From: Nick Desaulniers <ndesaulniers@google.com> To: Mark Rutland <mark.rutland@arm.com> Cc: madvenka@linux.microsoft.com, jpoimboe@redhat.com, peterz@infradead.org, chenzhongjin@huawei.com, broonie@kernel.org, nobuta.keiya@fujitsu.com, sjitindarsingh@gmail.com, catalin.marinas@arm.com, will@kernel.org, jamorris@linux.microsoft.com, linux-arm-kernel@lists.infradead.org, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev, linux-toolchains@vger.kernel.org Subject: Re: [RFC PATCH v3 00/22] arm64: livepatch: Use ORC for dynamic frame pointer validation Date: Thu, 13 Apr 2023 10:04:05 -0700 [thread overview] Message-ID: <ZDg2BUL4uauG/w4T@google.com> (raw) In-Reply-To: <ZByJmnc/XDcqQwoZ@FVFF77S0Q05N.cambridge.arm.com> On Thu, Mar 23, 2023 at 05:17:14PM +0000, Mark Rutland wrote: > Hi Madhavan, > > At a high-level, I think this still falls afoul of our desire to not reverse > engineer control flow from the binary, and so I do not think this is the right > approach. I've expanded a bit on that below. > > I do think it would be nice to have *some* of the objtool changes, as I do > think we will want to use objtool for some things in future (e.g. some > build-time binary patching such as table sorting). > > > Problem > > ======= > > > > Objtool is complex and highly architecture-dependent. There are a lot of > > different checks in objtool that all of the code in the kernel must pass > > before livepatch can be enabled. If a check fails, it must be corrected > > before we can proceed. Sometimes, the kernel code needs to be fixed. > > Sometimes, it is a compiler bug that needs to be fixed. The challenge is > > also to prove that all the work is complete for an architecture. > > > > As such, it presents a great challenge to enable livepatch for an > > architecture. > > There's a more fundamental issue here in that objtool has to reverse-engineer > control flow, and so even if the kernel code and compiled code generation is > *perfect*, it's possible that objtool won't recognise the structure of the > generated code, and won't be able to reverse-engineer the correct control flow. > > We've seen issues where objtool didn't understand jump tables, so support for > that got disabled on x86. A key objection from the arm64 side is that we don't > want to disable compile code generation strategies like this. Further, as > compiles evolve, their code generation strategies will change, and it's likely > there will be other cases that crop up. This is inherently fragile. > > The key objections from the arm64 side is that we don't want to > reverse-engineer details from the binary, as this is complex, fragile, and > unstable. This is why we've previously suggested that we should work with > compiler folk to get what we need. > This still requires reverse-engineering the forward-edge control flow in order > to compute those offets, so the same objections apply with this approach. I do > not think this is the right approach. > > I would *strongly* prefer that we work with compiler folk to get the > information that we need. IDK if it's relevant here, but I did see a commit go by to LLVM that seemed to include such info in a custom ELF section (for the purposes of improving fuzzing, IIUC). Maybe such an encoding scheme could be tested to see if it's reliable or usable? - https://github.com/llvm/llvm-project/commit/3e52c0926c22575d918e7ca8369522b986635cd3 - https://clang.llvm.org/docs/SanitizerCoverage.html#tracing-control-flow > > [...] > > > FWIW, I have also compared the CFI I am generating with DWARF > > information that the compiler generates. The CFIs match a > > 100% for Clang. In the case of gcc, the comparison fails > > in 1.7% of the cases. I have analyzed those cases and found > > the DWARF information generated by gcc is incorrect. The > > ORC generated by my Objtool is correct. > > > Have you reported this to the GCC folk, and can you give any examples? > I'm sure they would be interested in fixing this, regardless of whether we end > up using it. Yeah, at least a bug report is good. "See something, say something."
