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-rw-r--r--arch/x86/kernel/umip.c185
1 files changed, 92 insertions, 93 deletions
diff --git a/arch/x86/kernel/umip.c b/arch/x86/kernel/umip.c
index f8f3cfda01ae..d432f3824f0c 100644
--- a/arch/x86/kernel/umip.c
+++ b/arch/x86/kernel/umip.c
@@ -1,6 +1,6 @@
/*
- * umip.c Emulation for instruction protected by the Intel User-Mode
- * Instruction Prevention feature
+ * umip.c Emulation for instruction protected by the User-Mode Instruction
+ * Prevention feature
*
* Copyright (c) 2017, Intel Corporation.
* Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
@@ -18,10 +18,10 @@
/** DOC: Emulation for User-Mode Instruction Prevention (UMIP)
*
- * The feature User-Mode Instruction Prevention present in recent Intel
- * processor prevents a group of instructions (sgdt, sidt, sldt, smsw, and str)
- * from being executed with CPL > 0. Otherwise, a general protection fault is
- * issued.
+ * User-Mode Instruction Prevention is a security feature present in recent
+ * x86 processors that, when enabled, prevents a group of instructions (SGDT,
+ * SIDT, SLDT, SMSW and STR) from being run in user mode by issuing a general
+ * protection fault if the instruction is executed with CPL > 0.
*
* Rather than relaying to the user space the general protection fault caused by
* the UMIP-protected instructions (in the form of a SIGSEGV signal), it can be
@@ -36,8 +36,8 @@
* DOSEMU2) rely on this subset of instructions to function.
*
* The instructions protected by UMIP can be split in two groups. Those which
- * return a kernel memory address (sgdt and sidt) and those which return a
- * value (sldt, str and smsw).
+ * return a kernel memory address (SGDT and SIDT) and those which return a
+ * value (SLDT, STR and SMSW).
*
* For the instructions that return a kernel memory address, applications
* such as WineHQ rely on the result being located in the kernel memory space,
@@ -45,15 +45,14 @@
* 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).
*
- * Also, emulation is provided only for 32-bit processes; 64-bit processes
- * that attempt to use the instructions that UMIP protects will receive the
- * SIGSEGV signal issued as a consequence of the general protection fault.
+ * Emulation is provided for both 32-bit and 64-bit processes.
*
* Care is taken to appropriately emulate the results when segmentation is
* used. That is, rather than relying on USER_DS and USER_CS, the function
@@ -63,17 +62,18 @@
* application uses a local descriptor table.
*/
-#define UMIP_DUMMY_GDT_BASE 0xfffe0000
-#define UMIP_DUMMY_IDT_BASE 0xffff0000
+#define UMIP_DUMMY_GDT_BASE 0xfffffffffffe0000ULL
+#define UMIP_DUMMY_IDT_BASE 0xffffffffffff0000ULL
/*
* The SGDT and SIDT instructions store the contents of the global descriptor
* table and interrupt table registers, respectively. The destination is a
* memory operand of X+2 bytes. X bytes are used to store the base address of
- * the table and 2 bytes are used to store the limit. In 32-bit processes, the
- * only processes for which emulation is provided, X has a value of 4.
+ * the table and 2 bytes are used to store the limit. In 32-bit processes X
+ * has a value of 4, in 64-bit processes X has a value of 8.
*/
-#define UMIP_GDT_IDT_BASE_SIZE 4
+#define UMIP_GDT_IDT_BASE_SIZE_64BIT 8
+#define UMIP_GDT_IDT_BASE_SIZE_32BIT 4
#define UMIP_GDT_IDT_LIMIT_SIZE 2
#define UMIP_INST_SGDT 0 /* 0F 01 /0 */
@@ -82,7 +82,7 @@
#define UMIP_INST_SLDT 3 /* 0F 00 /0 */
#define UMIP_INST_STR 4 /* 0F 00 /1 */
-const char * const umip_insns[5] = {
+static const char * const umip_insns[5] = {
[UMIP_INST_SGDT] = "SGDT",
[UMIP_INST_SIDT] = "SIDT",
[UMIP_INST_SMSW] = "SMSW",
@@ -92,8 +92,8 @@ const char * const umip_insns[5] = {
#define umip_pr_err(regs, fmt, ...) \
umip_printk(regs, KERN_ERR, fmt, ##__VA_ARGS__)
-#define umip_pr_warning(regs, fmt, ...) \
- umip_printk(regs, KERN_WARNING, fmt, ##__VA_ARGS__)
+#define umip_pr_debug(regs, fmt, ...) \
+ umip_printk(regs, KERN_DEBUG, fmt, ##__VA_ARGS__)
/**
* umip_printk() - Print a rate-limited message
@@ -156,15 +156,26 @@ static int identify_insn(struct insn *insn)
if (!insn->modrm.nbytes)
return -EINVAL;
- /* All the instructions of interest start with 0x0f. */
- if (insn->opcode.bytes[0] != 0xf)
+ /* The instructions of interest have 2-byte opcodes: 0F 00 or 0F 01. */
+ if (insn->opcode.nbytes < 2 || insn->opcode.bytes[0] != 0xf)
return -EINVAL;
if (insn->opcode.bytes[1] == 0x1) {
switch (X86_MODRM_REG(insn->modrm.value)) {
case 0:
+ /* The reg form of 0F 01 /0 encodes VMX instructions. */
+ if (X86_MODRM_MOD(insn->modrm.value) == 3)
+ return -EINVAL;
+
return UMIP_INST_SGDT;
case 1:
+ /*
+ * The reg form of 0F 01 /1 encodes MONITOR/MWAIT,
+ * STAC/CLAC, and ENCLS.
