linux-kernel - Re: [tip: x86/urgent] x86/entry, selftests: Further improve user entry sanity checks

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: <20200820102344.GP2674@hirez.programming.kicks-ass.net>
Date:   Thu, 20 Aug 2020 12:23:44 +0200
From:   peterz@...radead.org
To:     linux-kernel@...r.kernel.org
Cc:     linux-tip-commits@...r.kernel.org,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>, x86 <x86@...nel.org>
Subject: Re: [tip: x86/urgent] x86/entry, selftests: Further improve user
 entry sanity checks

On Sat, Jul 04, 2020 at 05:49:10PM -0000, tip-bot2 for Andy Lutomirski wrote:

> diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
> index f392a8b..e83b3f1 100644
> --- a/arch/x86/entry/common.c
> +++ b/arch/x86/entry/common.c
> @@ -49,6 +49,23 @@
>  static void check_user_regs(struct pt_regs *regs)
>  {
>  	if (IS_ENABLED(CONFIG_DEBUG_ENTRY)) {
> +		/*
> +		 * Make sure that the entry code gave us a sensible EFLAGS
> +		 * register.  Native because we want to check the actual CPU
> +		 * state, not the interrupt state as imagined by Xen.
> +		 */
> +		unsigned long flags = native_save_fl();
> +		WARN_ON_ONCE(flags & (X86_EFLAGS_AC | X86_EFLAGS_DF |
> +				      X86_EFLAGS_NT));

This triggers with AC|TF on my !SMAP enabled machine.

something like so then?

diff --git a/arch/x86/include/asm/entry-common.h b/arch/x86/include/asm/entry-common.h
index a8f9315b9eae..76410964585f 100644
--- a/arch/x86/include/asm/entry-common.h
+++ b/arch/x86/include/asm/entry-common.h
@@ -18,8 +18,15 @@ static __always_inline void arch_check_user_regs(struct pt_regs *regs)
 		 * state, not the interrupt state as imagined by Xen.
 		 */
 		unsigned long flags = native_save_fl();
-		WARN_ON_ONCE(flags & (X86_EFLAGS_AC | X86_EFLAGS_DF |
-				      X86_EFLAGS_NT));
+		unsigned long mask = X86_EFLAGS_DF | X86_EFLAGS_NT;
+
+		/*
+		 * For !SMAP hardware we patch out CLAC on entry.
+		 */
+		if (boot_cpu_has(X86_FEATURE_SMAP))
+			mask |= X86_EFLAGS_AC;
+
+		WARN_ON_ONCE(flags & mask);
 
 		/* We think we came from user mode. Make sure pt_regs agrees. */
 		WARN_ON_ONCE(!user_mode(regs));