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[83.35.24.93]) by smtp.gmail.com with ESMTPSA id a9sm8817458wrv.37.2021.06.14.12.37.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 14 Jun 2021 12:37:55 -0700 (PDT) Subject: Re: [RFC PATCH v2 2/2] target/ppc: make gdb able to translate priviledged addresses To: "Bruno Larsen (billionai)" , qemu-devel@nongnu.org References: <20210614191630.101304-1-bruno.larsen@eldorado.org.br> <20210614191630.101304-2-bruno.larsen@eldorado.org.br> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Message-ID: Date: Mon, 14 Jun 2021 21:37:54 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: <20210614191630.101304-2-bruno.larsen@eldorado.org.br> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=philmd@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=philmd@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.2, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.489, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: farosas@linux.ibm.com, richard.henderson@linaro.org, luis.pires@eldorado.org.br, Greg Kurz , lucas.araujo@eldorado.org.br, fernando.valle@eldorado.org.br, qemu-ppc@nongnu.org, Miroslav Rezanina , matheus.ferst@eldorado.org.br, david@gibson.dropbear.id.au Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 6/14/21 9:16 PM, Bruno Larsen (billionai) wrote: > This patch changes ppc_cpu_get_phys_page_debug so that it is now > able to translate both, priviledged and real mode addresses > independently of whether the CPU executing it has those permissions > > This was mentioned by Fabiano as something that would be very useful to > help with debugging, but could possibly constitute a security issue if > that debug function can be called in some way by prodution code. the > solution was implemented such that it would be trivial to wrap it around > ifdefs for building only with --enable-debug, for instance, but we are > not sure this is the best approach, hence why it is an RFC. > > Suggested-by: Fabiano Rosas > Signed-off-by: Bruno Larsen (billionai) > --- > target/ppc/mmu_helper.c | 23 +++++++++++++++++++++++ > 1 file changed, 23 insertions(+) > > diff --git a/target/ppc/mmu_helper.c b/target/ppc/mmu_helper.c > index 9dcdf88597..41c727c690 100644 > --- a/target/ppc/mmu_helper.c > +++ b/target/ppc/mmu_helper.c > @@ -2947,6 +2947,29 @@ hwaddr ppc_cpu_get_phys_page_debug(CPUState *cs, vaddr addr) > cpu_mmu_index(&cpu->env, true), false)) { > return raddr & TARGET_PAGE_MASK; > } > + > + /* > + * This is a fallback, in case we're asking for priviledged memory to > + * be printed, but the PCU is not executing in a priviledged manner. > + * > + * The code could be considered a security vulnerability if > + * this function can be called in a scenario that does not involve > + * debugging. > + * Given the name and how useful using real addresses may be for > + * actually debugging, however, we decided to include it anyway and > + * discuss how to best avoid the possible security concerns. > + * The current plan is that, if there is a chance this code is called in > + * a production environment, we can surround it with ifdefs so that it > + * is only compiled with --enable-debug Nothing forbid us to use --enable-debug in a production environment. > + */ > + /* attempt to translate first with virtual addresses */ > + if (ppc_xlate(cpu, addr, MMU_DATA_LOAD, &raddr, &s, &p, 1, false) || > + ppc_xlate(cpu, addr, MMU_INST_FETCH, &raddr, &s, &p, 1, false) || > + /* if didn't work, attempt to translate with real addresses */ > + ppc_xlate(cpu, addr, MMU_DATA_LOAD, &raddr, &s, &p, 3, false) || > + ppc_xlate(cpu, addr, MMU_INST_FETCH, &raddr, &s, &p, 3, false)) { > + return raddr & TARGET_PAGE_MASK; > + } > return -1; > } > >