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Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.97.1 #2 (Red Hat Linux)) id 1rwdcJ-0000000HZIl-1TGs; Tue, 16 Apr 2024 07:52:35 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 0630E30040C; Tue, 16 Apr 2024 09:52:35 +0200 (CEST) Date: Tue, 16 Apr 2024 09:52:34 +0200 From: Peter Zijlstra To: Mike Rapoport Cc: linux-kernel@vger.kernel.org, Andrew Morton , Andy Lutomirski , Arnd Bergmann , Catalin Marinas , Christoph Hellwig , Helge Deller , Lorenzo Stoakes , Luis Chamberlain , Mark Rutland , Masami Hiramatsu , Mathieu Desnoyers , Michael Ellerman , Palmer Dabbelt , Russell King , Song Liu , Steven Rostedt , Thomas Gleixner , Uladzislau Rezki , Will Deacon , bpf@vger.kernel.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-modules@vger.kernel.org, linux-parisc@vger.kernel.org, linux-riscv@lists.infradead.org, linux-trace-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, x86@kernel.org Subject: Re: [RFC PATCH 6/7] execmem: add support for cache of large ROX pages Message-ID: <20240416075234.GA31647@noisy.programming.kicks-ass.net> References: <20240411160526.2093408-1-rppt@kernel.org> <20240411160526.2093408-7-rppt@kernel.org> <20240415104750.GJ40213@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Apr 15, 2024 at 08:00:26PM +0300, Mike Rapoport wrote: > On Mon, Apr 15, 2024 at 12:47:50PM +0200, Peter Zijlstra wrote: > > On Thu, Apr 11, 2024 at 07:05:25PM +0300, Mike Rapoport wrote: > > > > > To populate the cache, a writable large page is allocated from vmalloc with > > > VM_ALLOW_HUGE_VMAP, filled with invalid instructions and then remapped as > > > ROX. > > > > > +static void execmem_invalidate(void *ptr, size_t size, bool writable) > > > +{ > > > + if (execmem_info->invalidate) > > > + execmem_info->invalidate(ptr, size, writable); > > > + else > > > + memset(ptr, 0, size); > > > +} > > > > +static void execmem_invalidate(void *ptr, size_t size, bool writeable) > > +{ > > + /* fill memory with INT3 instructions */ > > + if (writeable) > > + memset(ptr, 0xcc, size); > > + else > > + text_poke_set(ptr, 0xcc, size); > > +} > > > > Thing is, 0xcc (aka INT3_INSN_OPCODE) is not an invalid instruction. > > It raises #BP not #UD. > > Do you mean that _invalidate is a poor name choice or that it's necessary > to use an instruction that raises #UD? Poor naming, mostly. #BP handler will still scream bloody murder if the site is otherwise unclaimed. It just isn't an invalid instruction.