On Fri, 2016-12-23 at 18:11 -0800, Andy Lutomirski wrote:
On Fri, Dec 23, 2016 at 5:37 PM, Ricardo Neri <ricardo.neri-calderon(a)linux.intel.com> wrote:
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_exceptino will emulate dummy results for these instructions.
Cc: Andy Lutomirski <luto(a)kernel.org> Cc: Andrew Morton <akpm(a)linux-foundation.org> Cc: H. Peter Anvin <hpa(a)zytor.com> Cc: Borislav Petkov <bp(a)suse.de> Cc: Brian Gerst <brgerst(a)gmail.com> Cc: Chen Yucong <slaoub(a)gmail.com> Cc: Chris Metcalf <cmetcalf(a)mellanox.com> Cc: Dave Hansen <dave.hansen(a)linux.intel.com> Cc: Fenghua Yu <fenghua.yu(a)intel.com> Cc: Huang Rui <ray.huang(a)amd.com> Cc: Jiri Slaby <jslaby(a)suse.cz> Cc: Jonathan Corbet <corbet(a)lwn.net> Cc: Michael S. Tsirkin <mst(a)redhat.com> Cc: Paul Gortmaker <paul.gortmaker(a)windriver.com> Cc: Peter Zijlstra <peterz(a)infradead.org> Cc: Ravi V. Shankar <ravi.v.shankar(a)intel.com> Cc: Shuah Khan <shuah(a)kernel.org> Cc: Vlastimil Babka <vbabka(a)suse.cz> Cc: Tony Luck <tony.luck(a)intel.com> Cc: Paolo Bonzini <pbonzini(a)redhat.com> Cc: Liang Z. Li <liang.z.li(a)intel.com> Cc: Alexandre Julliard <julliard(a)winehq.org> Cc: Stas Sergeev <stsp(a)list.ru> Cc: x86(a)kernel.org Cc: linux-msdos(a)vger.kernel.org Signed-off-by: Ricardo Neri <ricardo.neri-calderon(a)linux.intel.com> --- arch/x86/kernel/traps.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index bf0c6d0..5044fb3 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -64,6 +64,7 @@ #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> @@ -491,6 +492,9 @@ 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 (user_mode(regs) && !fixup_umip_exception(regs)) + return; +
I would do fixup_umip_exception(regs) == 0 to make it more obvious what's going on.
Sure. I will make this change.
Also, since you're allowing this in v8086 mode, I think this should have an explicit test in tools/testing/selftests/x86/entry_from_vm86.c. I *think* it will work fine, but the pt_regs handling in vm86 mode is quite scary and has been rewritten recently.
I will include a test for this. Thanks and BR, Ricardo