Commit d77cfe59 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Borislav Petkov
Browse files

x86/bpf: Use alternative RET encoding 



Use the return thunk in eBPF generated code, if needed.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Reviewed-by: default avatarJosh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
parent 1f001e9d

arch/x86/net/bpf_jit_comp.c

+17 −2
Original line number Diff line number Diff line
@@ -425,6 +425,21 @@ static void emit_indirect_jump(u8 **pprog, int reg, u8 *ip) 
	*pprog = prog;

}



static void emit_return(u8 **pprog, u8 *ip)

{

	u8 *prog = *pprog;



	if (cpu_feature_enabled(X86_FEATURE_RETHUNK)) {

		emit_jump(&prog, &__x86_return_thunk, ip);

	} else {

		EMIT1(0xC3);		/* ret */

		if (IS_ENABLED(CONFIG_SLS))

			EMIT1(0xCC);	/* int3 */

	}



	*pprog = prog;

}



/*

 * Generate the following code:

 *
@@ -1685,7 +1700,7 @@ st: if (is_imm8(insn->off)) 
			ctx->cleanup_addr = proglen;

			pop_callee_regs(&prog, callee_regs_used);

			EMIT1(0xC9);         /* leave */

			EMIT1(0xC3);         /* ret */

			emit_return(&prog, image + addrs[i - 1] + (prog - temp));

			break;



		default:
@@ -2188,7 +2203,7 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i 
	if (flags & BPF_TRAMP_F_SKIP_FRAME)

		/* skip our return address and return to parent */

		EMIT4(0x48, 0x83, 0xC4, 8); /* add rsp, 8 */

	EMIT1(0xC3); /* ret */

	emit_return(&prog, prog);

	/* Make sure the trampoline generation logic doesn't overflow */

	if (WARN_ON_ONCE(prog > (u8 *)image_end - BPF_INSN_SAFETY)) {

		ret = -EFAULT;