Re: [tip: x86/urgent] x86/bugs: Use code segment selector for VERW operand
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- Subject: Re: [tip: x86/urgent] x86/bugs: Use code segment selector for VERW operand
- From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
- Date: Wed, 9 Oct 2024 09:34:37 +0200
- Cc: linux-kernel@xxxxxxxxxxxxxxx, linux-tip-commits@xxxxxxxxxxxxxxx, Robert Gill <rtgill82@xxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, stable@xxxxxxxxxxxxxxx, #@tip-bot2.tec.linutronix.de, 5.10+@xxxxxxxxxxxxxxxxxxxxxxxxxx, Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>, Brian Gerst <brgerst@xxxxxxxxx>, Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>, x86@xxxxxxxxxx
- In-reply-to: <20241009061102.GBZwYediMceBEfSEFo@fat_crate.local>
- References: <172842753652.1442.15253433006014560776.tip-bot2@tip-bot2> <20241009061102.GBZwYediMceBEfSEFo@fat_crate.local>
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.
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