From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 21AAFCA9EA0 for ; Mon, 4 Nov 2019 11:52:03 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id 7249521E6F for ; Mon, 4 Nov 2019 11:52:02 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7249521E6F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-17255-kernel-hardening=archiver.kernel.org@lists.openwall.com Received: (qmail 26329 invoked by uid 550); 4 Nov 2019 11:51:56 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Received: (qmail 26306 invoked from network); 4 Nov 2019 11:51:55 -0000 Date: Mon, 4 Nov 2019 11:51:39 +0000 From: Mark Rutland To: Sami Tolvanen Cc: Will Deacon , Catalin Marinas , Steven Rostedt , Masami Hiramatsu , Ard Biesheuvel , Dave Martin , Kees Cook , Laura Abbott , Marc Zyngier , Nick Desaulniers , Jann Horn , Miguel Ojeda , Masahiro Yamada , clang-built-linux@googlegroups.com, kernel-hardening@lists.openwall.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 03/17] arm64: kvm: stop treating register x18 as caller save Message-ID: <20191104115138.GB45140@lakrids.cambridge.arm.com> References: <20191018161033.261971-1-samitolvanen@google.com> <20191101221150.116536-1-samitolvanen@google.com> <20191101221150.116536-4-samitolvanen@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191101221150.116536-4-samitolvanen@google.com> User-Agent: Mutt/1.11.1+11 (2f07cb52) (2018-12-01) On Fri, Nov 01, 2019 at 03:11:36PM -0700, Sami Tolvanen wrote: > From: Ard Biesheuvel > > In preparation of reserving x18, stop treating it as caller save in > the KVM guest entry/exit code. Currently, the code assumes there is > no need to preserve it for the host, given that it would have been > assumed clobbered anyway by the function call to __guest_enter(). > Instead, preserve its value and restore it upon return. > > Link: https://patchwork.kernel.org/patch/9836891/ > Signed-off-by: Ard Biesheuvel > [Sami: updated commit message, switched from x18 to x29 for the guest context] > Signed-off-by: Sami Tolvanen > Reviewed-by: Kees Cook > --- > arch/arm64/kvm/hyp/entry.S | 41 +++++++++++++++++++------------------- > 1 file changed, 20 insertions(+), 21 deletions(-) > > diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S > index e5cc8d66bf53..c3c2d842c609 100644 > --- a/arch/arm64/kvm/hyp/entry.S > +++ b/arch/arm64/kvm/hyp/entry.S > @@ -23,6 +23,7 @@ > .pushsection .hyp.text, "ax" > Could we please add a note here, e.g. /* * We treat x18 as callee-saved as the host may use it as a platform * register (e.g. for shadow call stack). */ ... as that will avoid anyone trying to optimize this away in future after reading the AAPCS. > .macro save_callee_saved_regs ctxt > + str x18, [\ctxt, #CPU_XREG_OFFSET(18)] > stp x19, x20, [\ctxt, #CPU_XREG_OFFSET(19)] > stp x21, x22, [\ctxt, #CPU_XREG_OFFSET(21)] > stp x23, x24, [\ctxt, #CPU_XREG_OFFSET(23)] > @@ -32,6 +33,8 @@ > .endm > > .macro restore_callee_saved_regs ctxt > + // We assume \ctxt is not x18-x28 Probably worth s/assume/require/ here. Otherwise, this looks godo to me: Reviewed-by: Mark Rutland Mark. > + ldr x18, [\ctxt, #CPU_XREG_OFFSET(18)] > ldp x19, x20, [\ctxt, #CPU_XREG_OFFSET(19)] > ldp x21, x22, [\ctxt, #CPU_XREG_OFFSET(21)] > ldp x23, x24, [\ctxt, #CPU_XREG_OFFSET(23)] > @@ -48,7 +51,7 @@ ENTRY(__guest_enter) > // x0: vcpu > // x1: host context > // x2-x17: clobbered by macros > - // x18: guest context > + // x29: guest context > > // Store the host regs > save_callee_saved_regs x1 > @@ -67,31 +70,28 @@ alternative_else_nop_endif > ret > > 1: > - add x18, x0, #VCPU_CONTEXT > + add x29, x0, #VCPU_CONTEXT > > // Macro ptrauth_switch_to_guest format: > // ptrauth_switch_to_guest(guest cxt, tmp1, tmp2, tmp3) > // The below macro to restore guest keys is not implemented in C code > // as it may cause Pointer Authentication key signing mismatch errors > // when this feature is enabled for kernel code. > - ptrauth_switch_to_guest x18, x0, x1, x2 > + ptrauth_switch_to_guest x29, x0, x1, x2 > > // Restore guest regs x0-x17 > - ldp x0, x1, [x18, #CPU_XREG_OFFSET(0)] > - ldp x2, x3, [x18, #CPU_XREG_OFFSET(2)] > - ldp x4, x5, [x18, #CPU_XREG_OFFSET(4)] > - ldp x6, x7, [x18, #CPU_XREG_OFFSET(6)] > - ldp x8, x9, [x18, #CPU_XREG_OFFSET(8)] > - ldp x10, x11, [x18, #CPU_XREG_OFFSET(10)] > - ldp x12, x13, [x18, #CPU_XREG_OFFSET(12)] > - ldp x14, x15, [x18, #CPU_XREG_OFFSET(14)] > - ldp x16, x17, [x18, #CPU_XREG_OFFSET(16)] > - > - // Restore guest regs x19-x29, lr > - restore_callee_saved_regs x18 > - > - // Restore guest reg x18 > - ldr x18, [x18, #CPU_XREG_OFFSET(18)] > + ldp x0, x1, [x29, #CPU_XREG_OFFSET(0)] > + ldp x2, x3, [x29, #CPU_XREG_OFFSET(2)] > + ldp x4, x5, [x29, #CPU_XREG_OFFSET(4)] > + ldp x6, x7, [x29, #CPU_XREG_OFFSET(6)] > + ldp x8, x9, [x29, #CPU_XREG_OFFSET(8)] > + ldp x10, x11, [x29, #CPU_XREG_OFFSET(10)] > + ldp x12, x13, [x29, #CPU_XREG_OFFSET(12)] > + ldp x14, x15, [x29, #CPU_XREG_OFFSET(14)] > + ldp x16, x17, [x29, #CPU_XREG_OFFSET(16)] > + > + // Restore guest regs x18-x29, lr > + restore_callee_saved_regs x29 > > // Do not touch any register after this! > eret > @@ -114,7 +114,7 @@ ENTRY(__guest_exit) > // Retrieve the guest regs x0-x1 from the stack > ldp x2, x3, [sp], #16 // x0, x1 > > - // Store the guest regs x0-x1 and x4-x18 > + // Store the guest regs x0-x1 and x4-x17 > stp x2, x3, [x1, #CPU_XREG_OFFSET(0)] > stp x4, x5, [x1, #CPU_XREG_OFFSET(4)] > stp x6, x7, [x1, #CPU_XREG_OFFSET(6)] > @@ -123,9 +123,8 @@ ENTRY(__guest_exit) > stp x12, x13, [x1, #CPU_XREG_OFFSET(12)] > stp x14, x15, [x1, #CPU_XREG_OFFSET(14)] > stp x16, x17, [x1, #CPU_XREG_OFFSET(16)] > - str x18, [x1, #CPU_XREG_OFFSET(18)] > > - // Store the guest regs x19-x29, lr > + // Store the guest regs x18-x29, lr > save_callee_saved_regs x1 > > get_host_ctxt x2, x3 > -- > 2.24.0.rc1.363.gb1bccd3e3d-goog >