Re: [PATCH 9/9] bpf,x86: Respect X86_FEATURE_RETPOLINE*

[Peter Zijlstra <peterz@infradead.org>]

On Thu, Oct 14, 2021 at 11:46:11AM +0200, Peter Zijlstra wrote:
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -396,6 +396,37 @@ static int get_pop_bytes(bool *callee_re
>  	return bytes;
>  }
>  
> +#define EMIT_LFENCE()	EMIT3(0x0F, 0xAE, 0xE8)
> +
> +#ifdef CONFIG_RETPOLINE
> +#define INDIRECT_SIZE (5)

Bah, that should be:

#define INDIRECT_SIZE	(2 + 3*cpu_feature_enabled(X86_FEATURE_RETPOLINE))

> +#else
> +#define INDIRECT_SIZE (2)
> +#endif
> +
> +static void emit_indirect_jump(u8 **pprog, int reg, u8 *ip)
> +{
> +	static const void *reg_thunk[] = {
> +#undef GEN
> +#define GEN(reg) __x86_indirect_thunk_ ## reg,
> +#include <asm/GEN-for-each-reg.h>
> +	};
> +
> +	u8 *prog = *pprog;
> +
> +#ifdef CONFIG_RETPOLINE
> +	if (cpu_feature_enabled(X86_FEATURE_RETPOLINE_AMD)) {
> +		EMIT_LFENCE();
> +		EMIT2(0xFF, 0xE0 + reg);
> +	} else if (cpu_feature_enabled(X86_FEATURE_RETPOLINE)) {
> +		emit_jump(&prog, reg_thunk[reg], ip);
> +	} else
> +#endif
> +	EMIT2(0xFF, 0xE0 + reg);
> +
> +	*pprog = prog;
> +}