linux-kernel - [tip: x86/urgent] x86/bugs: Use fixed addressing for VERW operand

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Date: Tue, 27 Feb 2024 01:19:05 -0000
From: "tip-bot2 for Pawan Gupta" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Nikolay Borisov <nik.borisov@...e.com>,
 Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
 Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: x86/urgent] x86/bugs: Use fixed addressing for VERW operand

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     8009479ee919b9a91674f48050ccbff64eafedaa
Gitweb:        https://git.kernel.org/tip/8009479ee919b9a91674f48050ccbff64eafedaa
Author:        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
AuthorDate:    Mon, 26 Feb 2024 15:52:33 -08:00
Committer:     Dave Hansen <dave.hansen@...ux.intel.com>
CommitterDate: Mon, 26 Feb 2024 17:06:17 -08:00

x86/bugs: Use fixed addressing for VERW operand

The macro used for MDS mitigation executes VERW with relative
addressing for the operand. This was necessary in earlier versions of
the series. Now it is unnecessary and creates a problem for backports
on older kernels that don't support relocations in alternatives.
Relocation support was added by commit 270a69c4485d ("x86/alternative:
Support relocations in alternatives").  Also asm for fixed addressing
is much cleaner than relative RIP addressing.

Simplify the asm by using fixed addressing for VERW operand.

[ dhansen: tweak changelog ]

Closes: https://lore.kernel.org/lkml/20558f89-299b-472e-9a96-171403a83bd6@suse.com/
Fixes: baf8361e5455 ("x86/bugs: Add asm helpers for executing VERW")
Reported-by: Nikolay Borisov <nik.borisov@...e.com>
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Link: https://lore.kernel.org/all/20240226-verw-arg-fix-v1-1-7b37ee6fd57d%40linux.intel.com
---
 arch/x86/include/asm/nospec-branch.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 2aa52ca..ab19c7f 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -323,7 +323,7 @@
  * Note: Only the memory operand variant of VERW clears the CPU buffers.
  */
 .macro CLEAR_CPU_BUFFERS
-	ALTERNATIVE "", __stringify(verw _ASM_RIP(mds_verw_sel)), X86_FEATURE_CLEAR_CPU_BUF
+	ALTERNATIVE "", __stringify(verw mds_verw_sel), X86_FEATURE_CLEAR_CPU_BUF
 .endm
 
 #else /* __ASSEMBLY__ */