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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id d23sm14463482pfq.210.2020.04.07.10.01.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 07 Apr 2020 10:01:05 -0700 (PDT) Date: Tue, 7 Apr 2020 10:01:04 -0700 From: Kees Cook To: Peter Zijlstra Cc: tglx@linutronix.de, linux-kernel@vger.kernel.org, hch@infradead.org, sean.j.christopherson@intel.com, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, x86@kernel.org, kenny@panix.com, jeyu@kernel.org, rasmus.villemoes@prevas.dk, pbonzini@redhat.com, fenghua.yu@intel.com, xiaoyao.li@intel.com, nadav.amit@gmail.com, thellstrom@vmware.com, tony.luck@intel.com, rostedt@goodmis.org, gregkh@linuxfoundation.org, jannh@google.com, David.Laight@aculab.com, dcovelli@vmware.com, mhiramat@kernel.org Subject: Re: [PATCH 4/4] x86,module: Detect CRn and DRn manipulation Message-ID: <202004070958.CB8A3DA71D@keescook> References: <20200407110236.930134290@infradead.org> <20200407111007.429362016@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200407111007.429362016@infradead.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 07, 2020 at 01:02:40PM +0200, Peter Zijlstra wrote: > Since we now have infrastructure to analyze module text, disallow > modules that write to CRn and DRn registers. > > Signed-off-by: Peter Zijlstra (Intel) > --- > arch/x86/kernel/module.c | 21 +++++++++++++++++++++ > 1 file changed, 21 insertions(+) > > --- a/arch/x86/kernel/module.c > +++ b/arch/x86/kernel/module.c > @@ -266,6 +266,22 @@ static bool insn_is_vmx(struct insn *ins > return false; > } > > +static bool insn_is_mov_CRn(struct insn *insn) > +{ > + if (insn->opcode.bytes[0] == 0x0f && insn->opcode.bytes[1] == 0x22) > + return true; I always cringe at numeric literals. Would it be overkill to add defines for these (and the others that have comments next to them in 3/4)? It makes stuff easier to grep, etc. (e.g. we have register names in arch/x86/include/asm/asm.h, do we need instruction names somewhere else? I assume objtool has a bunch of this too...) -Kees > + > + return false; > +} > + > +static bool insn_is_mov_DRn(struct insn *insn) > +{ > + if (insn->opcode.bytes[0] == 0x0f && insn->opcode.bytes[1] == 0x23) > + return true; > + > + return false; > +} > + > static int decode_module(struct module *mod, void *text, void *text_end, bool sld_safe) > { > bool allow_vmx = sld_safe || !split_lock_enabled(); > @@ -285,6 +301,11 @@ static int decode_module(struct module * > return -ENOEXEC; > } > > + if (insn_is_mov_CRn(&insn) || insn_is_mov_DRn(&insn)) { > + pr_err("Module writes to CRn or DRn, please use the proper accessors: %s\n", mod->name); > + return -ENOEXEC; > + } > + > text += insn.length; > } > > > -- Kees Cook