Follow the steps of Linux Kernel Module Cheat #71
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Aug 25, 2021
…sprog21#18) Since the address of buffer is userspace address, it may trigger an unexpected fault on strlen(buffer). On Ubuntu 20.04.2 LTS ( 5.8.0-63-generic ), using strlen(buffer) will result in the following: [ 2168.010930] /proc/buffer1k created [ 2177.014347] BUG: unable to handle page fault for address: 00007fbbc2a17000 [ 2177.014355] #PF: supervisor read access in kernel mode [ 2177.014358] #PF: error_code(0x0000) - not-present page [ 2177.014361] PGD 80000003c61d0067 P4D 80000003c61d0067 PUD 3ee6c5067 PMD 40e1ff067 PTE 0 [ 2177.014369] Oops: 0000 [#1] SMP PTI [ 2177.014376] CPU: 7 PID: 4750 Comm: cat Tainted: P W OE 5.8.0-63-generic sysprog21#71~20.04.1-Ubuntu [ 2177.014387] RIP: 0010:procfile_read+0xb/0x20 [procfs2] [ 2177.014393] Code: Unable to access opcode bytes at RIP 0xffffffffc1253fe1. [ 2177.014396] RSP: 0018:ffffbc84412cbe78 EFLAGS: 00010286 [ 2177.014400] RAX: ffffffffc1254000 RBX: 0000000000020000 RCX: ffffbc84412cbef0 [ 2177.014403] RDX: 0000000000020000 RSI: 00007fbbc2a17000 RDI: ffffa057d2708f00 [ 2177.014406] RBP: ffffbc84412cbe80 R08: 0000000000000001 R09: 0000000000000000 [ 2177.014409] R10: 0000000000000000 R11: 0000000000000000 R12: ffffa0581de8ccc0 [ 2177.014411] R13: ffffa057d2708f00 R14: ffffbc84412cbef0 R15: 00007fbbc2a17000 [ 2177.014415] FS: 00007fbbc3bfa580(0000) GS:ffffa0582dbc0000(0000) knlGS:0000000000000000 [ 2177.014418] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 2177.014421] CR2: ffffffffc1253fe1 CR3: 00000003c611c004 CR4: 00000000003606e0 [ 2177.014424] Call Trace: [ 2177.014435] proc_reg_read+0x66/0x90 [ 2177.014441] vfs_read+0xaa/0x190 [ 2177.014446] ksys_read+0x67/0xe0 [ 2177.014451] __x64_sys_read+0x1a/0x20 [ 2177.014458] do_syscall_64+0x49/0xc0 [ 2177.014464] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ 2177.014467] RIP: 0033:0x7fbbc3b18142 [ 2177.014472] Code: c0 e9 c2 fe ff ff 50 48 8d 3d 3a ca 0a 00 e8 f5 19 02 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 [ 2177.014476] RSP: 002b:00007ffcf2d20d78 EFLAGS: 00000246 ORIG_RAX: 0000000000000000 [ 2177.014479] RAX: ffffffffffffffda RBX: 0000000000020000 RCX: 00007fbbc3b18142 [ 2177.014482] RDX: 0000000000020000 RSI: 00007fbbc2a17000 RDI: 0000000000000003 [ 2177.014485] RBP: 00007fbbc2a17000 R08: 00007fbbc2a16010 R09: 0000000000000000 [ 2177.014487] R10: 0000000000000022 R11: 0000000000000246 R12: 0000560f8ff081f0 [ 2177.014490] R13: 0000000000000003 R14: 0000000000020000 R15: 0000000000020000 [ 2177.014635] CR2: 00007fbbc2a17000 [ 2177.014639] ---[ end trace b71ff05c1b0a10f6 ]--- [ 2177.184174] RIP: 0010:procfile_read+0xb/0x20 [procfs2] [ 2177.184176] Code: Unable to access opcode bytes at RIP 0xffffffffc1253fe1. [ 2177.184177] RSP: 0018:ffffbc84412cbe78 EFLAGS: 00010286 [ 2177.184178] RAX: ffffffffc1254000 RBX: 0000000000020000 RCX: ffffbc84412cbef0 [ 2177.184179] RDX: 0000000000020000 RSI: 00007fbbc2a17000 RDI: ffffa057d2708f00 [ 2177.184180] RBP: ffffbc84412cbe80 R08: 0000000000000001 R09: 0000000000000000 [ 2177.184180] R10: 0000000000000000 R11: 0000000000000000 R12: ffffa0581de8ccc0 [ 2177.184181] R13: ffffa057d2708f00 R14: ffffbc84412cbef0 R15: 00007fbbc2a17000 [ 2177.184182] FS: 00007fbbc3bfa580(0000) GS:ffffa0582dbc0000(0000) knlGS:0000000000000000 [ 2177.184182] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 2177.184183] CR2: ffffffffc1253fe1 CR3: 00000003c611c004 CR4: 00000000003606e0
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Linux Kernel Module Cheat is an ideal environment for experimenting Linux kernel modules by means of system emulations such as QEMU. We should follow the steps for better developer experience (DX).
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