WARNING: multiple messages have this Message-ID (diff)
From: Nick Desaulniers <ndesaulniers@google.com> To: Mark Rutland <mark.rutland@arm.com> Cc: madvenka@linux.microsoft.com, jpoimboe@redhat.com, peterz@infradead.org, chenzhongjin@huawei.com, broonie@kernel.org, nobuta.keiya@fujitsu.com, sjitindarsingh@gmail.com, catalin.marinas@arm.com, will@kernel.org, jamorris@linux.microsoft.com, linux-arm-kernel@lists.infradead.org, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev, linux-toolchains@vger.kernel.org Subject: Re: [RFC PATCH v3 00/22] arm64: livepatch: Use ORC for dynamic frame pointer validation Date: Thu, 13 Apr 2023 10:04:05 -0700 [thread overview] Message-ID: <ZDg2BUL4uauG/w4T@google.com> (raw) In-Reply-To: <ZByJmnc/XDcqQwoZ@FVFF77S0Q05N.cambridge.arm.com> On Thu, Mar 23, 2023 at 05:17:14PM +0000, Mark Rutland wrote: > Hi Madhavan, > > At a high-level, I think this still falls afoul of our desire to not reverse > engineer control flow from the binary, and so I do not think this is the right > approach. I've expanded a bit on that below. > > I do think it would be nice to have *some* of the objtool changes, as I do > think we will want to use objtool for some things in future (e.g. some > build-time binary patching such as table sorting). > > > Problem > > ======= > > > > Objtool is complex and highly architecture-dependent. There are a lot of > > different checks in objtool that all of the code in the kernel must pass > > before livepatch can be enabled. If a check fails, it must be corrected > > before we can proceed. Sometimes, the kernel code needs to be fixed. > > Sometimes, it is a compiler bug that needs to be fixed. The challenge is > > also to prove that all the work is complete for an architecture. > > > > As such, it presents a great challenge to enable livepatch for an > > architecture. > > There's a more fundamental issue here in that objtool has to reverse-engineer > control flow, and so even if the kernel code and compiled code generation is > *perfect*, it's possible that objtool won't recognise the structure of the > generated code, and won't be able to reverse-engineer the correct control flow. > > We've seen issues where objtool didn't understand jump tables, so support for > that got disabled on x86. A key objection from the arm64 side is that we don't > want to disable compile code generation strategies like this. Further, as > compiles evolve, their code generation strategies will change, and it's likely > there will be other cases that crop up. This is inherently fragile. > > The key objections from the arm64 side is that we don't want to > reverse-engineer details from the binary, as this is complex, fragile, and > unstable. This is why we've previously suggested that we should work with > compiler folk to get what we need. > This still requires reverse-engineering the forward-edge control flow in order > to compute those offets, so the same objections apply with this approach. I do > not think this is the right approach. > > I would *strongly* prefer that we work with compiler folk to get the > information that we need. IDK if it's relevant here, but I did see a commit go by to LLVM that seemed to include such info in a custom ELF section (for the purposes of improving fuzzing, IIUC). Maybe such an encoding scheme could be tested to see if it's reliable