On Sun, 2023-08-06 at 23:40 -0700, Yonghong Song wrote: > > On 8/6/23 4:23 PM, syzbot wrote: > > Hello, > > > > syzbot found the following issue on: > > > > HEAD commit: 25ad10658dc1 riscv, bpf: Adapt bpf trampoline to optimized.. > > git tree: bpf-next > > console+strace: https://syzkaller.appspot.com/x/log.txt?x=147cbb29a80000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=8acaeb93ad7c6aaa > > dashboard link: https://syzkaller.appspot.com/bug?extid=d61b595e9205573133b3 > > compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40 > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=14d73ccea80000 > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1276aedea80000 > > > > Downloadable assets: > > disk image: https://storage.googleapis.com/syzbot-assets/3d378cc13d42/disk-25ad1065.raw.xz > > vmlinux: https://storage.googleapis.com/syzbot-assets/44580fd5d1af/vmlinux-25ad1065.xz > > kernel image: https://storage.googleapis.com/syzbot-assets/840587618b41/bzImage-25ad1065.xz > > > > The issue was bisected to: > > > > commit 8100928c881482a73ed8bd499d602bab0fe55608 > > Author: Yonghong Song <yonghong.song@xxxxxxxxx> > > Date: Fri Jul 28 01:12:02 2023 +0000 > > > > bpf: Support new sign-extension mov insns > > Thanks for reporting. I will look into this ASAP. Hi Yonghong, I guess it's your night and my morning, so I did some initial assessment. The BPF program being loaded is: 0 : (62) *(u32 *)(r10 -8) = 553656332 1 : (bf) r1 = (s16)r10 2 : (07) r1 += -8 3 : (b7) r2 = 3 4 : (bd) if r2 <= r1 goto pc+0 5 : (85) call bpf_trace_printk#6 6 : (b7) r0 = 0 7 : (95) exit (Note: when using bpftool (prog dump xlated id <some-id>) the disassembly of the instruction #1 is incorrectly printed as "1: (bf) r1 = r10") The error occurs when instruction #5 (call to printk) is executed. An incorrect address for the format string is passed to printk. Disassembly of the jited program looks as follows: $ bpftool prog dump jited id <some-id> bpf_prog_ebeed182d92b487f: 0: nopl (%rax,%rax) 5: nop 7: pushq %rbp 8: movq %rsp, %rbp b: subq $8, %rsp 12: movl $553656332, -8(%rbp) 19: movswq %bp, %rdi ; <---- Note movswq %bp ! 1d: addq $-8, %rdi 21: movl $3, %esi 26: cmpq %rdi, %rsi 29: jbe 0x2b 2b: callq 0xffffffffe11c484c 30: xorl %eax, %eax 32: leave 33: retq Note jit instruction #19 corresponding to BPF instruction #1, which loads truncated and sign-extended value of %rbp's first byte as an address of format string. Here is how verifier log looks for (slightly modified) program: func#0 @0 0: R1=ctx(off=0,imm=0) R10=fp0 ; asm volatile (" \n\ 0: (b7) r1 = 553656332 ; R1_w=553656332 1: (63) *(u32 *)(r10 -8) = r1 ; R1_w=553656332 R10=fp0 fp-8=553656332 2: (bf) r1 = (s16)r10 ; R1_w=fp0 R10=fp0 3: (07) r1 += -8 ; R1_w=fp-8 4: (b7) r2 = 3 ; R2_w=3 5: (bd) if r2 <= r1 goto pc+0 ; R1_w=fp-8 R2_w=3 6: (85) call bpf_trace_printk#6 mark_precise: frame0: last_idx 6 first_idx 0 subseq_idx -1 ... mark_precise: frame0: falling back to forcing all scalars precise 7: R0=scalar() 7: (b7) r0 = 0 ; R0_w=0 8: (95) exit from 5 to 6: R1_w=fp-8 R2_w=3 R10=fp0 fp-8=553656332 6: (85) call bpf_trace_printk#6 mark_precise: frame0: last_idx 6 first_idx 0 subseq_idx -1 ... mark_precise: frame0: falling back to forcing all scalars precise 7: safe Note the following line: 2: (bf) r1 = (s16)r10 ; R1_w=fp0 R10=fp0 Verifier incorrectly marked r1 as fp0, hence not noticing the problem with address passed to printk. Thanks, Eduard. > > > > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=17970c5da80000 > > final oops: https://syzkaller.appspot.com/x/report.txt?x=14570c5da80000 > > console output: https://syzkaller.appspot.com/x/log.txt?x=10570c5da80000 > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > Reported-by: syzbot+d61b595e9205573133b3@xxxxxxxxxxxxxxxxxxxxxxxxx > > Fixes: 8100928c8814 ("bpf: Support new sign-extension mov insns") > > > > general protection fault, probably for non-canonical address 0xdffffc0000000f4f: 0000 [#1] PREEMPT SMP KASAN > > KASAN: