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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <9d351d80-66fe-486f-bdb3-370859dc47cc@intel.com>
Date: Fri, 20 Jun 2025 11:43:25 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
 Andy Lutomirski <luto@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
 Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
 Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
 "H. Peter Anvin" <hpa@...or.com>, Peter Zijlstra <peterz@...radead.org>,
 Ard Biesheuvel <ardb@...nel.org>, "Paul E. McKenney" <paulmck@...nel.org>,
 Josh Poimboeuf <jpoimboe@...nel.org>,
 Xiongwei Song <xiongwei.song@...driver.com>, Xin Li <xin3.li@...el.com>,
 "Mike Rapoport (IBM)" <rppt@...nel.org>,
 Brijesh Singh <brijesh.singh@....com>, Michael Roth <michael.roth@....com>,
 Tony Luck <tony.luck@...el.com>, Alexey Kardashevskiy <aik@....com>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Jonathan Corbet <corbet@....net>, Sohil Mehta <sohil.mehta@...el.com>,
 Ingo Molnar <mingo@...nel.org>,
 Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
 Daniel Sneddon <daniel.sneddon@...ux.intel.com>,
 Kai Huang <kai.huang@...el.com>, Sandipan Das <sandipan.das@....com>,
 Breno Leitao <leitao@...ian.org>, Rick Edgecombe
 <rick.p.edgecombe@...el.com>, Alexei Starovoitov <ast@...nel.org>,
 Hou Tao <houtao1@...wei.com>, Juergen Gross <jgross@...e.com>,
 Vegard Nossum <vegard.nossum@...cle.com>, Kees Cook <kees@...nel.org>,
 Eric Biggers <ebiggers@...gle.com>, Jason Gunthorpe <jgg@...pe.ca>,
 "Masami Hiramatsu (Google)" <mhiramat@...nel.org>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Luis Chamberlain <mcgrof@...nel.org>, Yuntao Wang <ytcoode@...il.com>,
 Rasmus Villemoes <linux@...musvillemoes.dk>,
 Christophe Leroy <christophe.leroy@...roup.eu>, Tejun Heo <tj@...nel.org>,
 Changbin Du <changbin.du@...wei.com>,
 Huang Shijie <shijie@...amperecomputing.com>,
 Geert Uytterhoeven <geert+renesas@...der.be>,
 Namhyung Kim <namhyung@...nel.org>,
 Arnaldo Carvalho de Melo <acme@...hat.com>, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCHv6 07/16] x86/vsyscall: Reorganize the #PF emulation code

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@...ux.intel.com>

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.