linux-kernel - [PATCH v9 27/29] x86/traps: Fixup general protection faults caused by UMIP

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Message-Id: <1507089272-32733-28-git-send-email-ricardo.neri-calderon@linux.intel.com>
Date:   Tue,  3 Oct 2017 20:54:30 -0700
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>, Borislav Petkov <bp@...e.de>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Brian Gerst <brgerst@...il.com>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Liang Z Li <liang.z.li@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Huang Rui <ray.huang@....com>, Jiri Slaby <jslaby@...e.cz>,
        Jonathan Corbet <corbet@....net>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Chen Yucong <slaoub@...il.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Shuah Khan <shuah@...nel.org>, linux-kernel@...r.kernel.org,
        x86@...nel.org, ricardo.neri@...el.com,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Tony Luck <tony.luck@...el.com>
Subject: [PATCH v9 27/29] x86/traps: Fixup general protection faults caused by UMIP

If the User-Mode Instruction Prevention CPU feature is available and
enabled, a general protection fault will be issued if the instructions
sgdt, sldt, sidt, str or smsw are executed from user-mode context
(CPL > 0). If the fault was caused by any of the instructions protected
by UMIP, fixup_umip_exception() will emulate dummy results for these
instructions as follows: if running a 32-bit process, sgdt, sidt and smsw
are emulated; str and sldt are not emulated. No emulation is done for
64-bit processes.

If emulation is successful, the result is passed to the user space program
and no SIGSEGV signal is emitted.

Please note that fixup_umip_exception() also caters for the case when
the fault originated while running in virtual-8086 mode.

Cc: Andy Lutomirski <luto@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Borislav Petkov <bp@...e.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Chen Yucong <slaoub@...il.com>
Cc: Chris Metcalf <cmetcalf@...lanox.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Fenghua Yu <fenghua.yu@...el.com>
Cc: Huang Rui <ray.huang@....com>
Cc: Jiri Slaby <jslaby@...e.cz>
Cc: Jonathan Corbet <corbet@....net>
Cc: Michael S. Tsirkin <mst@...hat.com>
Cc: Paul Gortmaker <paul.gortmaker@...driver.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ravi V. Shankar <ravi.v.shankar@...el.com>
Cc: Shuah Khan <shuah@...nel.org>
Cc: Vlastimil Babka <vbabka@...e.cz>
Cc: Tony Luck <tony.luck@...el.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: x86@...nel.org
Reviewed-by: Andy Lutomirski <luto@...nel.org>
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
---
 arch/x86/kernel/traps.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index a5791f3..4c0aa6c 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -60,6 +60,7 @@
 #include <asm/trace/mpx.h>
 #include <asm/mpx.h>
 #include <asm/vm86.h>
+#include <asm/umip.h>
 
 #ifdef CONFIG_X86_64
 #include <asm/x86_init.h>
@@ -514,6 +515,10 @@ do_general_protection(struct pt_regs *regs, long error_code)
 	RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
 	cond_local_irq_enable(regs);
 
+	if (static_cpu_has(X86_FEATURE_UMIP))
+		if (user_mode(regs) && fixup_umip_exception(regs))
+			return;
+
 	if (v8086_mode(regs)) {
 		local_irq_enable();
 		handle_vm86_fault((struct kernel_vm86_regs *) regs, error_code);
-- 
2.7.4