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Shutemov" Cc: Andy Lutomirski , Sean Christopherson , Andrew Morton , Joerg Roedel , Ard Biesheuvel , Andi Kleen , Kuppuswamy Sathyanarayanan , David Rientjes , Vlastimil Babka , Tom Lendacky , Thomas Gleixner , Peter Zijlstra , Paolo Bonzini , Ingo Molnar , Varad Gautam , Dario Faggioli , Dave Hansen , Mike Rapoport , David Hildenbrand , marcelo.cerri@canonical.com, tim.gardner@canonical.com, khalid.elmously@canonical.com, philip.cox@canonical.com, x86@kernel.org, linux-mm@kvack.org, linux-coco@lists.linux.dev, linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCHv7 10/14] x86/mm: Avoid load_unaligned_zeropad() stepping into unaccepted memory Message-ID: References: <20220614120231.48165-1-kirill.shutemov@linux.intel.com> <20220614120231.48165-11-kirill.shutemov@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20220614120231.48165-11-kirill.shutemov@linux.intel.com> ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1658856339; a=rsa-sha256; cv=none; b=rJ43E8kCX+C9GCYaAoM9DTUdQgpyCBnsKO3Cfug2Lf+PiJ936Q6Yy6dl378qs003RDKz40 2u3R31obo0vZxcLRT8qjXozARgN20l1PWWTjCKXQw2UpQ8aoYr0MVW8gKO6ixuT8bGAxGf q+G5oB+cGQ4fDkbYP6xDp2Pbr+beoOA= ARC-Authentication-Results: i=1; imf11.hostedemail.com; dkim=temperror ("DNS error when getting key") header.d=alien8.de header.s=dkim header.b="ql/OkaR/"; spf=temperror (imf11.hostedemail.com: error in processing during lookup of bp@alien8.de: DNS error) smtp.mailfrom=bp@alien8.de; dmarc=temperror reason="SPF/DKIM temp error" header.from=alien8.de (policy=temperror) ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1658856339; 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:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=Zc808cWbuiJ1LaEmAlRr5AvsxdqrezqcJtLhbo5Uy7g=; b=k54tCOyC9bESBQc2AIszdWrs3mA94IOdKvgFT/rdP2Mnt7iu3GcwoNh6FY1g6oNKf5lMMr VdAXpoN71knKIeG54nr2ofk+fzEk5icSyHv0kTTHppoRa0o2xMl49P/ybnfs5Hduk8IOFI CUiA3sxrFzlyEDAKShsfJCRuISeF77c= X-Rspamd-Server: rspam02 Authentication-Results: imf11.hostedemail.com; dkim=temperror ("DNS error when getting key") header.d=alien8.de header.s=dkim header.b="ql/OkaR/"; spf=temperror (imf11.hostedemail.com: error in processing during lookup of bp@alien8.de: DNS error) smtp.mailfrom=bp@alien8.de; dmarc=temperror reason="SPF/DKIM temp error" header.from=alien8.de (policy=temperror) X-Stat-Signature: wbtf3y4kabk7igt1wosufbwpzxp95rnb X-Rspamd-Queue-Id: 40A98400BB X-Rspam-User: X-HE-Tag: 1658856336-227320 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 Tue, Jun 14, 2022 at 03:02:27PM +0300, Kirill A. Shutemov wrote: > diff --git a/arch/x86/mm/unaccepted_memory.c b/arch/x86/mm/unaccepted_memory.c > index 1df918b21469..bcd56fe82b9e 100644 > --- a/arch/x86/mm/unaccepted_memory.c > +++ b/arch/x86/mm/unaccepted_memory.c > @@ -23,6 +23,38 @@ void accept_memory(phys_addr_t start, phys_addr_t end) > bitmap = __va(boot_params.unaccepted_memory); > range_start = start / PMD_SIZE; > > + /* > + * load_unaligned_zeropad() can lead to unwanted loads across page > + * boundaries. The unwanted loads are typically harmless. But, they > + * might be made to totally unrelated or even unmapped memory. > + * load_unaligned_zeropad() relies on exception fixup (#PF, #GP and now > + * #VE) to recover from these unwanted loads. > + * > + * But, this approach does not work for unaccepted memory. For TDX, a > + * load from unaccepted memory will not lead to a recoverable exception > + * within the guest. The guest will exit to the VMM where the only > + * recourse is to terminate the guest. > + * > + * There are three parts to fix this issue and comprehensively avoid > + * access to unaccepted memory. Together these ensure that an extra > + * “guard” page is accepted in addition to the memory that needs to be > + * used: > + * > + * 1. Implicitly extend the range_contains_unaccepted_memory(start, end) > + * checks up to end+2M if ‘end’ is aligned on a 2M boundary. > + * > + * 2. Implicitly extend accept_memory(start, end) to end+2M if ‘end’ is > + * aligned on a 2M boundary. Why do we need those unicode quotes and backticks in there? verify_diff: Warning: Unicode char [“] (0x8220 in line: + * “guard” page is accepted in addition to the memory that needs to be verify_diff: Warning: Unicode char [‘] (0x8216 in line: + * checks up to end+2M if ‘end’ is aligned on a 2M boundary. verify_diff: Warning: Unicode char [‘] (0x8216 in line: + * 2. Implicitly extend accept_memory(start, end) to end+2M if ‘end’ is verify_diff: Warning: Unicode char [‘] (0x8216 in line: + * needs to be done to make ‘page’ usable. That work might include verify_diff: Warning: Unicode char [‘] (0x8216 in line: + * accepting pages in addition to ‘page’ itself. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette