Re: Avoid speculative indirect calls in kernel

[David Woodhouse]

On Thu, 2018-01-04 at 14:00 -0600, Tom Lendacky wrote:
> Yes, lfence is sufficient. As long as the target is in the register
> before the lfence and we jump through the register all is good, i.e.:

Thanks. Can I have a Reviewed-by: for this then please:

http://git.infradead.org/users/dwmw2/linux-retpoline.git/commitdiff/08d9eda03

From: David Woodhouse <dwmw@xxxxxxxxxxxx>
Date: Thu, 4 Jan 2018 20:01:53 +0000
Subject: [PATCH] x86/retpoline: Simplify AMD variant of retpoline thunk

On AMD (which is X86_FEATURE_K8), just the lfence is sufficient.

Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
---
Âarch/x86/lib/retpoline.S | 2 +-
Â1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
index bbdda5cc136e..26070976bff0 100644
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -11,7 +11,7 @@
Â
ÂENTRY(__x86.indirect_thunk.\reg)
Â	CFI_STARTPROC
-	ALTERNATIVE "call 2f", __stringify(jmp *%\reg), X86_BUG_NO_RETPOLINE
+	ALTERNATIVE_2 "call 2f", __stringify(lfence;jmp *%\reg), X86_FEATURE_K8, __stringify(jmp *%\reg), X86_BUG_NO_RETPOLINE
Â1:
Â	lfence
Â	jmp	1b
--Â
2.14.3

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