probably user-memory-access in range [0x0000000000007a78-0x0000000000007a7f] > > CPU: 1 PID: 0 Comm: swapper/1 Not tainted 6.5.0-rc2-syzkaller-00619-g25ad10658dc1 #0 > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2023 > > RIP: 0010:strnchr+0x25/0x80 lib/string.c:403 > > Code: 00 00 00 00 90 f3 0f 1e fa 53 48 01 fe 48 bb 00 00 00 00 00 fc ff df 48 83 ec 18 eb 28 48 89 f8 48 89 f9 48 c1 e8 03 83 e1 07 <0f> b6 04 18 38 c8 7f 04 84 c0 75 25 0f b6 07 38 d0 74 15 48 83 c7 > > RSP: 0018:ffffc90000177848 EFLAGS: 00010046 > > RAX: 0000000000000f4f RBX: dffffc0000000000 RCX: 0000000000000000 > > RDX: 0000000000000000 RSI: 0000000000007a7b RDI: 0000000000007a78 > > RBP: 0000000000000001 R08: 0000000000000005 R09: 0000000000000000 > > R10: 0000000000000003 R11: 0000000000000000 R12: 0000000000007a78 > > R13: ffffc900001779b0 R14: 0000000000000000 R15: 0000000000000003 > > FS: 0000000000000000(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000 > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > CR2: 00005611db5094b8 CR3: 0000000028ef0000 CR4: 00000000003506e0 > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > > Call Trace: > > <TASK> > > bpf_bprintf_prepare+0x127/0x1490 kernel/bpf/helpers.c:823 > > ____bpf_trace_printk kernel/trace/bpf_trace.c:385 [inline] > > bpf_trace_printk+0xdb/0x180 kernel/trace/bpf_trace.c:375 > > bpf_prog_ebeed182d92b487f+0x38/0x3c > > bpf_dispatcher_nop_func include/linux/bpf.h:1180 [inline] > > __bpf_prog_run include/linux/filter.h:609 [inline] > > bpf_prog_run include/linux/filter.h:616 [inline] > > __bpf_trace_run kernel/trace/bpf_trace.c:2269 [inline] > > bpf_trace_run1+0x148/0x400 kernel/trace/bpf_trace.c:2307 > > __bpf_trace_rcu_utilization+0x8e/0xc0 include/trace/events/rcu.h:27 > > trace_rcu_utilization+0xcd/0x120 include/trace/events/rcu.h:27 > > rcu_note_context_switch+0x6c/0x1ac0 kernel/rcu/tree_plugin.h:318 > > __schedule+0x293/0x59f0 kernel/sched/core.c:6610 > > schedule_idle+0x5b/0x80 kernel/sched/core.c:6814 > > do_idle+0x288/0x3f0 kernel/sched/idle.c:310 > > cpu_startup_entry+0x18/0x20 kernel/sched/idle.c:379 > > start_secondary+0x200/0x290 arch/x86/kernel/smpboot.c:326 > > secondary_startup_64_no_verify+0x167/0x16b > > </TASK> > > Modules linked in: > > ---[ end trace 0000000000000000 ]--- > > RIP: 0010:strnchr+0x25/0x80 lib/string.c:403 > > Code: 00 00 00 00 90 f3 0f 1e fa 53 48 01 fe 48 bb 00 00 00 00 00 fc ff df 48 83 ec 18 eb 28 48 89 f8 48 89 f9 48 c1 e8 03 83 e1 07 <0f> b6 04 18 38 c8 7f 04 84 c0 75 25 0f b6 07 38 d0 74 15 48 83 c7 > > RSP: 0018:ffffc90000177848 EFLAGS: 00010046 > > > > RAX: 0000000000000f4f RBX: dffffc0000000000 RCX: 0000000000000000 > > RDX: 0000000000000000 RSI: 0000000000007a7b RDI: 0000000000007a78 > > RBP: 0000000000000001 R08: 0000000000000005 R09: 0000000000000000 > > R10: 0000000000000003 R11: 0000000000000000 R12: 0000000000007a78 > > R13: ffffc900001779b0 R14: 0000000000000000 R15: 0000000000000003 > > FS: 0000000000000000(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000 > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > CR2: 00005611db5094b8 CR3: 0000000028ef0000 CR4: 00000000003506e0 > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > > ---------------- > > Code disassembly (best guess): > > 0: 00 00 add %al,(%rax) > > 2: 00 00 add %al,(%rax) > > 4: 90 nop > > 5: f3 0f 1e fa endbr64 > > 9: 53 push %rbx > > a: 48 01 fe add %rdi,%rsi > > d: 48 bb 00 00 00 00 00 movabs $0xdffffc0000000000,%rbx > > 14: fc ff df > > 17: 48 83 ec 18 sub $0x18,%rsp > > 1b: eb 28 jmp 0x45 > > 1d: 48 89 f8 mov %rdi,%rax > > 20: 48 89 f9 mov %rdi,%rcx > > 23: 48 c1 e8 03 shr $0x3,%rax > > 27: 83 e1 07 and $0x7,%ecx > > * 2a: 0f b6 04 18 movzbl (%rax,%rbx,1),%eax <-- trapping instruction > > 2e: 38 c8 cmp %cl,%al > > 30: 7f 04 jg 0x36 > > 32: 84 c0 test %al,%al > > 34: 75 25 jne 0x5b > > 36: 0f b6 07 movzbl (%rdi),%eax > > 39: 38 d0 cmp %dl,%al > > 3b: 74 15 je 0x52 > > 3d: 48 rex.W > > 3e: 83 .byte 0x83 > > 3f: c7 .byte 0xc7 > > > > > [...]
