From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-it0-f69.google.com (mail-it0-f69.google.com [209.85.214.69]) by kanga.kvack.org (Postfix) with ESMTP id 819C48E0001 for ; Fri, 14 Sep 2018 01:11:32 -0400 (EDT) Received: by mail-it0-f69.google.com with SMTP id n194-v6so1165211itn.0 for ; Thu, 13 Sep 2018 22:11:32 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id h66-v6sor3732749ioa.276.2018.09.13.22.11.30 for (Google Transport Security); Thu, 13 Sep 2018 22:11:31 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: References: From: Dmitry Vyukov Date: Fri, 14 Sep 2018 07:11:09 +0200 Message-ID: Subject: Re: [PATCH v6 15/18] khwasan, arm64: add brk handler for inline instrumentation Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: To: Nick Desaulniers Cc: Jann Horn , Andrey Konovalov , Andrey Ryabinin , Alexander Potapenko , Catalin Marinas , Will Deacon , Christoph Lameter , Andrew Morton , Mark Rutland , Marc Zyngier , Dave Martin , Ard Biesheuvel , "Eric W . Biederman" , Ingo Molnar , Paul Lawrence , Geert Uytterhoeven , Arnd Bergmann , "Kirill A . Shutemov" , Greg KH , Kate Stewart , Mike Rapoport , kasan-dev , linux-doc@vger.kernel.org, LKML , Linux ARM , linux-sparse@vger.kernel.org, Linux Memory Management List , Linux Kbuild mailing list , Kostya Serebryany , Evgenii Stepanov , Lee Smith , Ramana Radhakrishnan , Jacob Bramley , Ruben Ayrapetyan , Mark Brand , Chintan Pandya , Vishwath Mohan On Thu, Sep 13, 2018 at 8:09 PM, 'Nick Desaulniers' via kasan-dev wrote: > On Thu, Sep 13, 2018 at 1:37 AM Dmitry Vyukov wrote: >> >> On Wed, Sep 12, 2018 at 7:39 PM, Jann Horn wrote: >> > On Wed, Sep 12, 2018 at 7:16 PM Dmitry Vyukov wrote: >> >> On Wed, Aug 29, 2018 at 1:35 PM, Andrey Konovalov wrote: >> > [...] >> >> > +static int khwasan_handler(struct pt_regs *regs, unsigned int esr) >> >> > +{ >> >> > + bool recover = esr & KHWASAN_ESR_RECOVER; >> >> > + bool write = esr & KHWASAN_ESR_WRITE; >> >> > + size_t size = KHWASAN_ESR_SIZE(esr); >> >> > + u64 addr = regs->regs[0]; >> >> > + u64 pc = regs->pc; >> >> > + >> >> > + if (user_mode(regs)) >> >> > + return DBG_HOOK_ERROR; >> >> > + >> >> > + kasan_report(addr, size, write, pc); >> >> > + >> >> > + /* >> >> > + * The instrumentation allows to control whether we can proceed after >> >> > + * a crash was detected. This is done by passing the -recover flag to >> >> > + * the compiler. Disabling recovery allows to generate more compact >> >> > + * code. >> >> > + * >> >> > + * Unfortunately disabling recovery doesn't work for the kernel right >> >> > + * now. KHWASAN reporting is disabled in some contexts (for example when >> >> > + * the allocator accesses slab object metadata; same is true for KASAN; >> >> > + * this is controlled by current->kasan_depth). All these accesses are >> >> > + * detected by the tool, even though the reports for them are not >> >> > + * printed. >> >> > + * >> >> > + * This is something that might be fixed at some point in the future. >> >> > + */ >> >> > + if (!recover) >> >> > + die("Oops - KHWASAN", regs, 0); >> >> >> >> Why die and not panic? Die seems to be much less used function, and it >> >> calls panic anyway, and we call panic in kasan_report if panic_on_warn >> >> is set. >> > >> > die() is vaguely equivalent to BUG(); die() and BUG() normally only >> > terminate the current process, which may or may not leave the system >> > somewhat usable, while panic() always brings down the whole system. >> > AFAIK panic() shouldn't be used unless you're in some very low-level >> > code where you know that trying to just kill the current process can't >> > work and the entire system is broken beyond repair. >> > >> > If KASAN traps on some random memory access, there's a good chance >> > that just killing the current process will allow at least parts of the >> > system to continue. I'm not sure whether BUG() or die() is more >> > appropriate here, but I think it definitely should not be a panic(). >> >> >> Nick, do you know if die() will be enough to catch problems on Android >> phones? panic_on_warn would turn this into panic, but I guess one does >> not want panic_on_warn on a canary phone. > > die() has arch specific implementations, so looking at: > > arch/arm64/kernel/traps.c:196#die > > it looks like panic is invoked if in_interrupt() or panic_on_oops(), > which is a configure option. So maybe the config for KHWASAN should > also enable that? Otherwise seems easy to forget. But maybe that > should remain configurable separately? > > Looking at the kernel configs for the Pixel 2, it does seem like > CONFIG_PANIC_ON_OOPS=y is already enabled. > https://android.googlesource.com/kernel/msm/+/android-msm-wahoo-4.4-pie/arch/arm64/configs/wahoo_defconfig#746 Then I think we are good here. > Specifically to catch problems on Android, our internal debug builds > can report on panics, but not oops, IIUC.