Re: [PATCH v7 23/26] x86/traps: Fixup general protection faults caused by UMIP

Borislav Petkov
2017-06-09T13:02:48Z

On Fri, May 05, 2017 at 11:17:21AM -0700, Ricardo Neri 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_exception will emulate dummy results for these

Please end function names with parentheses.

> instructions. 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: Liang Z. Li <liang.z.li@intel.com>
> Cc: Alexandre Julliard <julliard@winehq.org>
> Cc: Stas Sergeev <stsp@list.ru>
> Cc: x86@kernel.org
> Cc: linux-msdos@vger.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 | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> index 3995d3a..cec548d 100644
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -65,6 +65,7 @@
> #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>
> @@ -526,6 +527,9 @@ 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);
>

Almost definitely:

if (static_cpu_has(X86_FEATURE_UMIP)) {
if (...

> + if (user_mode(regs) && fixup_umip_exception(regs))
> + return;

We don't want to punish !UMIP machines.

--
Regards/Gruss,
Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
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