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

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Message-ID: <1f2b0ed7-67f6-410e-b05e-d87ba3ee396e@intel.com>
Date: Tue, 7 Oct 2025 15:52:02 -0700
From: Sohil Mehta <sohil.mehta@...el.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>, "tglx@...utronix.de"
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Subject: Re: [PATCH v10 08/15] x86/vsyscall: Reorganize the page fault
 emulation code

On 10/7/2025 12:53 PM, Edgecombe, Rick P wrote:

> But I'm looking at this applied. The following patches (which don't include that
> hunk), add another call site:
> 
> bool emulate_vsyscall_gp(struct pt_regs *regs)
> {
> 	if (!cpu_feature_enabled(X86_FEATURE_LASS))
> 		return false;
> 
> 	/* Emulate only if the RIP points to the vsyscall address */
> 	if (!is_vsyscall_vaddr(regs->ip))
> 		return false;
> 
> 	return __emulate_vsyscall(regs, regs->ip);
> }
> 
> If indeed we should add a check, it should probably go in one of the later
> patches and not this one.

We already check CS before calling emulate_vsyscall_gp().

if (user_mode(regs)) {

...
	if (emulate_vsyscall_gp(regs))
		goto exit;

...
}