From: Borislav Petkov <bp@suse.de>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Pu Wen <puwen@hygon.cn>, Thomas Gleixner <tglx@linutronix.de>,
Tom Lendacky <thomas.lendacky@amd.com>,
Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
the arch/x86 maintainers <x86@kernel.org>
Subject: Re: [GIT pull] x86/urgent for 5.3-rc5
Date: Sun, 25 Aug 2019 22:17:23 +0200 [thread overview]
Message-ID: <20190825201723.GG20639@zn.tnic> (raw)
In-Reply-To: <CAHk-=wjcUQjK=SqPGdZCDEKntOZEv34n9wKJhBrPzcL6J7nDqQ@mail.gmail.com>
On Sun, Aug 25, 2019 at 12:59:25PM -0700, Linus Torvalds 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.
> Hopefully this never actually triggers in practice, thanks to rdrand
> being turned off on known-bad machines now, and Zen 2 being fixed.
Right. Here's v2, will do a proper patch tomorrow:
---
diff --git a/arch/x86/kernel/cpu/rdrand.c b/arch/x86/kernel/cpu/rdrand.c
index 5c900f9527ff..00a9d13c0a92 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 +43,24 @@ 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)
+ WARN_ONCE(1,
+"RDRAND gives funky smelling output, might consider not using it by booting with \"nordrand\"");
+
}
#endif
--
Regards/Gruss,
Boris.
SUSE Software Solutions Germany GmbH, GF: Felix Imendörffer, HRB 247165, AG München
next prev parent reply other threads:[~2019-08-25 20:17 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-25 9:43 [GIT pull] irq/urgent for 5.3-rc5 Thomas Gleixner
2019-08-25 9:43 ` [GIT pull] x86/urgent " Thomas Gleixner
2019-08-25 17:18 ` Linus Torvalds
2019-08-25 17:30 ` Borislav Petkov
2019-08-25 17:37 ` Linus Torvalds
2019-08-25 18:29 ` Borislav Petkov
2019-08-25 18:38 ` Linus Torvalds
2019-08-25 19:32 ` Borislav Petkov
2019-08-25 19:35 ` Linus Torvalds
2019-08-25 19:49 ` Borislav Petkov
2019-08-25 19:59 ` Linus Torvalds
2019-08-25 20:17 ` Borislav Petkov [this message]
2019-08-26 12:53 ` Borislav Petkov
2019-08-27 16:55 ` Linus Torvalds
2019-08-27 17:39 ` Borislav Petkov
2019-08-27 17:46 ` Linus Torvalds
2019-08-27 17:59 ` Borislav Petkov
2019-08-28 15:20 ` David Sterba
2019-08-28 15:53 ` David Sterba
2019-10-02 19:09 ` [tip: x86/cpu] x86/rdrand: Sanity-check RDRAND output tip-bot2 for Borislav Petkov
2019-08-25 17:40 ` [GIT pull] x86/urgent for 5.3-rc5 pr-tracker-bot
2019-08-25 9:43 ` [GIT pull] timers/urgent " Thomas Gleixner
2019-08-25 17:40 ` pr-tracker-bot
2019-08-25 9:43 ` [GIT pull] perf/urgent " Thomas Gleixner
2019-08-25 17:40 ` pr-tracker-bot
2019-08-25 9:43 ` [GIT pull] sched/urgent " Thomas Gleixner
2019-08-25 17:40 ` pr-tracker-bot
2019-08-25 17:40 ` [GIT pull] irq/urgent " pr-tracker-bot
-- strict thread matches above, loose matches on Subject: below --
2019-08-18 11:34 [GIT pull] efi/urgent " Thomas Gleixner
2019-08-18 11:34 ` [GIT pull] x86/urgent " Thomas Gleixner
2019-08-18 16:55 ` pr-tracker-bot
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