linux-kernel - Re: [PATCH v10 08/15] x86/vsyscall: Reorganize the page fault emulation code

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Message-ID: <e3c7987f-7f8d-41bb-9d4d-966f35941757@intel.com>
Date: Thu, 30 Oct 2025 12:28:52 -0700
From: Sohil Mehta <sohil.mehta@...el.com>
To: Andy Lutomirski <luto@...nel.org>, Dave Hansen <dave.hansen@...el.com>,
	Rick P Edgecombe <rick.p.edgecombe@...el.com>, Thomas Gleixner
	<tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov
	<bp@...en8.de>, the arch/x86 maintainers <x86@...nel.org>, Dave Hansen
	<dave.hansen@...ux.intel.com>
CC: Jonathan Corbet <corbet@....net>, Ard Biesheuvel <ardb@...nel.org>,
	"david.laight.linux@...il.com" <david.laight.linux@...il.com>,
	"jpoimboe@...nel.org" <jpoimboe@...nel.org>, Andrew Cooper
	<andrew.cooper3@...rix.com>, Tony Luck <tony.luck@...el.com>, "Alexander
 Shishkin" <alexander.shishkin@...ux.intel.com>, "Kirill A . Shutemov"
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	<linux-doc@...r.kernel.org>, Kees Cook <kees@...nel.org>, "H. Peter Anvin"
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	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>, Geert Uytterhoeven
	<geert@...ux-m68k.org>
Subject: Re: [PATCH v10 08/15] x86/vsyscall: Reorganize the page fault
 emulation code

Thank you for taking a look at these patches.

On 10/30/2025 9:58 AM, Andy Lutomirski wrote:

> So I think all that's needed is to update "[PATCH v10 10/15] x86/vsyscall: Add vsyscall emulation for #GP" to check user_64bit_mode(regs) for the vsyscall case.  (As submitted, unless I missed something while composing the patches in my head, it's only checking user_mode(regs), and I think it's worth the single extra line of code to make the result a tiny bit more robust.)

I probably don't understand all the nuances here. But, the goal of the
check seems to ensure a 32-bit process running on a 64-bit kernel
doesn't ever go through this vsyscall emulation code, right?

I guess a user_64bit_mode(regs) check wouldn't harm. I'll add it when
the vsyscall series is posted.