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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id pj7-20020a17090b4f4700b00212e60c7d9csm2986668pjb.41.2022.10.27.11.58.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 27 Oct 2022 11:58:36 -0700 (PDT) Date: Thu, 27 Oct 2022 11:58:35 -0700 From: Kees Cook To: Alexander Potapenko Cc: Peter Zijlstra , Marco Elver , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Dave Hansen , x86@kernel.org Subject: Re: [PATCH] x86/uaccess: instrument copy_from_user_nmi() Message-ID: <202210271155.33956B1@keescook> References: <20221025221755.3810809-1-glider@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1666897118; a=rsa-sha256; cv=none; b=OfvS2Hct+ZwX6xO4fRzKFDB/3zoLMizZK1mjE8WEtpskNtjAoqG8tS/9pVBm4Onwkn7sPA rEkoNWc1MKnBltcUNelRI/wuSRWGCrFNtAzBePAdPBRds7FqVUZRnaz+/vGkc+tLvRlAH3 XysGmPP7BwRBio0krXRixiftxeWMuxA= ARC-Authentication-Results: i=1; imf15.hostedemail.com; dkim=pass header.d=chromium.org header.s=google header.b=V2XxrzoX; dmarc=pass (policy=none) header.from=chromium.org; spf=pass (imf15.hostedemail.com: domain of keescook@chromium.org designates 209.85.214.177 as permitted sender) smtp.mailfrom=keescook@chromium.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1666897118; h=from:from:sender: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:dkim-signature; bh=v0rEzPQriwPo47Lm4i24LI1bHNyCZGAXuw3tIRiGOno=; b=jZfeVdupwco4K/ZG2Ca6RMs21+4wEl8RXn4pgtqp2jBC0dPXr3JzeGj8fN6Bv6jm7AIDXS 7PrSzQdmRVGy/piRnV8tCvvr7ZqT0iXtFTvbBbWe1SS6PS+4qsTizBfS5HNT1VoOXS74oF GcFfzj+W8M3vjBHuKh0jUjjdADps65A= X-Stat-Signature: cij66qss8n3rknf5rerf5ts56qxy1y4h X-Rspamd-Queue-Id: C68C7A0024 X-Rspam-User: Authentication-Results: imf15.hostedemail.com; dkim=pass header.d=chromium.org header.s=google header.b=V2XxrzoX; dmarc=pass (policy=none) header.from=chromium.org; spf=pass (imf15.hostedemail.com: domain of keescook@chromium.org designates 209.85.214.177 as permitted sender) smtp.mailfrom=keescook@chromium.org X-Rspamd-Server: rspam09 X-HE-Tag: 1666897118-247040 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000038, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Oct 27, 2022 at 11:26:50AM -0700, Alexander Potapenko wrote: > On Thu, Oct 27, 2022 at 1:05 AM Peter Zijlstra wrote: > > > > On Wed, Oct 26, 2022 at 11:38:53AM -0700, Alexander Potapenko wrote: > > > A bigger issue from the NMI perspective is probably > > > having __msan_poison_alloca() inserted in every non-noinstr kernel > > > function, because that hook may acquire the stackdepot lock. > > > > *urgghhh* that's broken, that must not be. There is a *TON* of NMI > > functions that are non-noinstr. > > __msan_poison_alloca() is guarded by kmsan_in_runtime(), which is > currently implemented as: > > static __always_inline bool kmsan_in_runtime(void) > { > if ((hardirq_count() >> HARDIRQ_SHIFT) > 1) > return true; > return kmsan_get_context()->kmsan_in_runtime; > } > > I think the easiest way to fix the NMI situation would be adding "if > in_nmi() return true"? It might help to look through these threads: https://lore.kernel.org/lkml/20220916135953.1320601-1-keescook@chromium.org/ https://lore.kernel.org/all/20220919201648.2250764-1-keescook@chromium.org/ I wandered around attempting to deal with in_nmi(), etc. And in the end just drop the attempt to cover it. It's worth noting that copy_from_user_nmi() exists on 1 architecture and has exactly 1 call-site... -- Kees Cook