Re: [PATCH] KVM: x86: Ensure liveliness of nested VM-Enter fail tracepoint message

[Paolo Bonzini <pbonzini@redhat.com>]

On 07/06/21 20:48, Steven Rostedt wrote:
> On Mon,  7 Jun 2021 10:57:48 -0700
> Sean Christopherson <seanjc@google.com> wrote:
> 
>> 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
>> can't 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
>>
>> Cc: Steven Rostedt <rostedt@goodmis.org>
>> Fixes: 380e0055bc7e ("KVM: nVMX: trace nested VM-Enter failures detected by H/W")
>> Signed-off-by: Sean Christopherson <seanjc@google.com>
>> ---
>>
> 
> Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
> 
> -- Steve
> 

Queued, thanks.

Paolo