kkinen <jar...@profian.com>, Sami Tolvanen <samitolva...@google.com>, "Naveen N. Rao" <naveen.n....@linux.ibm.com>, Marco Elver <el...@google.com>, Kees Cook <keesc...@chromium.org>, Steven Rostedt <rost...@goodmis.org>, Nathan Chancellor <nat...@kernel.org>, "Russell King \(Oracle\)" <rmk+ker...@armlinux.org.uk>, Mark Brown <broo...@kernel.org>, Borislav Petkov <b...@alien8.de>, Alexander Egorenkov <egore...@linux.ibm.com>, Thomas Bogendoerfer <tsbog...@alpha.franken.de>, linux-par...@vger.kernel.org, Nathaniel McCallum <nathan...@profian.com>, Dmitry Torokhov <dmitry.torok...@gmail.com>, "David S. Miller" <da...@davemloft.net>, "Kirill A. Shutemov" <kirill.shute...@linux.intel.com>, Tobias Huschle <husc...@linux.ibm.com>, "Peter Zijlstra \(Intel\)" <pet...@infradead.org>, "H. Peter Anvin" <h...@zytor.com>, sparcli...@vger.kernel.org, Tiezhu Yang <yangtie...@loongson.cn>, Miroslav Benes <mbe...@suse.cz>, Chen Zhongjin <chenzhong...@huawei.com>, Ard Biesheuvel <a...@kernel.org>, X86 ML <x...@kernel.org>, Russell King <li...@armlinux.org.uk>, linux-ri...@lists.infradead.org, Ingo Molnar <mi...@redhat.com>, Aaron Tomlin <atom...@redhat.com>, Albert Ou <a...@eecs.berkeley.edu>, Heiko Carstens <h...@linux.ibm.com>, Liao Chang <liaocha...@huawei.com>, Paul Walmsley <paul.walms...@sifive.com>, Josh Poimboeuf <jpoim...@kernel.org>, Thomas Richter <tmri...@linux.ibm.com>, linux-m...@vger.kernel.org, Changbin Du <changbin...@intel.com>, Palmer Dabbelt <pal...@dabbelt.com>, linuxppc-dev@lists.ozlabs.org, linux-modu...@vger.kernel.org Errors-To: linuxppc-dev-bounces+archive=mail-archive....@lists.ozlabs.org Sender: "Linuxppc-dev" <linuxppc-dev-bounces+archive=mail-archive....@lists.ozlabs.org>
On Sun, Jun 12, 2022 at 09:30:41PM +0900, Masami Hiramatsu wrote: > On Wed, 8 Jun 2022 11:19:19 -0700 > Song Liu <s...@kernel.org> wrote: > > > On Wed, Jun 8, 2022 at 9:28 AM Ard Biesheuvel <a...@kernel.org> wrote: > > > > > > Hello Jarkko, > > > > > > On Wed, 8 Jun 2022 at 02:02, Jarkko Sakkinen <jar...@profian.com> wrote: > > > > > > > > Tracing with kprobes while running a monolithic kernel is currently > > > > impossible because CONFIG_KPROBES is dependent of CONFIG_MODULES. This > > > > dependency is a result of kprobes code using the module allocator for > > > > the > > > > trampoline code. > > > > > > > > Detaching kprobes from modules helps to squeeze down the user space, > > > > e.g. when developing new core kernel features, while still having all > > > > the nice tracing capabilities. > > > > > > > > For kernel/ and arch/*, move module_alloc() and module_memfree() to > > > > module_alloc.c, and compile as part of vmlinux when either > > > > CONFIG_MODULES > > > > or CONFIG_KPROBES is enabled. In addition, flag kernel module specific > > > > code with CONFIG_MODULES. > > > > > > > > As the result, kprobes can be used with a monolithic kernel. > > > > > > I think I may have mentioned this the previous time as well, but I > > > don't think this is the right approach. > > > > > > Kprobes uses alloc_insn_page() to allocate executable memory, but the > > > requirements for this memory are radically different compared to > > > loadable modules, which need to be within an arch-specific distance of > > > the core kernel, need KASAN backing etc etc. > > > > I think the distance of core kernel requirement is the same for kprobe > > alloc_insn_page and modules, no? > > This strongly depends on how kprobes (software breakpoint and > single-step) is implemented on the arch. For example, x86 implements > the so-called "kprobe-booster" which jumps back from the single > stepping trampoline buffer. Then the buffer address must be within > the range where it can jump to the original address. > However, if the arch implements single-step as an instruction > emulation, it has no such limitation. As far as I know, arm64 > will do emulation for the instructions which change PC register > and will do direct execution with another software breakpoint > for other instructions. > > Why I'm using module_alloc() for a generic function, is that > can cover the limitation most widely. > Thus, if we have CONFIG_ARCH_HAVE_ALLOC_INSN_PAGE flag and > kprobes can check it instead of using __weak function, the > kprobes may not need to depend on module_alloc() in general. OK, I guess this is what Luis meant. I'll try to carve up something based on this. BR, Jarkko
