[syzbot] [iommu?] KMSAN: uninit-value in pfn_reader_next

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: c072629f05d7 Merge tag 'v6.19-p4' of git://git.kernel.org/..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1716005a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=8bf02b9e495b9fcd
dashboard link: https://syzkaller.appspot.com/bug?extid=df28076a30d726933015
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1436b79a580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=15a63d22580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/b6b938ba4a72/disk-c072629f.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/bb1384b011b2/vmlinux-c072629f.xz
kernel image: https://storage.googleapis.com/syzbot-assets/1dd4bb2f206e/bzImage-c072629f.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+df2807...@syzkaller.appspotmail.com

iommufd_mock iommufd_mock0: Adding to iommu group 0
=====================================================
BUG: KMSAN: uninit-value in batch_add_pfn_num drivers/iommu/iommufd/pages.c:365 [inline]
BUG: KMSAN: uninit-value in batch_add_pfn drivers/iommu/iommufd/pages.c:398 [inline]
BUG: KMSAN: uninit-value in batch_from_pages drivers/iommu/iommufd/pages.c:658 [inline]
BUG: KMSAN: uninit-value in pfn_reader_fill_span drivers/iommu/iommufd/pages.c:1220 [inline]
BUG: KMSAN: uninit-value in pfn_reader_next+0x1d5a/0x3e50 drivers/iommu/iommufd/pages.c:1247
batch_add_pfn_num drivers/iommu/iommufd/pages.c:365 [inline]
batch_add_pfn drivers/iommu/iommufd/pages.c:398 [inline]
batch_from_pages drivers/iommu/iommufd/pages.c:658 [inline]
pfn_reader_fill_span drivers/iommu/iommufd/pages.c:1220 [inline]
pfn_reader_next+0x1d5a/0x3e50 drivers/iommu/iommufd/pages.c:1247
pfn_reader_first+0xbcf/0xee0 drivers/iommu/iommufd/pages.c:1354
iopt_area_fill_domains+0x202/0x1590 drivers/iommu/iommufd/pages.c:1917
iopt_fill_domains_pages drivers/iommu/iommufd/io_pagetable.c:359 [inline]
iopt_map_pages+0x1ba5/0x2130 drivers/iommu/iommufd/io_pagetable.c:387
iopt_map_common+0x224/0x610 drivers/iommu/iommufd/io_pagetable.c:425
iopt_map_user_pages+0x148/0x1c0 drivers/iommu/iommufd/io_pagetable.c:466
iommufd_ioas_map+0x6a2/0x9b0 drivers/iommu/iommufd/ioas.c:270
iommufd_fops_ioctl+0x82a/0x9e0 drivers/iommu/iommufd/main.c:533
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0x23c/0x400 fs/ioctl.c:583
__x64_sys_ioctl+0x97/0xe0 fs/ioctl.c:583
x64_sys_call+0x18a7/0x3e70 arch/x86/include/generated/asm/syscalls_64.h:17
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xc9/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Local variable pfns created at:
iopt_area_fill_domains+0x5c/0x1590 drivers/iommu/iommufd/pages.c:1900
iopt_fill_domains_pages drivers/iommu/iommufd/io_pagetable.c:359 [inline]
iopt_map_pages+0x1ba5/0x2130 drivers/iommu/iommufd/io_pagetable.c:387

CPU: 0 UID: 0 PID: 6065 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/13/2026
=====================================================


---
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[syzbot]

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***

Subject: [PATCH] iommufd: Initialize pfn_reader in iopt_area_fill_domains()
Author: karti...@gmail.com


#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

KMSAN reported an uninitialized value in batch_add_pfn_num() when
accessing batch->npfns[] and batch->pfns[] arrays. This occurs because
struct pfn_reader pfns was declared without initialization, leaving
the embedded pfn_batch structure and its arrays uninitialized.

Initialize pfns to zero to ensure all fields and embedded structures
start in a known state.

Reported-by: syzbot+df2807...@syzkaller.appspotmail.com
Signed-off-by: Deepanshu Kartikey <karti...@gmail.com>
---
drivers/iommu/iommufd/pages.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iommu/iommufd/pages.c b/drivers/iommu/iommufd/pages.c
index dbe51ecb9a20..a07373cf013c 100644
--- a/drivers/iommu/iommufd/pages.c
+++ b/drivers/iommu/iommufd/pages.c
@@ -1897,7 +1897,7 @@ int iopt_area_fill_domains(struct iopt_area *area, struct iopt_pages *pages)
unsigned long done_all_end_index;
struct iommu_domain *domain;
unsigned long unmap_index;
- struct pfn_reader pfns;
+ struct pfn_reader pfns = {};
unsigned long index;
int rc;

--
2.43.0

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
KMSAN: uninit-value in batch_from_domain

=====================================================
BUG: KMSAN: uninit-value in batch_add_pfn_num drivers/iommu/iommufd/pages.c:365 [inline]
BUG: KMSAN: uninit-value in batch_add_pfn drivers/iommu/iommufd/pages.c:398 [inline]

