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Fri, 20 Aug 2021 19:31:06 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1629480666; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:in-reply-to:in-reply-to: references:references; bh=lRij2bTpSGXVMDbhycmb3su8DPnygSPG8qvXt1BdmMQ=; b=GaEhMARj8xGVHTj7bt43VnhjzJAALO983uuEfnVXcY7iemcXn6D2JzdeM5GpM5554eoedj 83L3SI19//s9Uf/driz3PyNsPgczirOiDKay/8/uEylpeovTWgsGglPxWYZn6L4uDnHyKB 4vZ6J6dPquVkf5++AYKhlLsuBQkTbeg= Date: Fri, 20 Aug 2021 19:31:43 +0200 From: Borislav Petkov To: Tony Luck Cc: Jue Wang , Ding Hui , naoya.horiguchi@nec.com, osalvador@suse.de, Youquan Song , huangcun@sangfor.com.cn, x86@kernel.org, linux-edac@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/3] x86/mce: Avoid infinite loop for copy from user recovery Message-ID: References: <20210706190620.1290391-1-tony.luck@intel.com> <20210818002942.1607544-1-tony.luck@intel.com> <20210818002942.1607544-2-tony.luck@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20210818002942.1607544-2-tony.luck@intel.com> Authentication-Results: imf27.hostedemail.com; dkim=pass header.d=alien8.de header.s=dkim header.b=GaEhMARj; dmarc=pass (policy=none) header.from=alien8.de; spf=pass (imf27.hostedemail.com: domain of bp@alien8.de designates 5.9.137.197 as permitted sender) smtp.mailfrom=bp@alien8.de X-Stat-Signature: 9hojszwjfew6e88q8swag335xoepo8jk X-Rspamd-Queue-Id: AEE3770000A4 X-Rspamd-Server: rspam05 X-HE-Tag: 1629480672-44861 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000010, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Aug 17, 2021 at 05:29:40PM -0700, Tony Luck wrote: > @@ -1287,17 +1291,34 @@ static void kill_me_maybe(struct callback_head *cb) > } > } > > -static void queue_task_work(struct mce *m, int kill_current_task) > +static void queue_task_work(struct mce *m, char *msg, int kill_current_task) > { > - current->mce_addr = m->addr; > - current->mce_kflags = m->kflags; > - current->mce_ripv = !!(m->mcgstatus & MCG_STATUS_RIPV); > - current->mce_whole_page = whole_page(m); > + int count = ++current->mce_count; > > - if (kill_current_task) > - current->mce_kill_me.func = kill_me_now; > - else > - current->mce_kill_me.func = kill_me_maybe; > + /* First call, save all the details */ > + if (count == 1) { > + current->mce_addr = m->addr; > + current->mce_kflags = m->kflags; > + current->mce_ripv = !!(m->mcgstatus & MCG_STATUS_RIPV); > + current->mce_whole_page = whole_page(m); > + > + if (kill_current_task) > + current->mce_kill_me.func = kill_me_now; > + else > + current->mce_kill_me.func = kill_me_maybe; > + } > + > + /* Ten is likley overkill. Don't expect more than two faults before task_work() */ "likely" > + if (count > 10) > + mce_panic("Too many machine checks while accessing user data", m, msg); Ok, aren't we too nasty here? Why should we panic the whole box even with 10 MCEs? It is still user memory... IOW, why not: if (count > 10) current->mce_kill_me.func = kill_me_now; and when we return, that user process dies immediately. > + /* Second or later call, make sure page address matches the one from first call */ > + if (count > 1 && (current->mce_addr >> PAGE_SHIFT) != (m->addr >> PAGE_SHIFT)) > + mce_panic("Machine checks to different user pages", m, msg); Same question here. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette