linux-kernel - [PATCH 2/3] x86/entry/64: Don't compile ignore

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Date:   Mon,  1 Jul 2019 20:43:20 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, "Bae, Chang Seok" <chang.seok.bae@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>
Subject: [PATCH 2/3] x86/entry/64: Don't compile ignore_sysret if 32-bit emulation is enabled

It's only used if !CONFIG_IA32_EMULATION, so disable it in normal
configs.  This will save a few bytes of text and reduce confusion.

Cc: "Bae, Chang Seok" <chang.seok.bae@...el.com>
Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 arch/x86/entry/entry_64.S | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 7f9f5119d6b1..54b1b0468b2b 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -1743,11 +1743,17 @@ nmi_restore:
 	iretq
 END(nmi)
 
+#ifndef CONFIG_IA32_EMULATION
+/*
+ * This handles SYSCALL from 32-bit code.  There is no way to program
+ * MSRs to fully disable 32-bit SYSCALL.
+ */
 ENTRY(ignore_sysret)
 	UNWIND_HINT_EMPTY
 	mov	$-ENOSYS, %eax
 	sysret
 END(ignore_sysret)
+#endif
 
 ENTRY(rewind_stack_do_exit)
 	UNWIND_HINT_FUNC
-- 
2.21.0