BUG: KMSAN: uninit-value in batch_from_domain+0xe8c/0x1010 drivers/iommu/iommufd/pages.c:425

batch_add_pfn_num drivers/iommu/iommufd/pages.c:365 [inline]
batch_add_pfn drivers/iommu/iommufd/pages.c:398 [inline]

batch_from_domain+0xe8c/0x1010 drivers/iommu/iommufd/pages.c:425
iopt_area_unpin_domain drivers/iommu/iommufd/pages.c:1687 [inline]
__iopt_area_unfill_domain+0xccf/0x1b90 drivers/iommu/iommufd/pages.c:1773
iopt_area_unfill_domain+0x100/0x140 drivers/iommu/iommufd/pages.c:1828
iopt_unfill_domain drivers/iommu/iommufd/io_pagetable.c:1025 [inline]
iopt_table_remove_domain+0xada/0x1010 drivers/iommu/iommufd/io_pagetable.c:1269
iommufd_hwpt_paging_destroy+0x21e/0x540 drivers/iommu/iommufd/hw_pagetable.c:30
iommufd_object_remove+0x4c8/0x6c0 drivers/iommu/iommufd/main.c:273
iommufd_object_put_and_try_destroy drivers/iommu/iommufd/iommufd_private.h:268 [inline]
iommufd_hw_pagetable_put drivers/iommu/iommufd/iommufd_private.h:461 [inline]
iommufd_hw_pagetable_detach+0x6e3/0xa10 drivers/iommu/iommufd/device.c:714
iommufd_device_detach+0x38/0xe0 drivers/iommu/iommufd/device.c:1059
iommufd_selftest_destroy+0x9e/0x100 drivers/iommu/iommufd/selftest.c:1951
iommufd_fops_release+0x1e0/0x5f0 drivers/iommu/iommufd/main.c:361
__fput+0x60e/0x1050 fs/file_table.c:468
____fput+0x25/0x30 fs/file_table.c:496
task_work_run+0x208/0x2b0 kernel/task_work.c:233
resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
__exit_to_user_mode_loop kernel/entry/common.c:44 [inline]
exit_to_user_mode_loop+0x2ff/0x1b20 kernel/entry/common.c:75
__exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
syscall_exit_to_user_mode_work include/linux/entry-common.h:159 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:194 [inline]
do_syscall_64+0x1d7/0xf80 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Local variable batch created at:
__iopt_area_unfill_domain+0xa8/0x1b90 drivers/iommu/iommufd/pages.c:1738
iopt_area_unfill_domain+0x100/0x140 drivers/iommu/iommufd/pages.c:1828

CPU: 0 UID: 0 PID: 6581 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(voluntary)

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/13/2026
=====================================================

Tested on:

commit: 62085877 Merge tag 'kbuild-fixes-6.19-2' of git://git...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1642c452580000

kernel config: https://syzkaller.appspot.com/x/.config?x=8bf02b9e495b9fcd
dashboard link: https://syzkaller.appspot.com/bug?extid=df28076a30d726933015
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

patch: https://syzkaller.appspot.com/x/patch.diff?x=158cc452580000

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-...@vger.kernel.org, syzkall...@googlegroups.com.

***

Subject: [PATCH] iommufd: Initialize batch structures in map/unmap paths

Author: karti...@gmail.com


#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

KMSAN reported uninitialized values in batch processing for both the
map and unmap paths:

1. In iopt_area_fill_domains(), struct pfn_reader pfns was used
uninitialized, causing warnings in batch_add_pfn_num() when

accessing batch->npfns[] and batch->pfns[] arrays.

2. In __iopt_area_unfill_domain(), struct pfn_batch batch was used
uninitialized, causing warnings in batch_from_domain() when
accessing the same arrays.

Although some initialization functions are called on these structures,
they do not initialize all fields, leaving arrays and padding bytes
uninitialized.

Initialize both structures to zero to ensure all fields start in a

known state.

Reported-by: syzbot+df2807...@syzkaller.appspotmail.com
Signed-off-by: Deepanshu Kartikey <karti...@gmail.com>
---

drivers/iommu/iommufd/pages.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/iommufd/pages.c b/drivers/iommu/iommufd/pages.c
index dbe51ecb9a20..8c7681192a07 100644
--- a/drivers/iommu/iommufd/pages.c
+++ b/drivers/iommu/iommufd/pages.c
@@ -1735,7 +1735,7 @@ static void __iopt_area_unfill_domain(struct iopt_area *area,
unsigned long start_index = iopt_area_index(area);
unsigned long unmapped_end_index = start_index;
u64 backup[BATCH_BACKUP_SIZE];
- struct pfn_batch batch;
+ struct pfn_batch batch = {};

lockdep_assert_held(&pages->mutex);

[syzbot]

Hello,

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

Reported-by: syzbot+df2807...@syzkaller.appspotmail.com
Tested-by: syzbot+df2807...@syzkaller.appspotmail.com

Tested on:

commit: 62085877 Merge tag 'kbuild-fixes-6.19-2' of git://git...
git tree: upstream

console output: https://syzkaller.appspot.com/x/log.txt?x=1246bd22580000

kernel config: https://syzkaller.appspot.com/x/.config?x=8bf02b9e495b9fcd
dashboard link: https://syzkaller.appspot.com/bug?extid=df28076a30d726933015
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

patch: https://syzkaller.appspot.com/x/patch.diff?x=1007805a580000

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