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[91.12.100.23]) by smtp.gmail.com with ESMTPSA id r1sm525475wrt.24.2021.08.18.11.02.30 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 18 Aug 2021 11:02:30 -0700 (PDT) Subject: Re: [PATCH] x86/mm: fix kern_addr_valid to cope with existing but not present entries To: Mike Rapoport Cc: x86@kernel.org, Andrew Morton , Andy Lutomirski , Dave Hansen , Ingo Molnar , Jiri Olsa , Mike Rapoport , Oscar Salvador , Peter Zijlstra , Thomas Gleixner , Borislav Petkov , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org References: <20210817135854.25407-1-rppt@kernel.org> From: David Hildenbrand Organization: Red Hat Message-ID: <218861a5-696f-6786-d1a1-bff5929360df@redhat.com> Date: Wed, 18 Aug 2021 20:02:29 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 18.08.21 19:42, Mike Rapoport wrote: > On Tue, Aug 17, 2021 at 04:01:13PM +0200, David Hildenbrand wrote: >> On 17.08.21 15:58, Mike Rapoport wrote: >>> From: Mike Rapoport >>> >>> Jiri Olsa reported a fault when running: >>> >>> # cat /proc/kallsyms | grep ksys_read >>> ffffffff8136d580 T ksys_read >>> # objdump -d --start-address=0xffffffff8136d580 --stop-address=0xffffffff8136d590 /proc/kcore >>> >>> /proc/kcore: file format elf64-x86-64 >>> >>> Segmentation fault >>> >>> krava33 login: [ 68.330612] general protection fault, probably for non-canonical address 0xf887ffcbff000: 0000 [#1] SMP PTI >>> [ 68.333118] CPU: 12 PID: 1079 Comm: objdump Not tainted 5.14.0-rc5qemu+ #508 >>> [ 68.334922] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-4.fc34 04/01/2014 >>> [ 68.336945] RIP: 0010:kern_addr_valid+0x150/0x300 >>> [ 68.338082] Code: 1f 40 00 48 8b 0d e8 12 61 01 48 85 f6 0f 85 ca 00 00 00 48 81 e1 00 f0 ff ff 48 21 c1 48 b8 00 00 00 00 80 88 ff ff 48 01 ca <48> 8b 3c 02 48 f7 c7 9f ff ff ff 0f 84 d8 fe ff ff 48 89 f8 0f 1f >>> [ 68.342220] RSP: 0018:ffffc90000bcbc38 EFLAGS: 00010206 >>> [ 68.343428] RAX: ffff888000000000 RBX: 0000000000001000 RCX: 000ffffffcbff000 >>> [ 68.345029] RDX: 000ffffffcbff000 RSI: 0000000000000000 RDI: 800ffffffcbff062 >>> [ 68.346599] RBP: ffffc90000bcbea8 R08: 0000000000001000 R09: 0000000000000000 >>> [ 68.349000] R10: 0000000000000000 R11: 0000000000001000 R12: 00007fcc0fd80010 >>> [ 68.350804] R13: ffffffff83400000 R14: 0000000000400000 R15: ffffffff843d23e0 >>> [ 68.352609] FS: 00007fcc111fcc80(0000) GS:ffff888275e00000(0000) knlGS:0000000000000000 >>> [ 68.354638] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >>> [ 68.356104] CR2: 00007fcc0fd80000 CR3: 000000011226e004 CR4: 0000000000770ee0 >>> [ 68.357896] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 >>> [ 68.359694] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 >>> [ 68.361597] PKRU: 55555554 >>> [ 68.362460] Call Trace: >>> [ 68.363252] read_kcore+0x57f/0x920 >>> [ 68.364289] ? rcu_read_lock_sched_held+0x12/0x80 >>> [ 68.365630] ? rcu_read_lock_sched_held+0x12/0x80 >>> [ 68.366955] ? rcu_read_lock_sched_held+0x12/0x80 >>> [ 68.368277] ? trace_hardirqs_on+0x1b/0xd0 >>> [ 68.369462] ? rcu_read_lock_sched_held+0x12/0x80 >>> [ 68.370793] ? lock_acquire+0x195/0x2f0 >>> [ 68.371920] ? lock_acquire+0x195/0x2f0 >>> [ 68.373035] ? rcu_read_lock_sched_held+0x12/0x80 >>> [ 68.374364] ? lock_acquire+0x195/0x2f0 >>> [ 68.375498] ? rcu_read_lock_sched_held+0x12/0x80 >>> [ 68.376831] ? rcu_read_lock_sched_held+0x12/0x80 >>> [ 68.379883] ? rcu_read_lock_sched_held+0x12/0x80 >>> [ 68.381268] ? lock_release+0x22b/0x3e0 >>> [ 68.382458] ? _raw_spin_unlock+0x1f/0x30 >>> [ 68.383685] ? __handle_mm_fault+0xcfc/0x15f0 >>> [ 68.384994] ? rcu_read_lock_sched_held+0x12/0x80 >>> [ 68.386389] ? lock_acquire+0x195/0x2f0 >>> [ 68.387573] ? rcu_read_lock_sched_held+0x12/0x80 >>> [ 68.388969] ? lock_release+0x22b/0x3e0 >>> [ 68.390145] proc_reg_read+0x55/0xa0 >>> [ 68.391257] ? vfs_read+0x78/0x1b0 >>> [ 68.392336] vfs_read+0xa7/0x1b0 >>> [ 68.393328] ksys_read+0x68/0xe0 >>> [ 68.394308] do_syscall_64+0x3b/0x90 >>> [ 68.395391] entry_SYSCALL_64_after_hwframe+0x44/0xae >>> [ 68.396804] RIP: 0033:0x7fcc11cf92e2 >>> [ 68.397824] Code: c0 e9 b2 fe ff ff 50 48 8d 3d ea 2e 0a 00 e8 95 e9 01 00 0f 1f 44 00 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 0f 05 <48> 3d 00 f0 ff ff 77 56 c3 0f 1f 44 00 00 48 83 ec 28 48 89 54 24 >>> [ 68.402420] RSP: 002b:00007ffd6e0f8da8 EFLAGS: 00000246 ORIG_RAX: 0000000000000000 >>> [ 68.404357] RAX: ffffffffffffffda RBX: 0000565439305b20 RCX: 00007fcc11cf92e2 >>> [ 68.406061] RDX: 0000000000800000 RSI: 00007fcc0f980010 RDI: 0000000000000003 >>> [ 68.407747] RBP: 00007fcc11dcd300 R08: 0000000000000003 R09: 00007fcc0d980010 >>> [ 68.410937] R10: 0000000003826000 R11: 0000000000000246 R12: 00007fcc0f980010 >>> [ 68.412624] R13: 0000000000000d68 R14: 00007fcc11dcc700 R15: 0000000000800000 >>> [ 68.414322] Modules linked in: intel_rapl_msr intel_rapl_common nfit kvm_intel kvm irqbypass rapl iTCO_wdt iTCO_vendor_support i2c_i801 i2c_smbus lpc_ich drm drm_panel_orientation_quirks zram xfs crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel >>> [ 68.419591] ---[ end trace e2c30f827226966b ]--- >>> [ 68.420969] RIP: 0010:kern_addr_valid+0x150/0x300 >>> [ 68.422308] Code: 1f 40 00 48 8b 0d e8 12 61 01 48 85 f6 0f 85 ca 00 00 00 48 81 e1 00 f0 ff ff 48 21 c1 48 b8 00 00 00 00 80 88 ff ff 48 01 ca <48> 8b 3c 02 48 f7 c7 9f ff ff ff 0f 84 d8 fe ff ff 48 89 f8 0f 1f >>> [ 68.426826] RSP: 0018:ffffc90000bcbc38 EFLAGS: 00010206 >>> [ 68.428150] RAX: ffff888000000000 RBX: 0000000000001000 RCX: 000ffffffcbff000 >>> [ 68.429813] RDX: 000ffffffcbff000 RSI: 0000000000000000 RDI: 800ffffffcbff062 >>> [ 68.431465] RBP: ffffc90000bcbea8 R08: 0000000000001000 R09: 0000000000000000 >>> [ 68.433115] R10: 0000000000000000 R11: 0000000000001000 R12: 00007fcc0fd80010 >>> [ 68.434768] R13: ffffffff83400000 R14: 0000000000400000 R15: ffffffff843d23e0 >>> [ 68.436423] FS: 00007fcc111fcc80(0000) GS:ffff888275e00000(0000) knlGS:0000000000000000 >>> [ 68.438354] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >>> [ 68.442077] CR2: 00007fcc0fd80000 CR3: 000000011226e004 CR4: 0000000000770ee0 >>> [ 68.443727] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 >>> [ 68.445370] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 >>> [ 68.447010] PKRU: 55555554 >>> >>> The fault happens because kern_addr_valid() dereferences existent but not >>> present PMD in the high kernel mappings. >>> >>> Such PMDs are created when free_kernel_image_pages() frees regions larger >>> than 2Mb. In this case a part of the freed memory is mapped with PMDs and >>> the set_memory_np_noalias() -> ... -> __change_page_attr() sequence will >>> mark the PMD as not present rather than wipe it completely. >>> >>> Make kern_addr_valid() to check whether higher level page table entries are >>> present before trying to dereference them to fix this issue and to avoid >>> similar issues in the future. >> >> Why not fix the setting code? > > Because I'm not sure it won't backfire in some other place. > Fixing kern_addr_valid() looks safe and easy for backporting. Fair enough, however it's somewhat unexpected to find e.g., !pmd_none() && !pmd_entry() in the direct map -- where no such thing as swapping exists. Anyhow, the x86 maintainers are the right people to make a call, I'm happy as long as it's fixed. -- Thanks, David / dhildenb