The following commit has been merged into the x86/cpu branch of tip: Commit-ID: b91e7089ae70d2f7c81a4456e5b78fef498663d9 Gitweb: https://git.kernel.org/tip/b91e7089ae70d2f7c81a4456e5b78fef498663d9 Author: Brendan Shanks <bsha...@codeweavers.com> AuthorDate: Fri, 10 Jul 2020 15:45:25 -07:00 Committer: Borislav Petkov <b...@suse.de> CommitterDate: Thu, 20 Aug 2020 19:10:26 +02:00
x86/umip: Add emulation/spoofing for SLDT and STR instructions 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. Originally-by: Ricardo Neri <ricardo.neri-calde...@linux.intel.com> Reported-by: Andreas Rammhold <andi@notmuch.email> Signed-off-by: Brendan Shanks <bsha...@codeweavers.com> Signed-off-by: Borislav Petkov <b...@suse.de> Acked-by: Andy Lutomirski <l...@kernel.org> Reviewed-by: Ricardo Neri <ricardo.neri-calde...@linux.intel.com> Tested-by: Ricardo Neri <ricardo.neri-calde...@linux.intel.com> Link: https://lkml.kernel.org/r/20200710224525.21966-1-bsha...@codeweavers.com --- arch/x86/kernel/umip.c | 40 +++++++++++++++++++++++++++------------- 1 file changed, 27 insertions(+), 13 deletions(-) diff --git a/arch/x86/kernel/umip.c b/arch/x86/kernel/umip.c index 8d5cbe1..2c304fd 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 + * 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,
