Yamada <masahi...@kernel.org>, Jarkko Sakkinen <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>, l inux-ri...@lists.infradead.org, X86 ML <x...@kernel.org>, Russell King <li...@armlinux.org.uk>, 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 Wed, Jun 08, 2022 at 06:27:51PM +0200, Ard Biesheuvel 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. OK, I apologize for my ignorance. It's been a while. > 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. > > This is why arm64, for instance, does not implement alloc_insn_page() > in terms of module_alloc() [and likely does not belong in this patch > for that reason] > > Is there any reason kprobes cannot simply use vmalloc()? All arch's, except nios2 use vmalloc() in the end for module_alloc(). nios2 uses kmalloc() for the reasons that I'm not aware of, but it does not support kprobes in the first place. Based on this, I think that could work out just fine. I could cope with that. BR, Jarkko
