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Subject[PATCH v3] x86/umip: Add emulation/spoofing for SLDT and STR instructions
Date
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@notmuch.email>
Originally-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Signed-off-by: Brendan Shanks <bshanks@codeweavers.com>
---

v3: Use (GDT_ENTRY_TSS * 8) for task register selector instead of
harcoding 0x40.

arch/x86/kernel/umip.c | 32 +++++++++++++++++++++++---------
1 file changed, 23 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/umip.c b/arch/x86/kernel/umip.c
index 8d5cbe1bbb3b..166c579b0273 100644
--- a/arch/x86/kernel/umip.c
+++ b/arch/x86/kernel/umip.c
@@ -244,16 +244,35 @@ 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(&current->mm->context.ldt_usr_sem);
+ if (current->mm->context.ldt)
+ dummy_value = GDT_ENTRY_LDT * 8;
+ else
+ dummy_value = 0;
+ up_read(&current->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
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