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: <20210301161102.262377581@linuxfoundation.org>
Date:   Mon,  1 Mar 2021 17:13:48 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, "David P. Reed" <dpreed@...pplum.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 5.4 284/340] x86/virt: Eat faults on VMXOFF in reboot flows

From: Sean Christopherson <seanjc@...gle.com>

commit aec511ad153556640fb1de38bfe00c69464f997f upstream.

Silently ignore all faults on VMXOFF in the reboot flows as such faults
are all but guaranteed to be due to the CPU not being in VMX root.
Because (a) VMXOFF may be executed in NMI context, e.g. after VMXOFF but
before CR4.VMXE is cleared, (b) there's no way to query the CPU's VMX
state without faulting, and (c) the whole point is to get out of VMX
root, eating faults is the simplest way to achieve the desired behaior.

Technically, VMXOFF can fault (or fail) for other reasons, but all other
fault and failure scenarios are mode related, i.e. the kernel would have
to magically end up in RM, V86, compat mode, at CPL>0, or running with
the SMI Transfer Monitor active.  The kernel is beyond hosed if any of
those scenarios are encountered; trying to do something fancy in the
error path to handle them cleanly is pointless.

Fixes: 1e9931146c74 ("x86: asm/virtext.h: add cpu_vmxoff() inline function")
Reported-by: David P. Reed <dpreed@...pplum.com>
Cc: stable@...r.kernel.org
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Message-Id: <20201231002702.2223707-2-seanjc@...gle.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/include/asm/virtext.h |   17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

--- a/arch/x86/include/asm/virtext.h
+++ b/arch/x86/include/asm/virtext.h
@@ -30,15 +30,22 @@ static inline int cpu_has_vmx(void)
 }
 
 
-/** Disable VMX on the current CPU
+/**
+ * cpu_vmxoff() - Disable VMX on the current CPU
  *
- * vmxoff causes a undefined-opcode exception if vmxon was not run
- * on the CPU previously. Only call this function if you know VMX
- * is enabled.
+ * Disable VMX and clear CR4.VMXE (even if VMXOFF faults)
+ *
+ * Note, VMXOFF causes a #UD if the CPU is !post-VMXON, but it's impossible to
+ * atomically track post-VMXON state, e.g. this may be called in NMI context.
+ * Eat all faults as all other faults on VMXOFF faults are mode related, i.e.
+ * faults are guaranteed to be due to the !post-VMXON check unless the CPU is
+ * magically in RM, VM86, compat mode, or at CPL>0.
  */
 static inline void cpu_vmxoff(void)
 {
-	asm volatile ("vmxoff");
+	asm_volatile_goto("1: vmxoff\n\t"
+			  _ASM_EXTABLE(1b, %l[fault]) :::: fault);
+fault:
 	cr4_clear_bits(X86_CR4_VMXE);
 }
 


Powered by blists - more mailing lists

Powered by Openwall GNU/*/Linux Powered by OpenVZ