[syzbot] [kernel?] BUG: unable to handle kernel paging request in write_comp_data

[syzbot] [kernel?] BUG: unable to handle kernel paging request in write_comp_data

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    a2cf4ef33184 Merge tag 'devicetree-fixes-for-7.2' of git:/..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16c0cc9e580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f221a1b5d497ed15
dashboard link: https://syzkaller.appspot.com/bug?extid=237f670105a254a230d4
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/6eb03d1a0722/disk-a2cf4ef3.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/4e0d90b14d28/vmlinux-a2cf4ef3.xz
kernel image: https://storage.googleapis.com/syzbot-assets/9b81b6ecaa65/bzImage-a2cf4ef3.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+237f670105a254a230d4@syzkaller.appspotmail.com

BUG: unable to handle page fault for address: ffffc90013ccbfe8
#PF: supervisor write access in kernel mode
#PF: error_code(0x0002) - not-present page
PGD 13fe60067 P4D 13fe60067 PUD 1cafa067 PMD 61350067 PTE 0
Oops: Oops: 0002 [#1] SMP KASAN PTI
CPU: 0 UID: 0 PID: 19114 Comm: syz.3.1830 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:write_comp_data+0x75/0x90 kernel/kcov.c:267
Code: 00 8b bf fc 16 00 00 48 8b 30 48 c1 e7 03 4c 8d 1c b5 00 00 00 00 4a 8d 14 dd 28 00 00 00 48 39 d7 72 bd 48 83 c6 01 48 89 30 <4c> 89 44 10 e0 4c 89 4c 10 e8 4c 89 54 10 f0 4a 89 4c d8 20 c3 cc
RSP: 0018:ffffc90005a57e78 EFLAGS: 00050257
RAX: ffffc90013ccc000 RBX: 0000000000000000 RCX: ffffffff824589a5
RDX: 0000000000000008 RSI: 0000000000000000 RDI: 0000000000400000
RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000002
R10: 0000000000000001 R11: fffffffffffffffc R12: 0000000000000020
R13: 0000000000000000 R14: 00007ffffffff000 R15: 0000000000000001
FS:  00007fa950b4b6c0(0000) GS:ffff888123de1000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffc90013ccbfe8 CR3: 000000005848c000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 rseq_register+0x115/0x350 kernel/rseq.c:460
 __do_sys_rseq kernel/rseq.c:561 [inline]
 __se_sys_rseq kernel/rseq.c:547 [inline]
 __x64_sys_rseq+0x1b8/0x2e0 kernel/rseq.c:547
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x115/0x840 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fa95359e019
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fa950b4b028 EFLAGS: 00000246 ORIG_RAX: 000000000000014e
RAX: ffffffffffffffda RBX: 00007fa953826450 RCX: 00007fa95359e019
RDX: 0000000000000000 RSI: 0000000000000020 RDI: 0000000000000000
RBP: 00007fa95363500c R08: 0000000000000000 R09: 0000000000000000
R10: 000000000000000e R11: 0000000000000246 R12: 0000000000000000
R13: 00007fa9538264e8 R14: 00007fa953826450 R15: 00007fff4d0e3998
 </TASK>
Modules linked in:
CR2: ffffc90013ccbfe8
---[ end trace 0000000000000000 ]---
RIP: 0010:write_comp_data+0x75/0x90 kernel/kcov.c:267
Code: 00 8b bf fc 16 00 00 48 8b 30 48 c1 e7 03 4c 8d 1c b5 00 00 00 00 4a 8d 14 dd 28 00 00 00 48 39 d7 72 bd 48 83 c6 01 48 89 30 <4c> 89 44 10 e0 4c 89 4c 10 e8 4c 89 54 10 f0 4a 89 4c d8 20 c3 cc
RSP: 0018:ffffc90005a57e78 EFLAGS: 00050257
RAX: ffffc90013ccc000 RBX: 0000000000000000 RCX: ffffffff824589a5
RDX: 0000000000000008 RSI: 0000000000000000 RDI: 0000000000400000
RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000002
R10: 0000000000000001 R11: fffffffffffffffc R12: 0000000000000020
R13: 0000000000000000 R14: 00007ffffffff000 R15: 0000000000000001
FS:  00007fa950b4b6c0(0000) GS:ffff888123de1000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffc90013ccbfe8 CR3: 000000005848c000 CR4: 00000000003526f0
----------------
Code disassembly (best guess):
   0:	00 8b bf fc 16 00    	add    %cl,0x16fcbf(%rbx)
   6:	00 48 8b             	add    %cl,-0x75(%rax)
   9:	30 48 c1             	xor    %cl,-0x3f(%rax)
   c:	e7 03                	out    %eax,$0x3
   e:	4c 8d 1c b5 00 00 00 	lea    0x0(,%rsi,4),%r11
  15:	00
  16:	4a 8d 14 dd 28 00 00 	lea    0x28(,%r11,8),%rdx
  1d:	00
  1e:	48 39 d7             	cmp    %rdx,%rdi
  21:	72 bd                	jb     0xffffffe0
  23:	48 83 c6 01          	add    $0x1,%rsi
  27:	48 89 30             	mov    %rsi,(%rax)
* 2a:	4c 89 44 10 e0       	mov    %r8,-0x20(%rax,%rdx,1) <-- trapping instruction
  2f:	4c 89 4c 10 e8       	mov    %r9,-0x18(%rax,%rdx,1)
  34:	4c 89 54 10 f0       	mov    %r10,-0x10(%rax,%rdx,1)
  39:	4a 89 4c d8 20       	mov    %rcx,0x20(%rax,%r11,8)
  3e:	c3                   	ret
  3f:	cc                   	int3


