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Date: Mon, 13 Jul 2020 08:05:49 +0300 From: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com> To: Peter Zijlstra <peterz@...radead.org> Cc: linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>, "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>, Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>, "David S. Miller" <davem@...emloft.net>, Masami Hiramatsu <mhiramat@...nel.org>, Steven Rostedt <rostedt@...dmis.org>, Andrew Morton <akpm@...ux-foundation.org>, "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>, Will Deacon <will@...nel.org>, Kees Cook <keescook@...omium.org>, Arnd Bergmann <arnd@...db.de>, Alexandre Ghiti <alex@...ti.fr>, Masahiro Yamada <masahiroy@...nel.org>, Sami Tolvanen <samitolvanen@...gle.com>, Peter Collingbourne <pcc@...gle.com>, Krzysztof Kozlowski <krzk@...nel.org>, Frederic Weisbecker <frederic@...nel.org>, Stephen Boyd <sboyd@...nel.org>, Alexei Starovoitov <ast@...nel.org>, Mike Rapoport <rppt@...ux.ibm.com>, Sean Christopherson <sean.j.christopherson@...el.com>, Jiri Olsa <jolsa@...hat.com> Subject: Re: [PATCH RFC] kprobes: Remove MODULES dependency On Fri, Jul 10, 2020 at 12:49:10PM +0200, Peter Zijlstra wrote: > On Fri, Jul 10, 2020 at 01:36:38PM +0300, Jarkko Sakkinen wrote: > > Just so that I know (and learn), what did exactly disable optprobes? > > So regular, old-skool style kprobe is: > > - copy original instruction out > - replace instruction with breakpoint (int3 on x86) > - have exception handler return to the copied instruction with > single-step on > - have single step exception handler return to the original > instruction stream > > which is 2 exceptions. Out of pure interest, how does it handle a jump (as the original opcode), given that it single steps a copy? > optprobes avoid the single-step by not only writing a single > instruction, but additionally placing a JMP instruction behind it such > that it will automagically continue in the original instruction stream. > > This brings the requirement that the copied instruction is placed > within the JMP displacement of the regular kernel text (s32 on x86). > > module_alloc() ensures the memory provided is within that range. Right, a relative jump is placed instead of 0xcc to the breakpoint? /Jarkko
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