Re: [tip: x86/urgent] x86/bugs: Use code segment selector for VERW operand

On Wed, Oct 09, 2024 at 08:11:02AM +0200, Borislav Petkov wrote:

On Tue, Oct 08, 2024 at 10:45:36PM -0000, tip-bot2 for Pawan Gupta wrote:

...

.macro CLEAR_CPU_BUFFERS

• ALTERNATIVE "", __stringify(verw _ASM_RIP(mds_verw_sel)), X86_FEATURE_CLEAR_CPU_BUF

+#ifdef CONFIG_X86_64

• ALTERNATIVE "", "verw mds_verw_sel(%rip)", X86_FEATURE_CLEAR_CPU_BUF

+#else

• /*

• * In 32bit mode, the memory operand must be a %cs reference. The data
  

• * segments may not be usable (vm86 mode), and the stack segment may not
  

• * be flat (ESPFIX32).
  

• */
  

• ALTERNATIVE "", "verw %cs:mds_verw_sel", X86_FEATURE_CLEAR_CPU_BUF

+#endif

So why didn't we ifdef the "verw mds_verw_sel(%rip)" and "verw %cs:mds_verw_sel" macro argument instead of adding more bigger ugly ifdeffery?

You need ifdeffery either way around, either directly like this or for that macro. This is simple and straight forward.