---
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Re: [syzbot] [kernel?] BUG: unable to handle kernel paging request in write_comp_data

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit:    704340f1cd0d Merge tag 'x86_urgent_for_7.3-rc4' of git://g..
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=13351925580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=8c5c3949d762a91f
dashboard link: https://syzkaller.appspot.com/bug?extid=237f670105a254a230d4
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11b875f9580000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+237f670105a254a230d4@syzkaller.appspotmail.com

BUG: unable to handle page fault for address: ffffc90003792fe8
#PF: supervisor write access in kernel mode
#PF: error_code(0x0002) - not-present page
PGD 1c000067 P4D 1c000067 PUD 1d695067 PMD 25aa1067 PTE 0
Oops: Oops: 0002 [#1] SMP KASAN NOPTI
CPU: 2 UID: 0 PID: 6034 Comm: syz-executor404 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:write_comp_data+0x7c/0xa0 kernel/kcov.c:263
Code: 00 8b bf 14 17 00 00 48 8b 30 48 c1 e7 03 4c 8d 1c b5 00 00 00 00 4a 8d 14 dd 28 00 00 00 48 39 d7 72 1b 48 83 c6 01 48 89 30 <4c> 89 44 10 e0 4c 89 4c 10 e8 4c 89 54 10 f0 4a 89 4c d8 20 e9 9b
RSP: 0018:ffffc900016cfec0 EFLAGS: 00010257
RAX: ffffc90003793000 RBX: 0000000000000000 RCX: ffffffff824af562
RDX: 0000000000000008 RSI: 0000000000000000 RDI: 0000000000002000
RBP: 0000000000000000 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000000 R11: fffffffffffffffc R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
FS:  000055556039d400(0000) GS:ffff8880d5d59000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffc90003792fe8 CR3: 0000000033822000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 __do_sys_rseq kernel/rseq.c:549 [inline]
 __se_sys_rseq kernel/rseq.c:547 [inline]
 __x64_sys_rseq+0xc2/0x2e0 kernel/rseq.c:547
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f4f6e875649
Code: c0 79 93 eb d5 48 8d 7c 1d 00 eb 99 0f 1f 44 00 00 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 d8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fffe975f1b8 EFLAGS: 00000246 ORIG_RAX: 000000000000014e
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f4f6e875649
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 00007f4f6e846000 R08: 0000000000000000 R09: 00000000000a8ca8
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fffe975f2e8
R13: 0000000000000002 R14: 00007f4f6e8f8cc0 R15: 0000000000000002
 </TASK>
Modules linked in:
CR2: ffffc90003792fe8
---[ end trace 0000000000000000 ]---
RIP: 0010:write_comp_data+0x7c/0xa0 kernel/kcov.c:263
Code: 00 8b bf 14 17 00 00 48 8b 30 48 c1 e7 03 4c 8d 1c b5 00 00 00 00 4a 8d 14 dd 28 00 00 00 48 39 d7 72 1b 48 83 c6 01 48 89 30 <4c> 89 44 10 e0 4c 89 4c 10 e8 4c 89 54 10 f0 4a 89 4c d8 20 e9 9b
RSP: 0018:ffffc900016cfec0 EFLAGS: 00010257
RAX: ffffc90003793000 RBX: 0000000000000000 RCX: ffffffff824af562
RDX: 0000000000000008 RSI: 0000000000000000 RDI: 0000000000002000
RBP: 0000000000000000 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000000 R11: fffffffffffffffc R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
FS:  000055556039d400(0000) GS:ffff8880d5d59000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffc90003792fe8 CR3: 0000000033822000 CR4: 0000000000352ef0
----------------
Code disassembly (best guess):
   0:	00 8b bf 14 17 00    	add    %cl,0x1714bf(%rbx)
   6:	00 48 8b             	add    %cl,-0x75(%rax)
   9:	30 48 c1             	xor    %cl,-0x3f(%rax)
   c:	e7 03                	out    %eax,$0x3
   e:	4c 8d 1c b5 00 00 00 	lea    0x0(,%rsi,4),%r11
  15:	00
  16:	4a 8d 14 dd 28 00 00 	lea    0x28(,%r11,8),%rdx
  1d:	00
  1e:	48 39 d7             	cmp    %rdx,%rdi
  21:	72 1b                	jb     0x3e
  23:	48 83 c6 01          	add    $0x1,%rsi
  27:	48 89 30             	mov    %rsi,(%rax)
* 2a:	4c 89 44 10 e0       	mov    %r8,-0x20(%rax,%rdx,1) <-- trapping instruction
  2f:	4c 89 4c 10 e8       	mov    %r9,-0x18(%rax,%rdx,1)
  34:	4c 89 54 10 f0       	mov    %r10,-0x10(%rax,%rdx,1)
  39:	4a 89 4c d8 20       	mov    %rcx,0x20(%rax,%r11,8)
  3e:	e9                   	.byte 0xe9
  3f:	9b                   	fwait


