linux-kernel - Re: [PATCH v2] x86/umip: Add emulation/spoofing for SLDT and STR instructions

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Date:   Mon, 8 Jun 2020 14:53:15 -0700
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     Brendan Shanks <bshanks@...eweavers.com>
Cc:     linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, hpa@...or.com, x86@...nel.org, ebiederm@...ssion.com,
        andi@...much.email, Babu.Moger@....com
Subject: Re: [PATCH v2] x86/umip: Add emulation/spoofing for SLDT and STR
 instructions

On Mon, Jun 08, 2020 at 11:14:54AM -0700, Brendan Shanks wrote:
> Add emulation/spoofing of SLDT and STR for both 32- and 64-bit
> processes.
> 
> Wine users have found a small number of Windows apps using SLDT that
> were crashing when run on UMIP-enabled systems.
> 
> Reported-by: Andreas Rammhold <andi@...much.email>
> Originally-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
> Signed-off-by: Brendan Shanks <bshanks@...eweavers.com>
> ---
> 
> v2: Return (GDT_ENTRY_LDT * 8) for SLDT when an LDT is set.
> 
>  arch/x86/kernel/umip.c | 34 +++++++++++++++++++++++++---------
>  1 file changed, 25 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/kernel/umip.c b/arch/x86/kernel/umip.c
> index 8d5cbe1bbb3b..a85f0b0ec2b9 100644
> --- a/arch/x86/kernel/umip.c
> +++ b/arch/x86/kernel/umip.c
> @@ -64,6 +64,8 @@
>  #define UMIP_DUMMY_GDT_BASE 0xfffffffffffe0000ULL
>  #define UMIP_DUMMY_IDT_BASE 0xffffffffffff0000ULL
>  
> +#define UMIP_DUMMY_TASK_REGISTER_SELECTOR 0x40

One more thing. How was this value selected? Would it be possible to use
GDT_ENTRY_TSS*8? Linux already uses this value.

Thanks and BR,
Ricardo