CVE-2023-52489 in Linux
Summary
by MITRE • 03/11/2024
In the Linux kernel, the following vulnerability has been resolved:
mm/sparsemem: fix race in accessing memory_section->usage
The below race is observed on a PFN which falls into the device memory region with the system memory configuration where PFN's are such that [ZONE_NORMAL ZONE_DEVICE ZONE_NORMAL]. Since normal zone start and end
pfn contains the device memory PFN's as well, the compaction triggered will try on the device memory PFN's too though they end up in NOP(because pfn_to_online_page() returns NULL for ZONE_DEVICE memory sections). When from other core, the section mappings are being removed for the ZONE_DEVICE region, that the PFN in question belongs to, on which compaction is currently being operated is resulting into the kernel crash with CONFIG_SPASEMEM_VMEMAP enabled. The crash logs can be seen at [1].
compact_zone() memunmap_pages ------------- --------------- __pageblock_pfn_to_page ...... (a)pfn_valid(): valid_section()//return true (b)__remove_pages()-> sparse_remove_section()-> section_deactivate(): [Free the array ms->usage and set
ms->usage = NULL] pfn_section_valid() [Access ms->usage which
is NULL]
NOTE: From the above it can be said that the race is reduced to between the pfn_valid()/pfn_section_valid() and the section deactivate with SPASEMEM_VMEMAP enabled.
The commit b943f045a9af("mm/sparse: fix kernel crash with pfn_section_valid check") tried to address the same problem by clearing the SECTION_HAS_MEM_MAP with the expectation of valid_section() returns false thus ms->usage is not accessed.
Fix this issue by the below steps:
a) Clear SECTION_HAS_MEM_MAP before freeing the ->usage.
b) RCU protected read side critical section will either return NULL when SECTION_HAS_MEM_MAP is cleared or can successfully access ->usage.
c) Free the ->usage with kfree_rcu() and set ms->usage = NULL. No attempt will be made to access ->usage after this as the SECTION_HAS_MEM_MAP is cleared thus valid_section() return false.
Thanks to David/Pavan for their inputs on this patch.
[1] https://lore.kernel.org/linux-mm/[email protected]/
On Snapdragon SoC, with the mentioned memory configuration of PFN's as [ZONE_NORMAL ZONE_DEVICE ZONE_NORMAL], we are able to see bunch of
issues daily while testing on a device farm.
For this particular issue below is the log. Though the below log is not directly pointing to the pfn_section_valid(){ ms->usage;}, when we
loaded this dump on T32 lauterbach tool, it is pointing.
[ 540.578056] Unable to handle kernel NULL pointer dereference at
virtual address 0000000000000000 [ 540.578068] Mem abort info:
[ 540.578070] ESR = 0x0000000096000005
[ 540.578073] EC = 0x25: DABT (current EL), IL = 32 bits
[ 540.578077] SET = 0, FnV = 0
[ 540.578080] EA = 0, S1PTW = 0
[ 540.578082] FSC = 0x05: level 1 translation fault
[ 540.578085] Data abort info:
[ 540.578086] ISV = 0, ISS = 0x00000005
[ 540.578088] CM = 0, WnR = 0
[ 540.579431] pstate: 82400005 (Nzcv daif +PAN -UAO +TCO -DIT -SSBSBTYPE=--)
[ 540.579436] pc : __pageblock_pfn_to_page+0x6c/0x14c
[ 540.579454] lr : compact_zone+0x994/0x1058
[ 540.579460] sp : ffffffc03579b510
[ 540.579463] x29: ffffffc03579b510 x28: 0000000000235800 x27:000000000000000c
[ 540.579470] x26: 0000000000235c00 x25: 0000000000000068 x24:ffffffc03579b640
[ 540.579477] x23: 0000000000000001 x22: ffffffc03579b660 x21:0000000000000000
[ 540.579483] x20: 0000000000235bff x19: ffffffdebf7e3940 x18:ffffffdebf66d140
[ 540.579489] x17: 00000000739ba063 x16: 00000000739ba063 x15:00000000009f4bff
[ 540.579495] x14: 0000008000000000 x13: 0000000000000000 x12:0000000000000001
[ 540.579501] x11: 0000000000000000 x10: 0000000000000000 x9 :ffffff897d2cd440
[ 540.579507] x8 : 0000000000000000 x7 : 0000000000000000 x6 :ffffffc03579b5b4
[ 540.579512] x5 : 0000000000027f25 x4 : ffffffc03579b5b8 x3 :0000000000000
---truncated---
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Analysis
by VulDB Data Team • 02/15/2025
The vulnerability described in CVE-2023-52489 resides within the Linux kernel's memory management subsystem, specifically in the sparse memory implementation. This flaw manifests as a race condition during memory compaction operations when dealing with device memory regions that are interleaved with normal memory zones, creating a configuration of [ZONE_NORMAL ZONE_DEVICE ZONE_NORMAL]. The issue arises due to improper synchronization between memory compaction processes and section deactivation mechanisms, particularly when CONFIG_SPARSEMEM_VMEMAP is enabled. The race condition occurs when the compaction process attempts to access memory section usage information while another kernel thread is simultaneously removing the section mappings for device memory regions, leading to a kernel crash through NULL pointer dereference.
The technical root cause involves the interaction between multiple kernel functions during memory management operations. The race condition specifically occurs between pfn_valid() and pfn_section_valid() function calls on one side, and section deactivation through sparse_remove_section() on the other. During compaction, __pageblock_pfn_to_page() calls pfn_valid() which in turn invokes valid_section() that returns true, allowing access to ms->usage. However, immediately afterward, __remove_pages() executes sparse_remove_section() which calls section_deactivate() and frees the ms->usage array while setting it to NULL. This creates a window where the compaction thread accesses freed memory, resulting in a null pointer dereference. The kernel crash occurs at __pageblock_pfn_to_page+0x6c/0x14c as indicated in the stack trace, where the memory access pattern leads to virtual address 0x0000000000000000.
This vulnerability impacts systems with specific memory configurations, particularly Snapdragon SoCs where device memory regions are present in the memory map. The issue is classified as a race condition affecting memory management operations and is aligned with CWE-362, which describes race conditions in concurrent programming. The problem directly relates to the ATT&CK technique T1059.006, which involves kernel-level code execution through memory management flaws, and T1070.004, which covers system binary modification through kernel vulnerabilities. The vulnerability demonstrates the complexity of managing memory sections in sparse memory configurations and the critical importance of proper synchronization mechanisms when dealing with concurrent memory operations in kernel space.
The fix implemented addresses the race condition by reordering the operations to clear the SECTION_HAS_MEM_MAP flag before freeing the memory section usage array. This ensures that subsequent calls to valid_section() will return false, preventing access to the freed memory structure. The solution employs RCU (Read-Copy-Update) protected read-side critical sections that either return NULL when SECTION_HAS_MEM_MAP is cleared or successfully access the usage array before it gets freed. Additionally, the fix uses kfree_rcu() to properly free the usage array and sets ms->usage = NULL to prevent any further access attempts. This approach aligns with the kernel's memory management best practices and follows the established pattern of clearing flags before freeing associated resources to prevent race conditions. The mitigation ensures that memory compaction operations cannot access freed memory structures while maintaining the integrity of the sparse memory subsystem and preventing kernel crashes that would otherwise occur during normal system operation.