From: Josh Poimboeuf <jpoimboe@redhat.com>
Date: Mon, 15 Jul 2019 16:51:39 +0000 (-0500)
Subject: x86/entry/64: Use JMP instead of JMPQ
X-Git-Tag: v4.4.189~2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=967858f2f222dd140429c70d855e85dafcc89c29;p=thirdparty%2Fkernel%2Fstable.git

x86/entry/64: Use JMP instead of JMPQ

commit 64dbc122b20f75183d8822618c24f85144a5a94d upstream.

Somehow the swapgs mitigation entry code patch ended up with a JMPQ
instruction instead of JMP, where only the short jump is needed.  Some
assembler versions apparently fail to optimize JMPQ into a two-byte JMP
when possible, instead always using a 7-byte JMP with relocation.  For
some reason that makes the entry code explode with a #GP during boot.

Change it back to "JMP" as originally intended.

Fixes: 18ec54fdd6d1 ("x86/speculation: Prepare entry code for Spectre v1 swapgs mitigations")
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
[bwh: Backported to 4.4: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 0baac4a1dc11c..afb805b0148b1 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -567,7 +567,7 @@ END(irq_entries_start)
 #ifdef CONFIG_CONTEXT_TRACKING
 	call enter_from_user_mode
 #endif
-	jmpq	2f
+	jmp	2f
 1:
 	FENCE_SWAPGS_KERNEL_ENTRY
 2: