs = 0 */ > > > + for (i = 1; i <= ASM_NOP_MAX; ++i) { > > > > i <= ASM_NOP_MAX && i <= insn->length > > > > ? > > > > otherwise what prevents us from reading past the actual instruction bytes? > > Well, copy_insn() just copies MAX_UINSN_BYTES into arch_uprobe.insn[]. > If, say, the 1st 11 bytes of arch_uprobe.insn (or insn->kaddr) match > x86_nops[11] then insn->length must be 11, or insn_decode() is buggy? > > > or, actually, shouldn't we just check memcmp(x86_nops[insn->length]) > > if insn->length < ASM_NOP_MAX ? nice, did not think of that > > Hmm... agreed. > > Either way this check can't (doesn't even try to) detect, say, > "rep; BYTES_NOP5", so we do not care if insn->length == 6 in this case. > > Good point! I'll run tests and send formal patch for change below thanks, jirka --- diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c index 9194695662b2..6d383839e839 100644 --- a/arch/x86/kernel/uprobes.c +++ b/arch/x86/kernel/uprobes.c @@ -840,6 +840,11 @@ static int branch_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn) insn_byte_t p; int i; + /* x86_nops[insn->length]; same as jmp with .offs = 0 */ + if (insn->length <= ASM_NOP_MAX && + !memcmp(insn->kaddr, x86_nops[insn->length], insn->length)) + goto setup; + switch (opc1) { case 0xeb: /* jmp 8 */ case 0xe9: /* jmp 32 */