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x86/bugs: Use fixed addressing for VERW operand

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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
This commit is contained in:
Pawan Gupta 2024-02-26 15:52:33 -08:00 committed by Dave Hansen
parent 6890cb1ace
commit 8009479ee9
1 changed files with 1 additions and 1 deletions
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2
arch/x86/include/asm/nospec-branch.h
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@ -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__ */