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Message-ID: <CANypQFYQSxyaNEUeOKq4dvNe+jhcw3mna2ho0ZARth5cXj6YxA@mail.gmail.com> Date: Tue, 10 Feb 2026 21:07:13 +0800 From: Jiaming Zhang <r772577952@...il.com> To: linux-kernel@...r.kernel.org Cc: brauner@...nel.org, jack@...e.cz, linux-fsdevel@...r.kernel.org, viro@...iv.linux.org.uk, syzkaller@...glegroups.com Subject: [Linux Kernel Bug] WARNING in exc_debug_kernel Dear Linux kernel developers and maintainers, We are writing to report a WARNING discovered in the system with our generated syzkaller specifications. This issue is reproducible on the latest version of linux (v6.19, commit 05f7e89ab9731565d8a62e3b5d1ec206485eeb0b). We are trying to analyze the root cause. Currently, we found that the WARNING can be triggered when the following conditions are satisfied: !cpu_feature_enabled(X86_FEATURE_FRED)=true dr6=16385 (0x4001), i.e. dr6=(DT_STEP|DR_TRAP0) is_sysenter_singlestep(regs)=false Intuitively, the results of is_sysenter_singlestep(regs) and !!(dr6 & DR_STEP) should be consistent, but this is not the case. We suspect that some previously executed syscalls may have corrupted the consistency. We have attached the kernel console output, kernel config, and reproducers to assist with the analysis: .config file: https://drive.google.com/file/d/1Ybz9U1r0sJQ83PPzFcLn5vIaKBFyvehI/view?usp=drive_link kernel console output: https://drive.google.com/file/d/1cNWDnkNrSeGXLvi2E9a3FfJ-LsfFVl2b/view?usp=drive_link symbolized report: https://drive.google.com/file/d/1yHP847poR1PIPzc-0Xvt2x-PWWHz0CVC/view?usp=drive_link C reproducer: https://drive.google.com/file/d/13mJobL3WVKZL31ZzvY0o8WXa_HZZescr/view?usp=drive_link syz reproducer: https://drive.google.com/file/d/1UVuNeYMhOQuQD-p1u90xy3DopzPtBVJG/view?usp=drive_link The issue report is also listed below (symbolized by syz-symbolize): --- ------------[ cut here ]------------ WARNING: arch/x86/kernel/traps.c:1284 at exc_debug_kernel+0x108/0x150 vol/linux/v6.19/arch/x86/kernel/traps.c:1284, CPU#0: repro.out/9697 Modules linked in: CPU: 0 UID: 0 PID: 9697 Comm: repro.out Not tainted 6.19.0 #1 PREEMPT(full) Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014 RIP: 0010:exc_debug_kernel+0x108/0x150 vol/linux/v6.19/arch/x86/kernel/traps.c:1284 Code: ff 65 48 8b 05 d9 ef 1d 07 48 3b 44 24 08 75 26 48 83 c4 10 5b 41 5e 41 5f 5d e9 ae 60 da f5 cc 90 0f 0b 90 e9 71 ff ff ff 90 <0f> 0b 90 80 a3 91 00 00 00 fe eb b5 e8 87 3f 00 00 f3 0f 1e fa 41 RSP: 0018:fffffe0000016f20 EFLAGS: 00010002 RAX: ffffffff815bfe00 RBX: fffffe0000016f58 RCX: 0000000000110000 RDX: ffff8880219ebd80 RSI: 0000000000000000 RDI: 0000000000008001 RBP: 0000000000000001 R08: ffffffff8f5d9377 R09: 1ffffffff1ebb26e R10: dffffc0000000000 R11: ffffffff8169a7c0 R12: 0000000000000000 R13: 0000000000000000 R14: 0000000000004001 R15: 0000000000050202 FS: 0000000029677300(0000) GS:ffff8880994e3000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000000 