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

[Dave Hansen]

On 6/20/25 06:53, Kirill A. Shutemov wrote:
> +bool emulate_vsyscall_pf(unsigned long error_code, struct pt_regs *regs,
> +			 unsigned long address)
> +{
> +	/* Write faults or kernel-privilege faults never get fixed up. */
> +	if ((error_code & (X86_PF_WRITE | X86_PF_USER)) != X86_PF_USER)
> +		return false;
> +
> +	if (!(error_code & X86_PF_INSTR)) {
> +		/* Failed vsyscall read */
> +		if (vsyscall_mode == EMULATE)
> +			return false;
> +
> +		/*
> +		 * User code tried and failed to read the vsyscall page.
> +		 */
> +		warn_bad_vsyscall(KERN_INFO, regs,
> +				  "vsyscall read attempt denied -- look up the vsyscall kernel parameter if you need a workaround");
> +		return false;
> +	}
> +
> +	return __emulate_vsyscall(regs, address);
> +}

For this patch that just moves the code:

Acked-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>

But, the resulting code is wonky. It needs to do something more like this:

	if ((error_code & (X86_PF_WRITE | X86_PF_USER)) != X86_PF_USER)
		return false;

	if (error_code & X86_PF_INSTR))
		return __emulate_vsyscall(regs, address);

	/* Failed vsyscall read */
	if (vsyscall_mode == EMULATE)
		return false;

	/*
	 * User code tried and failed to read the vsyscall page.
	 */
	warn_bad_vsyscall(KERN_INFO, regs, ...
	return false;

That's much more linear to read.