CVE-2021-47262

In the Linux kernel, the following vulnerability has been resolved:

KVM: x86: Ensure liveliness of nested VM-Enter fail tracepoint message

Use the __string() machinery provided by the tracing subystem to make a copy of the string literals consumed by the nested VM-Enter failed tracepoint. A complete copy is necessary to ensure that the tracepoint cant outlive the data/memory it consumes and deference stale memory.

Because the tracepoint itself is defined by kvm, if kvm-intel and/or kvm-amd are built as modules, the memory holding the string literals defined by the vendor modules will be freed when the module is unloaded, whereas the tracepoint and its data in the ring buffer will live until kvm is unloaded (or indefinitely if kvm is built-in).

This bug has existed since the tracepoint was added, but was recently exposed by a new check in tracing to detect exactly this type of bug.

fmt: %s%s current_buffer: vmx_dirty_log_t-140127 [003] …. kvm_nested_vmenter_failed: WARNING: CPU: 3 PID: 140134 at kernel/trace/trace.c:3759 trace_check_vprintf+0x3be/0x3e0 CPU: 3 PID: 140134 Comm: less Not tainted 5.13.0-rc1-ce2e73ce600a-req #184 Hardware name: ASUS Q87M-E/Q87M-E, BIOS 1102 03/03/2014 RIP: 0010:trace_check_vprintf+0x3be/0x3e0 Code: <0f> 0b 44 8b 4c 24 1c e9 a9 fe ff ff c6 44 02 ff 00 49 8b 97 b0 20 RSP: 0018:ffffa895cc37bcb0 EFLAGS: 00010282 RAX: 0000000000000000 RBX: ffffa895cc37bd08 RCX: 0000000000000027 RDX: 0000000000000027 RSI: 00000000ffffdfff RDI: ffff9766cfad74f8 RBP: ffffffffc0a041d4 R08: ffff9766cfad74f0 R09: ffffa895cc37bad8 R10: 0000000000000001 R11: 0000000000000001 R12: ffffffffc0a041d4 R13: ffffffffc0f4dba8 R14: 0000000000000000 R15: ffff976409f2c000 FS: 00007f92fa200740(0000) GS:ffff9766cfac0000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000559bd11b0000 CR3: 000000019fbaa002 CR4: 00000000001726e0 Call Trace: trace_event_printf+0x5e/0x80 trace_raw_output_kvm_nested_vmenter_failed+0x3a/0x60 [kvm] print_trace_line+0x1dd/0x4e0 s_show+0x45/0x150 seq_read_iter+0x2d5/0x4c0 seq_read+0x106/0x150 vfs_read+0x98/0x180 ksys_read+0x5f/0xe0 do_syscall_64+0x40/0xb0 entry_SYSCALL_64_after_hwframe+0x44/0xae

Affected Software

References

• https://git.kernel.org/stable/c/796d3bd4ac9316e70c181189318cd2bd98af34bc
• https://git.kernel.org/stable/c/9fb088ce13bc3c59a51260207b487db3e556f275
• https://git.kernel.org/stable/c/d046f724bbd725a24007b7e52b2d675249870888
• https://git.kernel.org/stable/c/f31500b0d437a2464ca5972d8f5439e156b74960