or usable? - https://github.com/llvm/llvm-project/commit/3e52c0926c22575d918e7ca8369522b986635cd3 - https://clang.llvm.org/docs/SanitizerCoverage.html#tracing-control-flow > > [...] > > > FWIW, I have also compared the CFI I am generating with DWARF > > information that the compiler generates. The CFIs match a > > 100% for Clang. In the case of gcc, the comparison fails > > in 1.7% of the cases. I have analyzed those cases and found > > the DWARF information generated by gcc is incorrect. The > > ORC generated by my Objtool is correct. > > > Have you reported this to the GCC folk, and can you give any examples? > I'm sure they would be interested in fixing this, regardless of whether we end > up using it. Yeah, at least a bug report is good. "See something, say something." _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2023-04-13 17:04 UTC|newest] Thread overview: 113+ messages / expand[flat|nested] mbox.gz Atom feed top [not found] <0337266cf19f4c98388e3f6d09f590d9de258dc7> 2023-02-02 7:40 ` [RFC PATCH v3 00/22] arm64: livepatch: Use ORC for dynamic frame pointer validation madvenka 2023-02-02 7:40 ` madvenka 2023-02-02 7:40 ` [RFC PATCH v3 01/22] objtool: Reorganize CFI code madvenka 2023-02-02 7:40 ` madvenka 2023-02-02 7:40 ` [RFC PATCH v3 02/22] objtool: Reorganize instruction-related code madvenka 2023-02-02 7:40 ` madvenka 2023-02-02 7:40 ` [RFC PATCH v3 03/22] objtool: Move decode_instructions() to a separate file madvenka 2023-02-02 7:40 ` madvenka 2023-02-02 7:40 ` [RFC PATCH v3 04/22] objtool: Reorganize Unwind hint code madvenka 2023-02-02 7:40 ` madvenka 2023-02-02 7:40 ` [RFC PATCH v3 05/22] objtool: Reorganize ORC types madvenka 2023-02-02 7:40 ` madvenka 2023-02-18 9:30 ` Suraj Jitindar Singh 2023-02-18 9:30 ` Suraj Jitindar Singh 2023-03-06 16:45 ` Madhavan T. Venkataraman 2023-03-06 16:45 ` Madhavan T. Venkataraman 2023-02-02 7:40 ` [RFC PATCH v3 06/22] objtool: Reorganize ORC code madvenka 2023-02-02 7:40 ` madvenka 2023-02-02 7:40 ` [RFC PATCH v3 07/22] objtool: Reorganize ORC kernel code madvenka 2023-02-02 7:40 ` madvenka 2023-02-02 7:40 ` [RFC PATCH v3 08/22] objtool: Introduce STATIC_CHECK madvenka 2023-02-02 7:40 ` madvenka 2023-02-02 7:40 ` [RFC PATCH v3 09/22] objtool: arm64: Add basic definitions and compile madvenka 2023-02-02 7:40 ` madvenka 2023-02-02 7:40 ` [RFC PATCH v3 10/22] objtool: arm64: Implement decoder for Dynamic FP validation madvenka 2023-02-02 7:40 ` madvenka 2023-02-02 7:40 ` [RFC PATCH v3 11/22] objtool: arm64: Invoke the decoder madvenka 2023-02-02 7:40 ` madvenka 2023-02-02 7:40 ` [RFC PATCH v3 12/22] objtool: arm64: Compute destinations for call and jump instructions madvenka 2023-02-02 7:40 ` madvenka 2023-02-02 7:40 ` [RFC PATCH v3 13/22] objtool: arm64: Walk instructions and compute CFI for each instruction madvenka 2023-02-02 7:40 ` madvenka 2023-02-02 7:40 ` [RFC PATCH v3 14/22] objtool: arm64: Generate ORC data from CFI for object files madvenka 2023-02-02 7:40 ` madvenka 2023-02-02 7:40 ` [RFC PATCH v3 15/22] objtool: arm64: Add unwind hint support madvenka 2023-02-02 7:40 ` madvenka 2023-02-02 7:40 ` [RFC PATCH v3 16/22] arm64: Add unwind hints to exception handlers madvenka 2023-02-02 7:40 ` madvenka 2023-02-02 7:40 ` [RFC PATCH v3 17/22] arm64: Add kernel and module support for ORC madvenka 2023-02-02 7:40 ` madvenka 