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

Ricardo Neri
2017-10-04T03:56:22Z

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@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Chen Yucong <slaoub@gmail.com>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Huang Rui <ray.huang@amd.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi V. Shankar <ravi.v.shankar@intel.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: x86@kernel.org
Reviewed-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.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