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

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
......@@ -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;
......
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