Date: Thu, 17 Jan 2019 18:07:03 +0000 From: Nadav Amit <namit@...are.com> To: Masami Hiramatsu <mhiramat@...nel.org> CC: Rick Edgecombe <rick.p.edgecombe@...el.com>, Andy Lutomirski <luto@...nel.org>, Ingo Molnar <mingo@...hat.com>, Linux List Kernel Mailing <linux-kernel@...r.kernel.org>, the arch/x86 maintainers <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>, Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, Peter Zijlstra <peterz@...radead.org>, Damian Tometzki <linux_dti@...oud.com>, linux-integrity <linux-integrity@...r.kernel.org>, LSM List <linux-security-module@...r.kernel.org>, Andrew Morton <akpm@...ux-foundation.org>, Kernel Hardening <kernel-hardening@...ts.openwall.com>, Linux-MM <linux-mm@...ck.org>, Will Deacon <will.deacon@....com>, Ard Biesheuvel <ard.biesheuvel@...aro.org>, "kristen@...ux.intel.com" <kristen@...ux.intel.com>, "deneen.t.dock@...el.com" <deneen.t.dock@...el.com> Subject: Re: [PATCH 17/17] module: Prevent module removal racing with text_poke() > On Jan 16, 2019, at 11:54 PM, Masami Hiramatsu <mhiramat@...nel.org> wrote: > > On Wed, 16 Jan 2019 16:32:59 -0800 > Rick Edgecombe <rick.p.edgecombe@...el.com> wrote: > >> From: Nadav Amit <namit@...are.com> >> >> It seems dangerous to allow code modifications to take place >> concurrently with module unloading. So take the text_mutex while the >> memory of the module is freed. > > At that point, since the module itself is removed from module list, > it seems no actual harm. Or would you have any concern? So it appears that you are right and all the users of text_poke() and text_poke_bp() do install module notifiers, and remove the module from their internal data structure when they are done (*). As long as they prevent text_poke*() to be called concurrently (e.g., using jump_label_lock()), everything is fine. Having said that, the question is whether you “trust” text_poke*() users to do so. text_poke() description does not day explicitly that you need to prevent modules from being removed. What do you say? (*) I am not sure about kgdb, but it probably does not matter much
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