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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3ABF2C4332F for ; Mon, 9 May 2022 16:52:37 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id C7D448D0001; Mon, 9 May 2022 12:52:36 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id C2C106B0074; Mon, 9 May 2022 12:52:36 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id ACEF48D0001; Mon, 9 May 2022 12:52:36 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 9F2B06B0073 for ; Mon, 9 May 2022 12:52:36 -0400 (EDT) Received: from smtpin22.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay13.hostedemail.com (Postfix) with ESMTP id 72EC560F94 for ; Mon, 9 May 2022 16:52:36 +0000 (UTC) X-FDA: 79446798312.22.F26EB53 Received: from mail-yb1-f181.google.com (mail-yb1-f181.google.com [209.85.219.181]) by imf22.hostedemail.com (Postfix) with ESMTP id 5F417C00A0 for ; Mon, 9 May 2022 16:52:34 +0000 (UTC) Received: by mail-yb1-f181.google.com with SMTP id j2so26122207ybu.0 for ; Mon, 09 May 2022 09:52:35 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=UXiFk325eT/uin6juY8MDs9uDbcZ0rRGYF4uwLrhYoM=; b=CU57t1DGavqfk6REfm4jRrmgtCHhA9Bxhq2YKjsvtcug8qNwcUw80SzW3L1amX/eub aWHrplchw1istxVlUaUqAhQHIEM8hsceFJO5JdyQz47ykHSStdl3M0N1JESaF9e0u5ET upwfQlac2YdqILyIu5hYCpNmJDkQ6jcNcvVSPUfOJR5QX3UaEFzcUOY5WJlp44FK8QKq kAJJMWIH9muaZmmyuxcPnCOPkOrgn8pItEUdQcV8XOUyXlezRsYugSSsA9pqfGIOaQcO 2+0WkYzqIPwPTT/I+Wky0adhyCLHO6M8xSl9FA8nkJWQ7OdR+VbR7QCM7s9ZqkuxB5N4 qpEQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=UXiFk325eT/uin6juY8MDs9uDbcZ0rRGYF4uwLrhYoM=; b=1qVi095m/KQqVTj3ts2vzpAJ98/TTt720gjVbwUj+7qIC9VQij9IGlI89yii7klX+Z RuSPeIYCID6aJFR9rFWvYFULbeGrZS4ke9rWJjAOjHgbwkxpzT/X1EqtMW8KniGyaveA xJ2E0zq4crA3fTUkstneR0kwBkE8luczwfKPYeBjvm9GTexKGBwG3dzStASCppcEUOGF cZbl9pfGW3DXjx81fLOXaakZqrstZHsWJ3kZSsajrbJaZVJAWbLRgsWrW1krbNTvfSsx htxQYTXUEr3pu3mTdCdkbuMZqarXshm5xiBZjoZQMDDsdh+M8kxC9zRh2cIehr1mWb3W 0gVw== X-Gm-Message-State: AOAM530tZqy2qWSsvyoErn8ST0fe8Xgh2xHpRcHhtjPN9JHvcjjvlgu0 64SOq+n6ykCfPx2rB1IfGJK1bl472pGAG7AQOS4Ncw== X-Google-Smtp-Source: ABdhPJzD5+vOjoR45J8vJybqt5bFVkZynODUV+GbSK3Xg47Qljq/cxhdIWBHvAQIVHV3k2CB3K52qDrkMO0vgvJva+4= X-Received: by 2002:a25:e7d1:0:b0:645:7216:d9d0 with SMTP id e200-20020a25e7d1000000b006457216d9d0mr14454488ybh.307.1652115155053; Mon, 09 May 2022 09:52:35 -0700 (PDT) MIME-Version: 1.0 References: <20220426164315.625149-1-glider@google.com> <20220426164315.625149-29-glider@google.com> <87a6c6y7mg.ffs@tglx> <87y1zjlhmj.ffs@tglx> <878rrfiqyr.ffs@tglx> <87k0ayhc43.ffs@tglx> <87h762h5c2.ffs@tglx> In-Reply-To: From: Alexander Potapenko Date: Mon, 9 May 2022 18:51:59 +0200 Message-ID: Subject: Re: [PATCH v3 28/46] kmsan: entry: handle register passing from uninstrumented code To: Thomas Gleixner Cc: Alexander Viro , Andrew Morton , Andrey Konovalov , Andy Lutomirski , Arnd Bergmann , Borislav Petkov , Christoph Hellwig , Christoph Lameter , David Rientjes , Dmitry Vyukov , Eric Dumazet , Greg Kroah-Hartman , Herbert Xu , Ilya Leoshkevich , Ingo Molnar , Jens Axboe , Joonsoo Kim , Kees Cook , Marco Elver , Mark Rutland , Matthew Wilcox , "Michael S. Tsirkin" , Pekka Enberg , Peter Zijlstra , Petr Mladek , Steven Rostedt , Vasily Gorbik , Vegard Nossum , Vlastimil Babka , kasan-dev , Linux Memory Management List , Linux-Arch , LKML Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 5F417C00A0 X-Stat-Signature: abdsndorziyj4ca73wugjsaex8jpiu1a X-Rspam-User: Authentication-Results: imf22.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=CU57t1DG; spf=pass (imf22.hostedemail.com: domain of glider@google.com designates 209.85.219.181 as permitted sender) smtp.mailfrom=glider@google.com; dmarc=pass (policy=reject) header.from=google.com X-HE-Tag: 1652115154-840739 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 Mon, May 9, 2022 at 6:50 PM Alexander Potapenko wrote: > > > The callchain is: > > > > asm_sysvec_apic_timer_interrupt <- ASM entry in gate > > sysvec_apic_timer_interrupt(regs) <- noinstr C entry point > > irqentry_enter(regs) <- unpoisons @reg > > __sysvec_apic_timer_interrupt(regs) <- the actual handler > > set_irq_regs(regs) <- stores regs > > local_apic_timer_interrupt() > > ... > > tick_handler() <- One of the 4 variants > > regs = get_irq_regs(); <- retrieves regs > > update_process_times(user_tick = user_mode(regs)) > > account_process_tick(user_tick) > > irqtime_account_process_tick(user_tick) > > line 382: } else if { user_tick } <- KMSAN complains > > > > I'm even more confused now. > > Ok, I think I know what's going on. > > Indeed, calling kmsan_unpoison_memory() in irqentry_enter() was > supposed to be enough, but we have code in kmsan_unpoison_memory() (as > well as other runtime functions) that checks for kmsan_in_runtime() > and bails out to prevent potential recursion if KMSAN code starts > calling itself. > > kmsan_in_runtime() is implemented as follows: > > ============================================== > static __always_inline bool kmsan_in_runtime(void) > { > if ((hardirq_count() >> HARDIRQ_SHIFT) > 1) > return true; > return kmsan_get_context()->kmsan_in_runtime; > } > ============================================== > (see the code here: > https://lore.kernel.org/lkml/20220426164315.625149-13-glider@google.com/#Z31mm:kmsan:kmsan.h) > > If we are running in the task context (in_task()==true), > kmsan_get_context() returns a per-task `struct *kmsan_ctx`. > If `in_task()==false` and `hardirq_count()>>HARDIRQ_SHIFT==1`, it > returns a per-CPU one. > Otherwise kmsan_in_runtime() is considered true to avoid dealing with > nested interrupts. > > So in the case when `hardirq_count()>>HARDIRQ_SHIFT` is greater than > 1, kmsan_in_runtime() becomes a no-op, which leads to false positives. Should be "kmsan_unpoison_memory() becomes a no-op..."