linux-kernel - [PATCH] x86/vsyscall: Do not require X86_PF

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: Windows password security audit tool. GUI, reports in PDF.

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

Message-ID: <20250625125112.3943745-3-kirill.shutemov@linux.intel.com>
Date: Wed, 25 Jun 2025 15:50:54 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: 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,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCH] x86/vsyscall: Do not require X86_PF_INSTR to emulate vsyscall

emulate_vsyscall() expects to see X86_PF_INSTR in PFEC on a vsyscall
page fault, but the CPU does not report X86_PF_INSTR if neither
X86_FEATURE_NX nor X86_FEATURE_SMEP are enabled.

X86_FEATURE_NX should be enabled on nearly all 64-bit CPUs, except for
early P4 processors that did not support this feature.

Instead of explicitly checking for X86_PF_INSTR, compare the fault
address to RIP.

On machines with X86_FEATURE_NX enabled, issue a warning if RIP is equal
to fault address but X86_PF_INSTR is absent.

Originally-by: Dave Hansen <dave.hansen@...el.com>
Link: https://lore.kernel.org/all/bd81a98b-f8d4-4304-ac55-d4151a1a77ab@intel.com
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Reported-by: Andrew Cooper <andrew.cooper3@...rix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@...rix.com>
---
 arch/x86/entry/vsyscall/vsyscall_64.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c
index c9103a6fa06e..0b0e0283994f 100644
--- a/arch/x86/entry/vsyscall/vsyscall_64.c
+++ b/arch/x86/entry/vsyscall/vsyscall_64.c
@@ -124,7 +124,8 @@ bool emulate_vsyscall(unsigned long error_code,
 	if ((error_code & (X86_PF_WRITE | X86_PF_USER)) != X86_PF_USER)
 		return false;
 
-	if (!(error_code & X86_PF_INSTR)) {
+	/* Avoid emulation unless userspace was executing from vsyscall page: */
+	if (address != regs->ip) {
 		/* Failed vsyscall read */
 		if (vsyscall_mode == EMULATE)
 			return false;
@@ -136,13 +137,16 @@ bool emulate_vsyscall(unsigned long error_code,
 		return false;
 	}
 
+
+	/* X86_PF_INSTR is only set when NX is supported: */
+	if (cpu_feature_enabled(X86_FEATURE_NX))
+		WARN_ON_ONCE(!(error_code & X86_PF_INSTR));
+
 	/*
 	 * No point in checking CS -- the only way to get here is a user mode
 	 * trap to a high address, which means that we're in 64-bit user code.
 	 */
 
-	WARN_ON_ONCE(address != regs->ip);
-
 	if (vsyscall_mode == NONE) {
 		warn_bad_vsyscall(KERN_INFO, regs,
 				  "vsyscall attempted with vsyscall=none");
-- 
2.47.2