[PATCH 6.6 388/396] x86/bugs: Use fixed addressing for VERW operand

Greg Kroah-Hartman
2024-04-01T16:55:48Z

From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>

commit 8009479ee919b9a91674f48050ccbff64eafedaa upstream.

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@suse.com>
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/all/20240226-verw-arg-fix-v1-1-7b37ee6fd57d%40linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/include/asm/nospec-branch.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -337,7 +337,7 @@
* 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__ */