CVE-2022-49214 powerpc/64s: Don't use DSISR for SLB faults
A Linux kernel bug on PowerPC 64s systems causes incorrect fault reporting for SLB faults, potentially leading to kernel crashes or denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2022-49214?
CVE-2022-49214 is a medium-severity vulnerability in Linux kernel, published on 26 Feb 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
powerpc/64s: Don't use DSISR for SLB faults
Since commit 46ddcb3950a2 ("powerpc/mm: Show if a bad page fault on data is read or write.") we use page_fault_is_write(regs->dsisr) in __bad_page_fault() to determine if the fault is for a read or write, and change the message printed accordingly.
But SLB faults, aka Data Segment Interrupts, don't set DSISR (Data Storage Interrupt Status Register) to a useful value. All ISA versions from v2.03 through v3.1 specify that the Data Segment Interrupt sets DSISR "to an undefined value". As far as I can see there's no mention of SLB faults setting DSISR in any BookIV content either.
This manifests as accesses that should be a read being incorrectly reported as writes, for example, using the xmon "dump" command:
0:mon> d 0x5deadbeef0000000 5deadbeef0000000 [359526.415354][ C6] BUG: Unable to handle kernel data access on write at 0x5deadbeef0000000 [359526.415611][ C6] Faulting instruction address: 0xc00000000010a300 cpu 0x6: Vector: 380 (Data SLB Access) at [c00000000ffbf400] pc: c00000000010a300: mread+0x90/0x190
If we disassemble the PC, we see a load instruction:
0:mon> di c00000000010a300 c00000000010a300 89490000 lbz r10,0(r9)
We can also see in exceptions-64s.S that the data_access_slb block doesn't set IDSISR=1, which means it doesn't load DSISR into pt_regs. So the value we're using to determine if the fault is a read/write is some stale value in pt_regs from a previous page fault.
Rework the printing logic to separate the SLB fault case out, and only print read/write in the cases where we can determine it.
The result looks like eg:
0:mon> d 0x5deadbeef0000000 5deadbeef0000000 [ 721.779525][ C6] BUG: Unable to handle kernel data access at 0x5deadbeef0000000 [ 721.779697][ C6] Faulting instruction address: 0xc00000000014cbe0 cpu 0x6: Vector: 380 (Data SLB Access) at [c00000000ffbf390]
0:mon> d 0 0000000000000000 [ 742.793242][ C6] BUG: Kernel NULL pointer dereference at 0x00000000 [ 742.793316][ C6] Faulting instruction address: 0xc00000000014cbe0 cpu 0x6: Vector: 380 (Data SLB Access) at [c00000000ffbf390]
Weakness: CWE-476
Which versions are affected by CVE-2022-49214?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2022-49214?
Apply the vendor's patch.
Is CVE-2022-49214 being exploited?
There is no known exploitation of CVE-2022-49214 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as DEBIAN-CVE-2022-49214, GHSA-8jrg-738q-v5mw, ROOT-OS-DEBIAN-11-CVE-2022-49214, UBUNTU-CVE-2022-49214.