x86/CPU/AMD: Clear RDRAND CPUID bit on AMD family 15h/16h

There have been reports of RDRAND issues after resuming from suspend on
some AMD family 15h and family 16h systems. This issue stems from a BIOS
not performing the proper steps during resume to ensure RDRAND continues
to function properly.

RDRAND support is indicated by CPUID Fn00000001_ECX[30]. This bit can be
reset by clearing MSR C001_1004[62]. Any software that checks for RDRAND
support using CPUID, including the kernel, will believe that RDRAND is
not supported.

Update the CPU initialization to clear the RDRAND CPUID bit for any family
15h and 16h processor that supports RDRAND. If it is known that the family
15h or family 16h system does not have an RDRAND resume issue or that the
system will not be placed in suspend, the "rdrand=force" kernel parameter
can be used to stop the clearing of the RDRAND CPUID bit.

Additionally, update the suspend and resume path to save and restore the
MSR C001_1004 value to ensure that the RDRAND CPUID setting remains in
place after resuming from suspend.

Note, that clearing the RDRAND CPUID bit does not prevent a processor
that normally supports the RDRAND instruction from executing it. So any
code that determined the support based on family and model won't #UD.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chen Yu <yu.c.chen@intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: "linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>
Cc: "linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>
Cc: Nathan Chancellor <natechancellor@gmail.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: <stable@vger.kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "x86@kernel.org" <x86@kernel.org>
Link: https://lkml.kernel.org/r/7543af91666f491547bd86cebb1e17c66824ab9f.1566229943.git.thomas.lendacky@amd.com

1 files changed, 7 insertions, 0 deletions

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 47d981a86e2f..4c1971960afa 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4090,6 +4090,13 @@
 			Run specified binary instead of /init from the ramdisk,
 			used for early userspace startup. See initrd.
 
+	rdrand=		[X86]
+			force - Override the decision by the kernel to hide the
+				advertisement of RDRAND support (this affects
+				certain AMD processors because of buggy BIOS
+				support, specifically around the suspend/resume
+				path).
+
 	rdt=		[HW,X86,RDT]
 			Turn on/off individual RDT features. List is:
 			cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,