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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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