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@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: H. Peter Anvin <hpa@xxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxx>
> Cc: Brian Gerst <brgerst@xxxxxxxxx>
> Cc: Chen Yucong <slaoub@xxxxxxxxx>
> Cc: Chris Metcalf <cmetcalf@xxxxxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Cc: Fenghua Yu <fenghua.yu@xxxxxxxxx>
> Cc: Huang Rui <ray.huang@xxxxxxx>
> Cc: Jiri Slaby <jslaby@xxxxxxx>
> Cc: Jonathan Corbet <corbet@xxxxxxx>
> Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
> Cc: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Ravi V. Shankar <ravi.v.shankar@xxxxxxxxx>
> Cc: Shuah Khan <shuah@xxxxxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: Tony Luck <tony.luck@xxxxxxxxx>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Liang Z. Li <liang.z.li@xxxxxxxxx>
> Cc: Alexandre Julliard <julliard@xxxxxxxxxx>
> Cc: Stas Sergeev <stsp@xxxxxxx>
> Cc: x86@xxxxxxxxxx
> Cc: linux-msdos@xxxxxxxxxxxxxxx
> Reviewed-by: Andy Lutomirski <luto@xxxxxxxxxx>
> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
> ---
> 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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