From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754651AbdBHOtm (ORCPT ); Wed, 8 Feb 2017 09:49:42 -0500 Received: from foss.arm.com ([217.140.101.70]:50122 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752061AbdBHOtk (ORCPT ); Wed, 8 Feb 2017 09:49:40 -0500 Date: Wed, 8 Feb 2017 14:10:58 +0000 From: Mark Rutland To: Peter Zijlstra Cc: Kees Cook , "Reshetova, Elena" , Greg KH , Arnd Bergmann , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Will Deacon , David Windsor , Hans Liljestrand , David Howells , LKML , "kernel-hardening@lists.openwall.com" Subject: Re: [kernel-hardening] Re: [PATCH 4/4] refcount: Report failures through CHECK_DATA_CORRUPTION Message-ID: <20170208141058.GG15459@leverpostej> References: <20170207083405.GV6500@twins.programming.kicks-ass.net> <20170207111011.GB28790@leverpostej> <20170207123630.GR6515@twins.programming.kicks-ass.net> <20170207135020.GA26173@leverpostej> <20170207150737.GM25813@worktop.programming.kicks-ass.net> <20170207160300.GB26173@leverpostej> <20170207173036.GS6515@twins.programming.kicks-ass.net> <20170207175542.GC26173@leverpostej> <20170208091250.GT6515@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170208091250.GT6515@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 08, 2017 at 10:12:50AM +0100, Peter Zijlstra wrote: > On x86 have have __ex_table and __bug_table. The former is used for all > sorts of things, including fixing up faults. > > Now, our struct exception_table_entry has a third field used to specify > a handler, see commit: > > 548acf19234d ("x86/mm: Expand the exception table logic to allow new handling options") Ah; neat! > Still, if we want to allow a generic implementation that does a function > call, the handler prototype should probably look like: > > void exception_value(unsigned long value); > > Which means the arch bits need a trampoline and we also need to encode > that. The best I've come up with is having nr_regs trampolines and > stuffing the trampoline function in the ->handler field and then using > the ->to field to encode the actual handler. > > Something like: > > #define EX_REG_HANDLER(_reg) \ > bool ex_handler_value_##_reg(const struct exception_table_entry *fixup, \ > struct pt_regs *regs, int trapnr) \ > { \ > void (*handler)(unsigned long) = \ > (void *)((unsigned long)&fixup->to + fixup->to); \ > \ > if (trapnr != X86_TRAP_UD) \ > return false; \ > \ > regs->ip += 2; /* size of UD2 instruction */ \ > handler(regs->_reg); \ > return true; \ > } > > EX_REG_HANDLER(bx); > EX_REG_HANDLER(cx); > ... > EX_REG_HANDLER(ss); > > > asm ( > " .macro reg_to_handler r\n" > " .irp rs,bx,cx,...,ss\n" > " .ifc \\r, %\\rs\n" > " ex_handler_value_\\rs\n" > " .endif\n" > " .endr\n" > " .endm\n" > ); > > #define EXCEPTION_VALUE(val, handler) \ > asm volatile ("1: ud2" \ > _ASM_EXTABLE_HANDLE(1b, handler, \ > reg_to_handler %0) \ > : : "r" (val)) > > > Where the generic version can simply be: > > #define EXCEPTION_VALUE(val, handler) handler((unsigned long)val) > > Makes sense? That all makes sense to me. I'll take a look at putting together an arm64 equivalent to the x86 extable patch, along with cleanup to our SW breakpoint code (which we use in lieu for x86's UD2). Thanks, Mark. From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 8 Feb 2017 14:10:58 +0000 From: Mark Rutland Message-ID: <20170208141058.GG15459@leverpostej> References: <20170207083405.GV6500@twins.programming.kicks-ass.net> <20170207111011.GB28790@leverpostej> <20170207123630.GR6515@twins.programming.kicks-ass.net> <20170207135020.GA26173@leverpostej> <20170207150737.GM25813@worktop.programming.kicks-ass.net> <20170207160300.GB26173@leverpostej> <20170207173036.GS6515@twins.programming.kicks-ass.net> <20170207175542.GC26173@leverpostej> <20170208091250.GT6515@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170208091250.GT6515@twins.programming.kicks-ass.net> Subject: Re: [kernel-hardening] Re: [PATCH 4/4] refcount: Report failures through CHECK_DATA_CORRUPTION To: Peter Zijlstra Cc: Kees Cook , "Reshetova, Elena" , Greg KH , Arnd Bergmann , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Will Deacon , David Windsor , Hans Liljestrand , David Howells , LKML , "kernel-hardening@lists.openwall.com" List-ID: On Wed, Feb 08, 2017 at 10:12:50AM +0100, Peter Zijlstra wrote: > On x86 have have __ex_table and __bug_table. The former is used for all > sorts of things, including fixing up faults. > > Now, our struct exception_table_entry has a third field used to specify > a handler, see commit: > > 548acf19234d ("x86/mm: Expand the exception table logic to allow new handling options") Ah; neat! > Still, if we want to allow a generic implementation that does a function > call, the handler prototype should probably look like: > > void exception_value(unsigned long value); > > Which means the arch bits need a trampoline and we also need to encode > that. The best I've come up with is having nr_regs trampolines and > stuffing the trampoline function in the ->handler field and then using > the ->to field to encode the actual handler. > > Something like: > > #define EX_REG_HANDLER(_reg) \ > bool ex_handler_value_##_reg(const struct exception_table_entry *fixup, \ > struct pt_regs *regs, int trapnr) \ > { \ > void (*handler)(unsigned long) = \ > (void *)((unsigned long)&fixup->to + fixup->to); \ > \ > if (trapnr != X86_TRAP_UD) \ > return false; \ > \ > regs->ip += 2; /* size of UD2 instruction */ \ > handler(regs->_reg); \ > return true; \ > } > > EX_REG_HANDLER(bx); > EX_REG_HANDLER(cx); > ... > EX_REG_HANDLER(ss); > > > asm ( > " .macro reg_to_handler r\n" > " .irp rs,bx,cx,...,ss\n" > " .ifc \\r, %\\rs\n" > " ex_handler_value_\\rs\n" > " .endif\n" > " .endr\n" > " .endm\n" > ); > > #define EXCEPTION_VALUE(val, handler) \ > asm volatile ("1: ud2" \ > _ASM_EXTABLE_HANDLE(1b, handler, \ > reg_to_handler %0) \ > : : "r" (val)) > > > Where the generic version can simply be: > > #define EXCEPTION_VALUE(val, handler) handler((unsigned long)val) > > Makes sense? That all makes sense to me. I'll take a look at putting together an arm64 equivalent to the x86 extable patch, along with cleanup to our SW breakpoint code (which we use in lieu for x86's UD2). Thanks, Mark.