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x86/bugs: Use fixed addressing for VERW operand

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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>
This commit is contained in:
Pawan Gupta 2024-02-26 15:52:33 -08:00 committed by Greg Kroah-Hartman
parent a492d6dad9
commit 367b4ce0d7
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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@ -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__ */