linux-kernel - Re: [PATCHv6 07/16] x86/vsyscall: Reorganize the #PF emulation code

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Message-ID: <hhbqjpkpdi5oe77lfosjpgyvvhvxgwolb45ll5rmwbzsdt27h5@hgv57r543ryl>
Date: Tue, 24 Jun 2025 14:37:21 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Dave Hansen <dave.hansen@...el.com>
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Subject: Re: [PATCHv6 07/16] x86/vsyscall: Reorganize the #PF emulation code

On Mon, Jun 23, 2025 at 08:32:53AM -0700, Dave Hansen wrote:
> On 6/23/25 05:41, Kirill A. Shutemov wrote:
> > So, IIUC, that's dependency of vsyscall PF on NX. Do we want to disable
> > vsyscall on boot if NX is not available?
> 
> Well, vsyscall=none can break old userspace, so forcing it on old
> hardware doesn't seem like a great idea.
> 
> But, either way, this doesn't really appear to be a LASS issue. This code:
> 
> >         if (!(error_code & X86_PF_INSTR)) {
> >                 /* Failed vsyscall read */
> >                 if (vsyscall_mode == EMULATE)
> >                         return false;
> 
> Is really asking the question:
> 
> 	Is this #PF from an instruction fetch in the vsyscall page?
> 
> That _should_ be able to be done by comparing CR2 and regs->rip. In
> fact, that's done just below anyway:
> 
> 	WARN_ON_ONCE(address != regs->ip);
> 
> So I think we can fix this up with something like the attached patch
> which just drives the if() from regs->rip and make the warning NX-only.

Looks good to me.

Do you want me to include it into this patchset or will you apply it
separately?

-- 
  Kiryl Shutsemau / Kirill A. Shutemov