2023-02-02 7:40 ` [RFC PATCH v3 18/22] arm64: Build the kernel with ORC information madvenka 2023-02-02 7:40 ` madvenka 2023-02-10 7:52 ` Tomohiro Misono (Fujitsu) 2023-02-10 7:52 ` Tomohiro Misono (Fujitsu) 2023-02-11 4:34 ` Madhavan T. Venkataraman 2023-02-11 4:34 ` Madhavan T. Venkataraman 2023-02-02 7:40 ` [RFC PATCH v3 19/22] arm64: unwinder: Add a reliability check in the unwinder based on ORC madvenka 2023-02-02 7:40 ` madvenka 2023-02-23 4:07 ` Suraj Jitindar Singh 2023-02-23 4:07 ` Suraj Jitindar Singh 2023-03-06 16:52 ` Madhavan T. Venkataraman 2023-03-06 16:52 ` Madhavan T. Venkataraman 2023-02-02 7:40 ` [RFC PATCH v3 20/22] arm64: Define HAVE_DYNAMIC_FTRACE_WITH_ARGS madvenka 2023-02-02 7:40 ` madvenka 2023-02-02 7:40 ` [RFC PATCH v3 21/22] arm64: Define TIF_PATCH_PENDING for livepatch madvenka 2023-02-02 7:40 ` madvenka 2023-02-02 7:40 ` [RFC PATCH v3 22/22] arm64: Enable livepatch for ARM64 madvenka 2023-02-02 7:40 ` madvenka 2023-03-01 3:12 ` [RFC PATCH v3 00/22] arm64: livepatch: Use ORC for dynamic frame pointer validation Tomohiro Misono (Fujitsu) 2023-03-01 3:12 ` Tomohiro Misono (Fujitsu) 2023-03-02 16:23 ` Petr Mladek 2023-03-02 16:23 ` Petr Mladek 2023-03-03 9:40 ` Tomohiro Misono (Fujitsu) 2023-03-03 9:40 ` Tomohiro Misono (Fujitsu) 2023-03-06 16:58 ` Madhavan T. Venkataraman 2023-03-06 16:58 ` Madhavan T. Venkataraman 2023-03-06 16:57 ` Madhavan T. Venkataraman 2023-03-06 16:57 ` Madhavan T. Venkataraman 2023-03-23 17:17 ` Mark Rutland 2023-03-23 17:17 ` Mark Rutland 2023-04-08 3:40 ` Madhavan T. Venkataraman 2023-04-08 3:40 ` Madhavan T. Venkataraman 2023-04-11 13:25 ` Mark Rutland 2023-04-11 13:25 ` Mark Rutland 2023-04-12 4:17 ` Josh Poimboeuf 2023-04-12 4:17 ` Josh Poimboeuf 2023-04-12 4:48 ` Madhavan T. Venkataraman 2023-04-12 4:48 ` Madhavan T. Venkataraman 2023-04-12 4:50 ` Madhavan T. Venkataraman 2023-04-12 4:50 ` Madhavan T. Venkataraman 2023-04-12 5:01 ` Josh Poimboeuf 2023-04-12 5:01 ` Josh Poimboeuf 2023-04-12 14:50 ` Madhavan T. Venkataraman 2023-04-12 14:50 ` Madhavan T. Venkataraman 2023-04-12 15:52 ` Josh Poimboeuf 2023-04-12 15:52 ` Josh Poimboeuf 2023-04-13 14:59 ` Madhavan T. Venkataraman 2023-04-13 14:59 ` Madhavan T. Venkataraman 2023-04-13 16:30 ` Josh Poimboeuf 2023-04-13 16:30 ` Josh Poimboeuf 2023-04-15 4:27 ` Madhavan T. Venkataraman 2023-04-15 4:27 ` Madhavan T. Venkataraman 2023-04-15 5:05 ` Josh Poimboeuf 2023-04-15 5:05 ` Josh Poimboeuf 2023-04-15 16:15 ` Madhavan T. Venkataraman 2023-04-15 16:15 ` Madhavan T. Venkataraman 2023-04-16 8:21 ` Indu Bhagat 2023-04-16 8:21 ` Indu Bhagat 2023-04-13 17:04 ` Nick Desaulniers [this message] 2023-04-13 17:04 ` Nick Desaulniers 2023-04-13 18:15 ` Jose E. Marchesi 2023-04-13 18:15 ` Jose E. Marchesi 2023-04-15 4:14 ` Madhavan T. Venkataraman 2023-04-15 4:14 ` Madhavan T. Venkataraman 2023-12-14 20:49 ` ARM64 Livepatch based on SFrame Madhavan T. Venkataraman 2023-12-14 20:49 ` Madhavan T. Venkataraman 2023-12-15 13:04 ` Mark Rutland 2023-12-15 13:04 ` Mark Rutland 2023-12-15 15:15 ` Madhavan T. Venkataraman 2023-12-15 15:15 ` Madhavan T. Venkataraman 2023-04-03 22:26 [RFC PATCH v3 00/22] arm64: livepatch: Use ORC for dynamic frame pointer validation Dylan Hatch 2023-04-08 3:41 ` Madhavan T. Venkataraman 2023-04-08 3:41 ` Madhavan T. Venkataraman
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