// For flags

CVE-2022-49214

powerpc/64s: Don't use DSISR for SLB faults

Time Line
Published
2024-03-19
Updated
2024-03-19
Firt exploit
2024-03-19
Overview
Descriptions (1)
MITRE
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EPSS
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Vendors (1)
linux
Products (1)
linux_kernel
Versions (4)
>= 5.5 < 5.15.33, >= 5.5 < 5.16.19, >= 5.5 < 5.17.2, >= 5.5 < 5.18
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References (5)
General (1)
kernel
Exploits & POcs (-)
Patches (4)
kernel
Advisories (-)
Summary
Descriptions

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]

*Credits: N/A
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Timeline
  • 2025-02-26 CVE Reserved
  • 2025-02-26 CVE Published
  • 2025-02-26 CVE Updated
  • ---------- EPSS Updated
  • ---------- Exploited in Wild
  • ---------- KEV Due Date
  • ---------- First Exploit
CWE
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Affected Vendors, Products, and Versions
Vendor Product Version Other Status
Vendor Product Version Other Status <-- --> Vendor Product Version Other Status
Linux
Search vendor "Linux"
 Linux Kernel
Search vendor "Linux" for product "Linux Kernel"
 >= 5.5 < 5.15.33
Search vendor "Linux" for product "Linux Kernel" and version " >= 5.5 < 5.15.33"
en
Affected
Linux
Search vendor "Linux"
 Linux Kernel
Search vendor "Linux" for product "Linux Kernel"
 >= 5.5 < 5.16.19
Search vendor "Linux" for product "Linux Kernel" and version " >= 5.5 < 5.16.19"
en
Affected
Linux
Search vendor "Linux"
 Linux Kernel
Search vendor "Linux" for product "Linux Kernel"
 >= 5.5 < 5.17.2
Search vendor "Linux" for product "Linux Kernel" and version " >= 5.5 < 5.17.2"
en
Affected
Linux
Search vendor "Linux"
 Linux Kernel
Search vendor "Linux" for product "Linux Kernel"
 >= 5.5 < 5.18
Search vendor "Linux" for product "Linux Kernel" and version " >= 5.5 < 5.18"
en
Affected