[PATCH] iommu/vt-d: debugfs: fix legacy mode page table dump logic
From: Vineeth Pillai (Google)
Date: Thu Aug 14 2025 - 12:34:48 EST
In legacy mode, SSPTPTR is ignored if TT is not 00b or 01b. SSPTPTR
maybe uninitialized or zero in that case and may cause oops like:
Oops: general protection fault, probably for non-canonical address 0xf00087d3f000f000: 0000 [#1] SMP NOPTI
CPU: 2 UID: 0 PID: 786 Comm: cat Not tainted 6.16.0 #191 PREEMPT(voluntary)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.17.0-5.fc42 04/01/2014
RIP: 0010:pgtable_walk_level+0x98/0x150
RSP: 0018:ffffc90000f279c0 EFLAGS: 00010206
RAX: 0000000040000000 RBX: ffffc90000f27ab0 RCX: 000000000000001e
RDX: 0000000000000003 RSI: f00087d3f000f000 RDI: f00087d3f0010000
RBP: ffffc90000f27a00 R08: ffffc90000f27a98 R09: 0000000000000002
R10: 0000000000000000 R11: 0000000000000000 R12: f00087d3f000f000
R13: 0000000000000000 R14: 0000000040000000 R15: ffffc90000f27a98
FS: 0000764566dcb740(0000) GS:ffff8881f812c000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000764566d44000 CR3: 0000000109d81003 CR4: 0000000000772ef0
PKRU: 55555554
Call Trace:
<TASK>
pgtable_walk_level+0x88/0x150
domain_translation_struct_show.isra.0+0x2d9/0x300
dev_domain_translation_struct_show+0x20/0x40
seq_read_iter+0x12d/0x490
...
Avoid walking the page table if TT is not 00b or 01b.
Signed-off-by: Vineeth Pillai (Google) <vineeth@xxxxxxxxxxxxxxx>
---
drivers/iommu/intel/debugfs.c | 17 +++++++++++++++--
1 file changed, 15 insertions(+), 2 deletions(-)
diff --git a/drivers/iommu/intel/debugfs.c b/drivers/iommu/intel/debugfs.c
index affbf4a1558de..5aa7f46a420b5 100644
--- a/drivers/iommu/intel/debugfs.c
+++ b/drivers/iommu/intel/debugfs.c
@@ -435,8 +435,21 @@ static int domain_translation_struct_show(struct seq_file *m,
}
pgd &= VTD_PAGE_MASK;
} else { /* legacy mode */
- pgd = context->lo & VTD_PAGE_MASK;
- agaw = context->hi & 7;
+ u8 tt = (u8)(context->lo & GENMASK_ULL(3, 2)) >> 2;
+
+ /*
+ * According to Translation Type(TT),
+ * get the page table pointer(SSPTPTR).
+ */
+ switch (tt) {
+ case CONTEXT_TT_MULTI_LEVEL:
+ case CONTEXT_TT_DEV_IOTLB:
+ pgd = context->lo & VTD_PAGE_MASK;
+ agaw = context->hi & 7;
+ break;
+ default:
+ goto iommu_unlock;
+ }
}
seq_printf(m, "Device %04x:%02x:%02x.%x ",
--
2.50.1