CR3: 000000004c4c7000 CR4: 0000000000750ef0 DR0: 0000000000000006 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 PKRU: 55555554 Call Trace: <#DB> asm_exc_debug+0x1e/0x40 vol/linux/v6.19/arch/x86/include/asm/idtentry.h:654 RIP: 0010:copy_user_generic vol/linux/v6.19/arch/x86/include/asm/uaccess_64.h:126 [inline] RIP: 0010:raw_copy_to_user vol/linux/v6.19/arch/x86/include/asm/uaccess_64.h:147 [inline] RIP: 0010:_inline_copy_to_user vol/linux/v6.19/include/linux/uaccess.h:206 [inline] RIP: 0010:_copy_to_user+0x85/0xb0 vol/linux/v6.19/lib/usercopy.c:26 Code: e8 70 3f 3e fd 4d 39 fc 72 3d 4d 39 ec 77 38 e8 01 3d 3e fd 4c 89 f7 89 de e8 c7 15 a6 fd 0f 01 cb 4c 89 ff 48 89 d9 4c 89 f6 <f3> a4 0f 1f 00 48 89 cb 0f 01 ca 48 89 d8 5b 41 5c 41 5d 41 5e 41 RSP: 0018:ffffc9000bbbfdd0 EFLAGS: 00050256 RAX: ffffffff84788d01 RBX: 0000000000000008 RCX: 0000000000000001 RDX: 0000000000000000 RSI: ffffc9000bbbfe27 RDI: 0000000000000007 RBP: ffffc9000bbbfec0 R08: ffffc9000bbbfe27 R09: 1ffff92001777fc4 R10: dffffc0000000000 R11: fffff52001777fc5 R12: 0000000000000008 R13: 00007ffffffff000 R14: ffffc9000bbbfe20 R15: 0000000000000000 </#DB> <TASK> copy_to_user vol/linux/v6.19/include/linux/uaccess.h:236 [inline] do_pipe2+0xc2/0x170 vol/linux/v6.19/fs/pipe.c:1040 __do_sys_pipe2 vol/linux/v6.19/fs/pipe.c:1056 [inline] __se_sys_pipe2 vol/linux/v6.19/fs/pipe.c:1054 [inline] __x64_sys_pipe2+0x5a/0x70 vol/linux/v6.19/fs/pipe.c:1054 do_syscall_x64 vol/linux/v6.19/arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xe8/0xf80 vol/linux/v6.19/arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x44d989 Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 b1 14 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007ffe605f93e8 EFLAGS: 00000206 ORIG_RAX: 0000000000000125 RAX: ffffffffffffffda RBX: 0000000000400488 RCX: 000000000044d989 RDX: 000000000044d989 RSI: 0000000000000000 RDI: 0000000000000000 RBP: 00007ffe605f9400 R08: 0000000000000000 R09: 00007ffe605f9400 R10: ffffffffffffffff R11: 0000000000000206 R12: 000000000040bf20 R13: 0000000000000000 R14: 00000000004ba018 R15: 0000000000400488 </TASK> ---------------- Code disassembly (best guess): 0: e8 70 3f 3e fd call 0xfd3e3f75 5: 4d 39 fc cmp %r15,%r12 8: 72 3d jb 0x47 a: 4d 39 ec cmp %r13,%r12 d: 77 38 ja 0x47 f: e8 01 3d 3e fd call 0xfd3e3d15 14: 4c 89 f7 mov %r14,%rdi 17: 89 de mov %ebx,%esi 19: e8 c7 15 a6 fd call 0xfda615e5 1e: 0f 01 cb stac 21: 4c 89 ff mov %r15,%rdi 24: 48 89 d9 mov %rbx,%rcx 27: 4c 89 f6 mov %r14,%rsi * 2a: f3 a4 rep movsb %ds:(%rsi),%es:(%rdi) <-- trapping instruction 2c: 0f 1f 00 nopl (%rax) 2f: 48 89 cb mov %rcx,%rbx 32: 0f 01 ca clac 35: 48 89 d8 mov %rbx,%rax 38: 5b pop %rbx 39: 41 5c pop %r12 3b: 41 5d pop %r13 3d: 41 5e pop %r14 3f: 41 rex.B --- Please let me know if any further information is required. Best Regards, Jiaming Zhang
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