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 <[email protected]>
Originally-by: Ricardo Neri <[email protected]>
Signed-off-by: Brendan Shanks <[email protected]>
---
v4: Use braces for every clause of the conditional. I tried a switch(),
but it takes more lines and looks more cluttered (especially with the
#ifdef).
Also replace out-of-date comment at top of file.
arch/x86/kernel/umip.c | 38 ++++++++++++++++++++++++++------------
1 file changed, 26 insertions(+), 12 deletions(-)
diff --git a/arch/x86/kernel/umip.c b/arch/x86/kernel/umip.c
index 8d5cbe1bbb3b..62f4f0afb979 100644
--- a/arch/x86/kernel/umip.c
+++ b/arch/x86/kernel/umip.c
@@ -45,11 +45,12 @@
* value that, lies close to the top of the kernel memory. The limit for the GDT
* and the IDT are set to zero.
*
- * Given that SLDT and STR are not commonly used in programs that run on WineHQ
- * or DOSEMU2, they are not emulated.
- *
* The instruction smsw is emulated to return the value that the register CR0
* has at boot time as set in the head_32.
+ * sldt and str are emulated to return the values that the kernel programmatically
+ * assigns:
+ * - sldt returns (GDT_ENTRY_LDT * 8) if an LDT has been set, 0 if not.
+ * - str returns (GDT_ENTRY_TSS * 8).
*
* Emulation is provided for both 32-bit and 64-bit processes.
*
@@ -244,16 +245,34 @@ static int emulate_umip_insn(struct insn *insn, int umip_inst,
*data_size += UMIP_GDT_IDT_LIMIT_SIZE;
memcpy(data, &dummy_limit, UMIP_GDT_IDT_LIMIT_SIZE);
- } else if (umip_inst == UMIP_INST_SMSW) {
- unsigned long dummy_value = CR0_STATE;
+ } else if (umip_inst == UMIP_INST_SMSW || umip_inst == UMIP_INST_SLDT ||
+ umip_inst == UMIP_INST_STR) {
+ unsigned long dummy_value;
+
+ if (umip_inst == UMIP_INST_SMSW) {
+ dummy_value = CR0_STATE;
+ } else if (umip_inst == UMIP_INST_STR) {
+ dummy_value = GDT_ENTRY_TSS * 8;
+ } else if (umip_inst == UMIP_INST_SLDT) {
+#ifdef CONFIG_MODIFY_LDT_SYSCALL
+ down_read(¤t->mm->context.ldt_usr_sem);
+ if (current->mm->context.ldt)
+ dummy_value = GDT_ENTRY_LDT * 8;
+ else
+ dummy_value = 0;
+ up_read(¤t->mm->context.ldt_usr_sem);
+#else
+ dummy_value = 0;
+#endif
+ }
/*
- * Even though the CR0 register has 4 bytes, the number
+ * For these 3 instructions, the number
* of bytes to be copied in the result buffer is determined
* by whether the operand is a register or a memory location.
* If operand is a register, return as many bytes as the operand
* size. If operand is memory, return only the two least
- * siginificant bytes of CR0.
+ * siginificant bytes.
*/
if (X86_MODRM_MOD(insn->modrm.value) == 3)
*data_size = insn->opnd_bytes;
@@ -261,7 +280,6 @@ static int emulate_umip_insn(struct insn *insn, int umip_inst,
*data_size = 2;
memcpy(data, &dummy_value, *data_size);
- /* STR and SLDT are not emulated */
} else {
return -EINVAL;
}
@@ -383,10 +401,6 @@ bool fixup_umip_exception(struct pt_regs *regs)
umip_pr_warn(regs, "%s instruction cannot be used by applications.\n",
umip_insns[umip_inst]);
- /* Do not emulate (spoof) SLDT or STR. */
- if (umip_inst == UMIP_INST_STR || umip_inst == UMIP_INST_SLDT)
- return false;
-
umip_pr_warn(regs, "For now, expensive software emulation returns the result.\n");
if (emulate_umip_insn(&insn, umip_inst, dummy_data, &dummy_data_size,
--
2.26.2
On Tue, Jun 09, 2020 at 10:54:23AM -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 <[email protected]>
> Originally-by: Ricardo Neri <[email protected]>
> Signed-off-by: Brendan Shanks <[email protected]>
> ---
>
> v4: Use braces for every clause of the conditional. I tried a switch(),
> but it takes more lines and looks more cluttered (especially with the
> #ifdef).
> Also replace out-of-date comment at top of file.
>
> arch/x86/kernel/umip.c | 38 ++++++++++++++++++++++++++------------
> 1 file changed, 26 insertions(+), 12 deletions(-)
>
> diff --git a/arch/x86/kernel/umip.c b/arch/x86/kernel/umip.c
> index 8d5cbe1bbb3b..62f4f0afb979 100644
> --- a/arch/x86/kernel/umip.c
> +++ b/arch/x86/kernel/umip.c
> @@ -45,11 +45,12 @@
> * value that, lies close to the top of the kernel memory. The limit for the GDT
> * and the IDT are set to zero.
> *
> - * Given that SLDT and STR are not commonly used in programs that run on WineHQ
> - * or DOSEMU2, they are not emulated.
