linux-kernel - [PATCH 5.15 34/89] x86/bpf: Use alternative RET encoding

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Message-Id: <20220722091135.272342062@linuxfoundation.org>
Date:   Fri, 22 Jul 2022 11:11:08 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Borislav Petkov <bp@...e.de>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Thadeu Lima de Souza Cascardo <cascardo@...onical.com>
Subject: [PATCH 5.15 34/89] x86/bpf: Use alternative RET encoding

From: Peter Zijlstra <peterz@...radead.org>

commit d77cfe594ad50e0bf95d457e02ccd578791b2a15 upstream.

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

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Borislav Petkov <bp@...e.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@...nel.org>
Signed-off-by: Borislav Petkov <bp@...e.de>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@...onical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/net/bpf_jit_comp.c |   19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -406,6 +406,21 @@ static void emit_indirect_jump(u8 **ppro
 	*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:
  *
@@ -1681,7 +1696,7 @@ emit_jmp:
 			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:
@@ -2127,7 +2142,7 @@ int arch_prepare_bpf_trampoline(struct b
 	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;