Re: [GIT pull] x86/urgent for 5.3-rc5

[Borislav Petkov <bp@suse.de>]

On Sun, Aug 25, 2019 at 10:17:23PM +0200, Borislav Petkov wrote:
> > I think WARN_ONCE() is good. It's big enough that it will show up in
> > dmesg if anybody looks, and if nobody looks I think distros still have
> > logging for things like that, don't they?
> 
> Probably. Lemme research that.

So there's a whole bunch of daemons doing desktop notifications along with a
desktop notifications spec, yadda yadda:

https://wiki.archlinux.org/index.php/Desktop_notifications

but installing an openSUSE Leap 15.1 in a guest and that is a default
desktop installation doesn't give me any notifications. I installed
notification-daemon and whatnot but nada.

Which means, that we cannot guarantee that every user would see it.
There might be installations which miss it.

So the only thing I can think of right now is to make that single line
pr_emerg() so that it atleast spews into the terminals when suspending:

linux-6qfo:~ # echo "suspend" > /sys/power/disk
linux-6qfo:~ # echo "mem" > /sys/power/state

<--- resume guest.

Message from syslogd@linux-6qfo at Aug 26 14:48:05 ...
 kernel:[   40.416145] RDRAND gives funky smelling output, might consider not using it by booting with "nordrand"

Message from syslogd@linux-6qfo at Aug 26 14:48:05 ...
 kernel:[   40.423091] RDRAND gives funky smelling output, might consider not using it by booting with "nordrand"

Message from syslogd@linux-6qfo at Aug 26 14:48:05 ...
 kernel:[   40.427426] RDRAND gives funky smelling output, might consider not using it by booting with "nordrand"

Message from syslogd@linux-6qfo at Aug 26 14:48:05 ...
 kernel:[   40.434699] RDRAND gives funky smelling output, might consider not using it by booting with "nordrand"

Message from syslogd@linux-6qfo at Aug 26 14:48:05 ...
 kernel:[   40.442587] RDRAND gives funky smelling output, might consider not using it by booting with "nordrand"

Message from syslogd@linux-6qfo at Aug 26 14:48:05 ...
 kernel:[   40.449047] RDRAND gives funky smelling output, might consider not using it by booting with "nordrand"

Message from syslogd@linux-6qfo at Aug 26 14:48:05 ...
 kernel:[   40.456328] RDRAND gives funky smelling output, might consider not using it by booting with "nordrand"

Message from syslogd@linux-6qfo at Aug 26 14:48:05 ...
 kernel:[   40.462198] RDRAND gives funky smelling output, might consider not using it by booting with "nordrand"

Message from syslogd@linux-6qfo at Aug 26 14:48:05 ...
 kernel:[   40.470120] RDRAND gives funky smelling output, might consider not using it by booting with "nordrand"

Message from syslogd@linux-6qfo at Aug 26 14:48:05 ...
 kernel:[   40.477302] RDRAND gives funky smelling output, might consider not using it by booting with "nordrand"

Message from syslogd@linux-6qfo at Aug 26 14:48:05 ...
 kernel:[   40.484605] RDRAND gives funky smelling output, might consider not using it by booting with "nordrand"

Message from syslogd@linux-6qfo at Aug 26 14:48:05 ...
 kernel:[   40.490115] RDRAND gives funky smelling output, might consider not using it by booting with "nordrand"

Message from syslogd@linux-6qfo at Aug 26 14:48:05 ...
 kernel:[   40.497508] RDRAND gives funky smelling output, might consider not using it by booting with "nordrand"

Message from syslogd@linux-6qfo at Aug 26 14:48:05 ...
 kernel:[   40.505350] RDRAND gives funky smelling output, might consider not using it by booting with "nordrand"

Message from syslogd@linux-6qfo at Aug 26 14:48:05 ...
 kernel:[   40.513336] RDRAND gives funky smelling output, might consider not using it by booting with "nordrand"

---

Assuming the user has at least a single terminal open. But someone might
have a better idea.

Current diff:

---
commit d46b23c4be1b4acae7d21c97be189131e200f6d0 (HEAD -> refs/heads/rc5+1-rdrand)
Author: Borislav Petkov <bp@suse.de>
Date:   Sun Aug 25 22:50:18 2019 +0200

    WIP

    Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Borislav Petkov <bp@suse.de>

diff --git a/arch/x86/kernel/cpu/rdrand.c b/arch/x86/kernel/cpu/rdrand.c
index 5c900f9527ff..b02d1ce91081 100644
--- a/arch/x86/kernel/cpu/rdrand.c
+++ b/arch/x86/kernel/cpu/rdrand.c
@@ -29,7 +29,8 @@ __setup("nordrand", x86_rdrand_setup);
 #ifdef CONFIG_ARCH_RANDOM
 void x86_init_rdrand(struct cpuinfo_x86 *c)
 {
-	unsigned long tmp;
+	unsigned int changed = 0;
+	unsigned long tmp, prev;
 	int i;
 
 	if (!cpu_has(c, X86_FEATURE_RDRAND))
@@ -42,5 +43,27 @@ void x86_init_rdrand(struct cpuinfo_x86 *c)
 			return;
 		}
 	}
+
+	/*
+	 * Stupid sanity-check whether RDRAND does *actually* generate
+	 * some at least random-looking data.
+	 */
+	prev = tmp;
+	for (i = 0; i < SANITY_CHECK_LOOPS; i++) {
+		if (rdrand_long(&tmp)) {
+			if (prev != tmp)
+				changed++;
+
+			prev = tmp;
+		}
+	}
+
+	if (!changed) {
+		pr_emerg(
+"RDRAND gives funky smelling output, might consider not using it by booting with \"nordrand\"");
+		WARN_ON_ONCE(1);
+	}
+
+
 }
 #endif
---

-- 
Regards/Gruss,
    Boris.

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