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Wed, 5 May 2021 10:37:29 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 57BA52D6DCEF9; Wed, 5 May 2021 10:37:29 +0200 (CEST) Date: Wed, 5 May 2021 10:37:29 +0200 From: Peter Zijlstra To: Kees Cook Cc: Rick Edgecombe , dave.hansen@intel.com, luto@kernel.org, linux-mm@kvack.org, x86@kernel.org, akpm@linux-foundation.org, linux-hardening@vger.kernel.org, kernel-hardening@lists.openwall.com, ira.weiny@intel.com, rppt@kernel.org, dan.j.williams@intel.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH RFC 0/9] PKS write protected page tables Message-ID: References: <20210505003032.489164-1-rick.p.edgecombe@intel.com> <202105042253.ECBBF6B6@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <202105042253.ECBBF6B6@keescook> X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: AA0F4C0007C4 X-Stat-Signature: jrx7p3zdikh39jxntybbpf66od1bf4f7 Authentication-Results: imf06.hostedemail.com; dkim=pass header.d=infradead.org header.s=desiato.20200630 header.b=jkvUVKoh; spf=none (imf06.hostedemail.com: domain of peterz@infradead.org has no SPF policy when checking 90.155.92.199) smtp.mailfrom=peterz@infradead.org; dmarc=none Received-SPF: none (infradead.org>: No applicable sender policy available) receiver=imf06; identity=mailfrom; envelope-from=""; helo=desiato.infradead.org; client-ip=90.155.92.199 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1620203860-548786 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, May 04, 2021 at 11:25:31PM -0700, Kees Cook wrote: > It looks like PKS-protected page tables would be much like the > RO-protected text pages in the sense that there is already code in > the kernel to do things to make it writable, change text, and set it > read-only again (alternatives, ftrace, etc). We don't actually modify text by changing the mapping at all. We modify through a writable (but not executable) temporary alias on the page (on x86). Once a mapping is RX it will *never* be writable again (until we tear it all down).