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[2a01:4f8:190:11c2::b:1457]) by mx.google.com with ESMTPS id o12si4066587wrm.393.2019.02.11.10.22.28 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 11 Feb 2019 10:22:28 -0800 (PST) Received-SPF: pass (google.com: domain of bp@alien8.de designates 2a01:4f8:190:11c2::b:1457 as permitted sender) client-ip=2a01:4f8:190:11c2::b:1457; Authentication-Results: mx.google.com; dkim=pass header.i=@alien8.de header.s=dkim header.b=S1eK1s2W; spf=pass (google.com: domain of bp@alien8.de designates 2a01:4f8:190:11c2::b:1457 as permitted sender) smtp.mailfrom=bp@alien8.de; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=alien8.de Received: from zn.tnic (p200300EC2BC7A10074DEFDFE3AD6CF32.dip0.t-ipconnect.de [IPv6:2003:ec:2bc7:a100:74de:fdfe:3ad6:cf32]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id D5B721EC01B6; Mon, 11 Feb 2019 19:22:27 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1549909348; 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=mBrHsqt4hUkstq7VFx24ziqfy/NU+TGvc1tFvnBJ8PA=; b=S1eK1s2WDNc/02K3VAa86oPXXo4XoDwFmtP0wbeZYty5vAp9mprYozKcOct+xRxW15U4++ c3/M3JS0QgDRn5peV2kEMuTIRbxVT2WR5+ldKaRyWQt5dV1T85uygPXDKqWdlXpoIgzsRL kYmIwrctHP4YCZkqztXDQC87SbD3/S8= Date: Mon, 11 Feb 2019 19:22:21 +0100 From: Borislav Petkov To: Rick Edgecombe Cc: Andy Lutomirski , Ingo Molnar , linux-kernel@vger.kernel.org, x86@kernel.org, hpa@zytor.com, Thomas Gleixner , Nadav Amit , Dave Hansen , Peter Zijlstra , linux_dti@icloud.com, linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, akpm@linux-foundation.org, kernel-hardening@lists.openwall.com, linux-mm@kvack.org, will.deacon@arm.com, ard.biesheuvel@linaro.org, kristen@linux.intel.com, deneen.t.dock@intel.com, Nadav Amit Subject: Re: [PATCH v2 09/20] x86/kprobes: instruction pages initialization enhancements Message-ID: <20190211182221.GM19618@zn.tnic> References: <20190129003422.9328-1-rick.p.edgecombe@intel.com> <20190129003422.9328-10-rick.p.edgecombe@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190129003422.9328-10-rick.p.edgecombe@intel.com> User-Agent: Mutt/1.10.1 (2018-07-13) 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: Only nitpicks: > Subject: Re: [PATCH v2 09/20] x86/kprobes: instruction pages initialization enhancements Subject needs a verb. On Mon, Jan 28, 2019 at 04:34:11PM -0800, Rick Edgecombe wrote: > From: Nadav Amit > > Make kprobes instruction pages read-only (and executable) after they are > set to prevent them from mistaken or malicious modifications. > > This is a preparatory patch for a following patch that makes module > allocated pages non-executable and sets the page as executable after > allocation. > > While at it, do some small cleanup of what appears to be unnecessary > masking. > > Acked-by: Masami Hiramatsu > Signed-off-by: Nadav Amit > Signed-off-by: Rick Edgecombe > --- > arch/x86/kernel/kprobes/core.c | 24 ++++++++++++++++++++---- > 1 file changed, 20 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c > index 4ba75afba527..fac692e36833 100644 > --- a/arch/x86/kernel/kprobes/core.c > +++ b/arch/x86/kernel/kprobes/core.c > @@ -431,8 +431,20 @@ void *alloc_insn_page(void) > void *page; > > page = module_alloc(PAGE_SIZE); > - if (page) > - set_memory_ro((unsigned long)page & PAGE_MASK, 1); > + if (page == NULL) > + return NULL; Null tests we generally do like this: if (! ... like in the rest of this file. > + > + /* > + * First make the page read-only, and then only then make it executable s/then only then/only then/ ditto below. > + * to prevent it from being W+X in between. > + */ > + set_memory_ro((unsigned long)page, 1); > + > + /* > + * TODO: Once additional kernel code protection mechanisms are set, ensure > + * that the page was not maliciously altered and it is still zeroed. > + */ > + set_memory_x((unsigned long)page, 1); > > return page; > } > @@ -440,8 +452,12 @@ void *alloc_insn_page(void) > /* Recover page to RW mode before releasing it */ > void free_insn_page(void *page) > { > - set_memory_nx((unsigned long)page & PAGE_MASK, 1); > - set_memory_rw((unsigned long)page & PAGE_MASK, 1); > + /* > + * First make the page non-executable, and then only then make it > + * writable to prevent it from being W+X in between. > + */ > + set_memory_nx((unsigned long)page, 1); > + set_memory_rw((unsigned long)page, 1); > module_memfree(page); > } > > -- -- Regards/Gruss, Boris. Good mailing practices for 400: avoid top-posting and trim the reply.