---
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

Re: [syzbot] [kernel?] BUG: unable to handle kernel paging request in write_comp_data

[Edward Adam Davis]

From: Edward Aadm Davis <eadavis@sina.com>

#syz test: upstream 704340f1cd0d

diff --git a/kernel/kcov.c b/kernel/kcov.c
index 35420f0ac524..479a84921833 100644
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -236,7 +236,7 @@ static void notrace write_comp_data(u64 type, u64 arg1, u64 arg2, u64 ip)
 {
 	struct task_struct *t;
 	u64 *area;
-	u64 count, start_index, end_pos, max_pos;
+	u64 count, start_index, end_pos, max_pos, tmp;
 
 	t = current;
 	if (!check_kcov_mode(KCOV_MODE_TRACE_CMP, t))
@@ -254,7 +254,9 @@ static void notrace write_comp_data(u64 type, u64 arg1, u64 arg2, u64 ip)
 	count = READ_ONCE(area[0]);
 
 	/* Every record is KCOV_WORDS_PER_CMP 64-bit words. */
-	start_index = 1 + count * KCOV_WORDS_PER_CMP;
+	if (check_mul_overflow(count, KCOV_WORDS_PER_CMP, &tmp))
+		return;
+	start_index = 1 + tmp;
 	end_pos = (start_index + KCOV_WORDS_PER_CMP) * sizeof(u64);
 	if (likely(end_pos <= max_pos)) {
 		/* See comment in __sanitizer_cov_trace_pc(). */

Re: [syzbot] [kernel?] BUG: unable to handle kernel paging request in write_comp_data

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+237f670105a254a230d4@syzkaller.appspotmail.com
Tested-by: syzbot+237f670105a254a230d4@syzkaller.appspotmail.com

Tested on:

commit:         704340f1 Merge tag 'x86_urgent_for_7.3-rc4' of git://g..
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=113a48c9580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=8c5c3949d762a91f
dashboard link: https://syzkaller.appspot.com/bug?extid=237f670105a254a230d4
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
patch:          https://syzkaller.appspot.com/x/patch.diff?x=13587df9580000

Note: testing is done by a robot and is best-effort only.

[PATCH] kcov: add a missing bound check in write_comp_data()

[Edward Adam Davis]

A missing bounds check in write_comp_data() can lead to an out-of-bounds read
or write in the adjacent memory area, since the start_index is not validated
before accessing area[] in the function later, potentially hitting:

BUG: unable to handle page fault for address: ffffc90003792fe8
RIP: 0010:write_comp_data+0x7c/0xa0 kernel/kcov.c:263
Call Trace:
 __do_sys_rseq kernel/rseq.c:549 [inline]
 __se_sys_rseq kernel/rseq.c:547 [inline]
 __x64_sys_rseq+0xc2/0x2e0 kernel/rseq.c:547

Fixes: ded97d2c2b2c ("kcov: support comparison operands collection")
Reported-by: syzbot+237f670105a254a230d4@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=237f670105a254a230d4
Tested-by: syzbot+237f670105a254a230d4@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <eadavis@sina.com>
---
 kernel/kcov.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/kcov.c b/kernel/kcov.c
index 35420f0ac524..479a84921833 100644
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -236,7 +236,7 @@ static void notrace write_comp_data(u64 type, u64 arg1, u64 arg2, u64 ip)
 {
 	struct task_struct *t;
 	u64 *area;
-	u64 count, start_index, end_pos, max_pos;
+	u64 count, start_index, end_pos, max_pos, tmp;
 
 	t = current;
 	if (!check_kcov_mode(KCOV_MODE_TRACE_CMP, t))
@@ -254,7 +254,9 @@ static void notrace write_comp_data(u64 type, u64 arg1, u64 arg2, u64 ip)
 	count = READ_ONCE(area[0]);
 
 	/* Every record is KCOV_WORDS_PER_CMP 64-bit words. */
-	start_index = 1 + count * KCOV_WORDS_PER_CMP;
+	if (check_mul_overflow(count, KCOV_WORDS_PER_CMP, &tmp))
+		return;
+	start_index = 1 + tmp;
 	end_pos = (start_index + KCOV_WORDS_PER_CMP) * sizeof(u64);
 	if (likely(end_pos <= max_pos)) {
 		/* See comment in __sanitizer_cov_trace_pc(). */
-- 
2.43.0