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[31.46.247.178]) by smtp.gmail.com with ESMTPSA id a7-20020a170906468700b009b957d5237asm1199002ejr.80.2023.10.18.01.44.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Oct 2023 01:44:53 -0700 (PDT) Sender: Ingo Molnar Date: Wed, 18 Oct 2023 10:44:51 +0200 From: Ingo Molnar To: Rick Edgecombe Cc: x86@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, luto@kernel.org, peterz@infradead.org, kirill.shutemov@linux.intel.com, elena.reshetova@intel.com, isaku.yamahata@intel.com, seanjc@google.com, Michael Kelley , thomas.lendacky@amd.com, decui@microsoft.com, sathyanarayanan.kuppuswamy@linux.intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org Subject: Re: [PATCH 02/10] x86/mm/cpa: Reject incorrect encryption change requests Message-ID: References: <20231017202505.340906-1-rick.p.edgecombe@intel.com> <20231017202505.340906-3-rick.p.edgecombe@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231017202505.340906-3-rick.p.edgecombe@intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Rick Edgecombe wrote: > Kernel memory is "encrypted" by default. Some callers may "decrypt" it > in order to share it with things outside the kernel like a device or an > untrusted VMM. > > There is nothing to stop set_memory_encrypted() from being passed memory > that is already "encrypted" (aka. "private" on TDX). In fact, some > callers do this because ... $REASONS. Unfortunately, part of the TDX > decrypted=>encrypted transition is truly one way*. It can't handle > being asked to encrypt an already encrypted page > > Allow __set_memory_enc_pgtable() to detect already-encrypted memory > before it hits the TDX code. > > * The one way part is "page acceptance" > > [commit log written by Dave Hansen] > Signed-off-by: Rick Edgecombe > --- > arch/x86/mm/pat/set_memory.c | 41 +++++++++++++++++++++++++++++++++++- > 1 file changed, 40 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c > index bda9f129835e..1238b0db3e33 100644 > --- a/arch/x86/mm/pat/set_memory.c > +++ b/arch/x86/mm/pat/set_memory.c > @@ -2122,6 +2122,21 @@ int set_memory_global(unsigned long addr, int numpages) > __pgprot(_PAGE_GLOBAL), 0); > } > > +static bool kernel_vaddr_encryped(unsigned long addr, bool enc) > +{ > + unsigned int level; > + pte_t *pte; > + > + pte = lookup_address(addr, &level); > + if (!pte) > + return false; > + > + if (enc) > + return pte_val(*pte) == cc_mkenc(pte_val(*pte)); > + > + return pte_val(*pte) == cc_mkdec(pte_val(*pte)); > +} > + > /* > * __set_memory_enc_pgtable() is used for the hypervisors that get > * informed about "encryption" status via page tables. > @@ -2130,7 +2145,7 @@ static int __set_memory_enc_pgtable(unsigned long addr, int numpages, bool enc) > { > pgprot_t empty = __pgprot(0); > struct cpa_data cpa; > - int ret; > + int ret, numpages_in_state = 0; > > /* Should not be working on unaligned addresses */ > if (WARN_ONCE(addr & ~PAGE_MASK, "misaligned address: %#lx\n", addr)) > @@ -2143,6 +2158,30 @@ static int __set_memory_enc_pgtable(unsigned long addr, int numpages, bool enc) > cpa.mask_clr = enc ? pgprot_decrypted(empty) : pgprot_encrypted(empty); > cpa.pgd = init_mm.pgd; > > + /* > + * If any page is already in the right state, bail with an error > + * because the code doesn't handled it. This is likely because Grammar mistake here. > + * something has gone wrong and isn't worth optimizing for. > + * > + * If all the memory pages are already in the desired state return > + * success. Missing comma. > + * > + * kernel_vaddr_encryped() does not synchronize against huge page > + * splits so take pgd_lock. A caller doing strange things could Missing comma. Thanks, Ingo