> - *
> * The instruction smsw is emulated to return the value that the register CR0
> * has at boot time as set in the head_32.
> + * sldt and str are emulated to return the values that the kernel programmatically
> + * assigns:
> + * - sldt returns (GDT_ENTRY_LDT * 8) if an LDT has been set, 0 if not.
> + * - str returns (GDT_ENTRY_TSS * 8).
Probably for consistency with the rest of the document the instruction
names should be capitalized (I know that smsw was not capitalized before
:/). Maybe maintainers can fix this when applying?
Other than that, FWIW:
Reviewed-by: Ricardo Neri <[email protected]>
Tested-by: Ricardo Neri <[email protected]>
On 10:54 09.06.20, 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 <[email protected]>
> Originally-by: Ricardo Neri <[email protected]>
> Signed-off-by: Brendan Shanks <[email protected]>
> ---
>
> v4: Use braces for every clause of the conditional. I tried a switch(),
> but it takes more lines and looks more cluttered (especially with the
> #ifdef).
> Also replace out-of-date comment at top of file.
>
> arch/x86/kernel/umip.c | 38 ++++++++++++++++++++++++++------------
> 1 file changed, 26 insertions(+), 12 deletions(-)
>
> diff --git a/arch/x86/kernel/umip.c b/arch/x86/kernel/umip.c
> index 8d5cbe1bbb3b..62f4f0afb979 100644
> --- a/arch/x86/kernel/umip.c
> +++ b/arch/x86/kernel/umip.c
> @@ -45,11 +45,12 @@
> * value that, lies close to the top of the kernel memory. The limit for the GDT
> * and the IDT are set to zero.
> *
> - * Given that SLDT and STR are not commonly used in programs that run on WineHQ
> - * or DOSEMU2, they are not emulated.
> - *
> * The instruction smsw is emulated to return the value that the register CR0
> * has at boot time as set in the head_32.
> + * sldt and str are emulated to return the values that the kernel programmatically
> + * assigns:
> + * - sldt returns (GDT_ENTRY_LDT * 8) if an LDT has been set, 0 if not.
> + * - str returns (GDT_ENTRY_TSS * 8).
> *
> * Emulation is provided for both 32-bit and 64-bit processes.
> *
> @@ -244,16 +245,34 @@ static int emulate_umip_insn(struct insn *insn, int umip_inst,
> *data_size += UMIP_GDT_IDT_LIMIT_SIZE;
> memcpy(data, &dummy_limit, UMIP_GDT_IDT_LIMIT_SIZE);
>
> - } else if (umip_inst == UMIP_INST_SMSW) {
> - unsigned long dummy_value = CR0_STATE;
> + } else if (umip_inst == UMIP_INST_SMSW || umip_inst == UMIP_INST_SLDT ||
> + umip_inst == UMIP_INST_STR) {
> + unsigned long dummy_value;
> +
> + if (umip_inst == UMIP_INST_SMSW) {
> + dummy_value = CR0_STATE;
> + } else if (umip_inst == UMIP_INST_STR) {
> + dummy_value = GDT_ENTRY_TSS * 8;
> + } else if (umip_inst == UMIP_INST_SLDT) {
> +#ifdef CONFIG_MODIFY_LDT_SYSCALL
> + down_read(¤t->mm->context.ldt_usr_sem);
> + if (current->mm->context.ldt)
> + dummy_value = GDT_ENTRY_LDT * 8;
> + else
> + dummy_value = 0;
> + up_read(¤t->mm->context.ldt_usr_sem);
> +#else
> + dummy_value = 0;
> +#endif
> + }
>
> /*
> - * Even though the CR0 register has 4 bytes, the number
> + * For these 3 instructions, the number
> * of bytes to be copied in the result buffer is determined
> * by whether the operand is a register or a memory location.
> * If operand is a register, return as many bytes as the operand
> * size. If operand is memory, return only the two least
> - * siginificant bytes of CR0.
> + * siginificant bytes.
> */
> if (X86_MODRM_MOD(insn->modrm.value) == 3)
> *data_size = insn->opnd_bytes;
> @@ -261,7 +280,6 @@ static int emulate_umip_insn(struct insn *insn, int umip_inst,
> *data_size = 2;
>
> memcpy(data, &dummy_value, *data_size);
> - /* STR and SLDT are not emulated */
> } else {
> return -EINVAL;
> }
> @@ -383,10 +401,6 @@ bool fixup_umip_exception(struct pt_regs *regs)
> umip_pr_warn(regs, "%s instruction cannot be used by applications.\n",
> umip_insns[umip_inst]);
>
> - /* Do not emulate (spoof) SLDT or STR. */
> - if (umip_inst == UMIP_INST_STR || umip_inst == UMIP_INST_SLDT)
> - return false;
> -
> umip_pr_warn(regs, "For now, expensive software emulation returns the result.\n");
>
> if (emulate_umip_insn(&insn, umip_inst, dummy_data, &dummy_data_size,
> --
> 2.26.2
>
A bit late but I was able to test my workload with the above patch
applied on 5.7.2.
Tested-by: Andreas Rammhold <[email protected]>