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([2a02:6b8:0:107:3e85:844d:5b1d:60a]) by smtp.gmail.com with ESMTPSA id u4-20020a05651c130400b0026e02eb613csm2053541lja.18.2022.11.14.06.43.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 14 Nov 2022 06:44:00 -0800 (PST) Message-ID: <3b7a841d-bbbd-6018-556f-d2414a5f02b2@gmail.com> Date: Mon, 14 Nov 2022 17:44:00 +0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.4.2 Subject: Re: [PATCH v2 5/5] x86/kasan: Populate shadow for shared chunk of the CPU entry area Content-Language: en-US To: Sean Christopherson , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org Cc: "H. Peter Anvin" , Alexander Potapenko , Andrey Konovalov , Dmitry Vyukov , Vincenzo Frascino , linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, syzbot+ffb4f000dc2872c93f62@syzkaller.appspotmail.com, syzbot+8cdd16fd5a6c0565e227@syzkaller.appspotmail.com References: <20221110203504.1985010-1-seanjc@google.com> <20221110203504.1985010-6-seanjc@google.com> From: Andrey Ryabinin In-Reply-To: <20221110203504.1985010-6-seanjc@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/10/22 23:35, Sean Christopherson wrote: > > + /* > + * Populate the shadow for the shared portion of the CPU entry area. > + * Shadows for the per-CPU areas are mapped on-demand, as each CPU's > + * area is randomly placed somewhere in the 512GiB range and mapping > + * the entire 512GiB range is prohibitively expensive. > + */ > + kasan_populate_early_shadow((void *)shadow_cea_begin, > + (void *)shadow_cea_per_cpu_begin); > + I know I suggested to use "early" here, but I just realized that this might be a problem. This will actually map shadow page for the 8 pages (KASAN_SHADOW_SCALE_SHIFT) of the original memory. In case there is some per-cpu entry area starting right at CPU_ENTRY_AREA_PER_CPU the shadow for it will be covered with kasan_early_shadow_page instead of the usual one. So we need to go back to your v1 PATCH, or alternatively we can round up CPU_ENTRY_AREA_PER_CPU #define CPU_ENTRY_AREA_PER_CPU (CPU_ENTRY_AREA_RO_IDT + PAGE_SIZE << KASAN_SHADOW_SCALE_SHIFT) Such change will also require fixing up max_cea calculation in init_cea_offsets() Going back kasan_populate_shadow() seems like safer and easier choice. The only disadvantage of it that we might waste 1 page, which is not much compared to the KASAN memory overhead. > kasan_populate_early_shadow((void *)shadow_cea_end, > kasan_mem_to_shadow((void *)__START_KERNEL_map)); >