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    Subject[PATCH 5.18 15/70] x86/ftrace: Use alternative RET encoding
    Date
    From: Peter Zijlstra <peterz@infradead.org>

    commit 1f001e9da6bbf482311e45e48f53c2bd2179e59c upstream.

    Use the return thunk in ftrace trampolines, if needed.

    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Signed-off-by: Borislav Petkov <bp@suse.de>
    Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>
    Signed-off-by: Borislav Petkov <bp@suse.de>
    Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/x86/kernel/ftrace.c | 7 +++++--
    1 file changed, 5 insertions(+), 2 deletions(-)

    --- a/arch/x86/kernel/ftrace.c
    +++ b/arch/x86/kernel/ftrace.c
    @@ -303,7 +303,7 @@ union ftrace_op_code_union {
    } __attribute__((packed));
    };

    -#define RET_SIZE 1 + IS_ENABLED(CONFIG_SLS)
    +#define RET_SIZE (IS_ENABLED(CONFIG_RETPOLINE) ? 5 : 1 + IS_ENABLED(CONFIG_SLS))

    static unsigned long
    create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
    @@ -359,7 +359,10 @@ create_trampoline(struct ftrace_ops *ops
    goto fail;

    ip = trampoline + size;
    - memcpy(ip, retq, RET_SIZE);
    + if (cpu_feature_enabled(X86_FEATURE_RETHUNK))
    + __text_gen_insn(ip, JMP32_INSN_OPCODE, ip, &__x86_return_thunk, JMP32_INSN_SIZE);
    + else
    + memcpy(ip, retq, sizeof(retq));

    /* No need to test direct calls on created trampolines */
    if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) {

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