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SubjectRe: [PATCH v22 8/8] x86/vdso: Add ENDBR64 to __vdso_sgx_enter_enclave
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On 3/10/2021 2:39 PM, Jarkko Sakkinen wrote:
> On Wed, Mar 10, 2021 at 02:05:19PM -0800, Yu-cheng Yu wrote:
>> When CET is enabled, __vdso_sgx_enter_enclave() needs an endbr64
>> in the beginning of the function.
>
> OK.
>
> What you should do is to explain what it does and why it's needed.
>

The endbr marks a branch target. Without the "no-track" prefix, if an
indirect call/jmp reaches a non-endbr opcode, a control-protection fault
is raised. Usually endbr's are inserted by the compiler. For assembly,
these have to be put in manually. I will add this in the commit log if
there is another revision. Thanks!

--
Yu-cheng

>>
>> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
>> Cc: Andy Lutomirski <luto@kernel.org>
>> Cc: Dave Hansen <dave.hansen@linux.intel.com>
>> Cc: Jarkko Sakkinen <jarkko@kernel.org>
>> ---
>> arch/x86/entry/vdso/vsgx.S | 3 +++
>> 1 file changed, 3 insertions(+)
>>
>> diff --git a/arch/x86/entry/vdso/vsgx.S b/arch/x86/entry/vdso/vsgx.S
>> index 86a0e94f68df..a70d4d09f713 100644
>> --- a/arch/x86/entry/vdso/vsgx.S
>> +++ b/arch/x86/entry/vdso/vsgx.S
>> @@ -27,6 +27,9 @@
>> SYM_FUNC_START(__vdso_sgx_enter_enclave)
>> /* Prolog */
>> .cfi_startproc
>> +#ifdef CONFIG_X86_CET
>> + endbr64
>> +#endif
>> push %rbp
>> .cfi_adjust_cfa_offset 8
>> .cfi_rel_offset %rbp, 0
>> --
>> 2.21.0
>>
>>
>
> /Jarkko
>

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