On Thu, 2018-02-22 at 01:05 +0100, Daniel Borkmann wrote:
...
> +/* Instead of plain jmp %rax, we emit a retpoline to control
> + * speculative execution for the indirect branch.
> + */
> +static void emit_retpoline_rax_trampoline(u8 **pprog)
> +{
> + u8 *prog = *pprog;
> + int cnt = 0;
> +
> + EMIT1_off32(0xE8, 7); /* callq <set_up_target> */
> + /* capture_spec: */
> + EMIT2(0xF3, 0x90); /* pause */
> + EMIT3(0x0F, 0xAE, 0xE8); /* lfence */
> + EMIT2(0xEB, 0xF9); /* jmp <capture_spec> */
> + /* set_up_target: */
> + EMIT4(0x48, 0x89, 0x04, 0x24); /* mov %rax,(%rsp) */
> + EMIT1(0xC3); /* retq */
> +
> + BUILD_BUG_ON(cnt != RETPOLINE_SIZE);
> + *pprog = prog;
You might define the actual code sequence (and length) in
arch/x86/include/asm/nospec-branch.h
If we need to adjust code sequences for RETPOLINE, then we wont
forget/miss that arch/x86/net/bpf_jit_comp.c had it hard-coded.
Thanks Daniel.