+ */
+ if (X86_MODRM_MOD(insn->modrm.value) == 3)
+ return -EINVAL;
+
return UMIP_INST_SIDT;
case 4:
return UMIP_INST_SMSW;
@@ -189,6 +200,7 @@ static int identify_insn(struct insn *insn)
* @umip_inst: A constant indicating the instruction to emulate
* @data: Buffer into which the dummy result is stored
* @data_size: Size of the emulated result
+ * @x86_64: true if process is 64-bit, false otherwise
*
* Emulate an instruction protected by UMIP and provide a dummy result. The
* result of the emulation is saved in @data. The size of the results depends
@@ -202,11 +214,8 @@ static int identify_insn(struct insn *insn)
* 0 on success, -EINVAL on error while emulating.
*/
static int emulate_umip_insn(struct insn *insn, int umip_inst,
- unsigned char *data, int *data_size)
+ unsigned char *data, int *data_size, bool x86_64)
{
- unsigned long dummy_base_addr, dummy_value;
- unsigned short dummy_limit = 0;
-
if (!data || !data_size || !insn)
return -EINVAL;
/*
@@ -219,6 +228,9 @@ static int emulate_umip_insn(struct insn *insn, int umip_inst,
* is always returned irrespective of the operand size.
*/
if (umip_inst == UMIP_INST_SGDT || umip_inst == UMIP_INST_SIDT) {
+ u64 dummy_base_addr;
+ u16 dummy_limit = 0;
+
/* SGDT and SIDT do not use registers operands. */
if (X86_MODRM_MOD(insn->modrm.value) == 3)
return -EINVAL;
@@ -228,21 +240,50 @@ static int emulate_umip_insn(struct insn *insn, int umip_inst,
else
dummy_base_addr = UMIP_DUMMY_IDT_BASE;
- *data_size = UMIP_GDT_IDT_LIMIT_SIZE + UMIP_GDT_IDT_BASE_SIZE;
+ /*
+ * 64-bit processes use the entire dummy base address.
+ * 32-bit processes use the lower 32 bits of the base address.
+ * dummy_base_addr is always 64 bits, but we memcpy the correct
+ * number of bytes from it to the destination.
+ */
+ if (x86_64)
+ *data_size = UMIP_GDT_IDT_BASE_SIZE_64BIT;
+ else
+ *data_size = UMIP_GDT_IDT_BASE_SIZE_32BIT;
- memcpy(data + 2, &dummy_base_addr, UMIP_GDT_IDT_BASE_SIZE);
+ memcpy(data + 2, &dummy_base_addr, *data_size);
+
+ *data_size += UMIP_GDT_IDT_LIMIT_SIZE;
memcpy(data, &dummy_limit, UMIP_GDT_IDT_LIMIT_SIZE);
- } else if (umip_inst == UMIP_INST_SMSW) {
- 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.
+ * significant bytes.
*/
if (X86_MODRM_MOD(insn->modrm.value) == 3)
*data_size = insn->opnd_bytes;
@@ -250,7 +291,6 @@ 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;
}
@@ -277,7 +317,7 @@ static void force_sig_info_umip_fault(void __user *addr, struct pt_regs *regs)
tsk->thread.error_code = X86_PF_USER | X86_PF_WRITE;
tsk->thread.trap_nr = X86_TRAP_PF;
- force_sig_fault(SIGSEGV, SEGV_MAPERR, addr, tsk);
+ force_sig_fault(SIGSEGV, SEGV_MAPERR, addr);
if (!(show_unhandled_signals && unhandled_signal(tsk, SIGSEGV)))
return;
@@ -290,11 +330,10 @@ static void force_sig_info_umip_fault(void __user *addr, struct pt_regs *regs)
* fixup_umip_exception() - Fixup a general protection fault caused by UMIP
* @regs: Registers as saved when entering the #GP handler
*
- * The instructions sgdt, sidt, str, smsw, sldt cause a general protection
- * fault if executed with CPL > 0 (i.e., from user space). If the offending
- * user-space process is not in long mode, this function fixes the exception
- * up and provides dummy results for sgdt, sidt and smsw; str and sldt are not
- * fixed up. Also long mode user-space processes are not fixed up.
+ * The instructions SGDT, SIDT, STR, SMSW and SLDT cause a general protection
+ * fault if executed with CPL > 0 (i.e., from user space). This function fixes
+ * the exception up and provides dummy results for SGDT, SIDT and SMSW; STR
+ * and SLDT are not fixed up.
*
* If operands are memory addresses, results are copied to user-space memory as
* indicated by the instruction pointed by eIP using the registers indicated in
@@ -307,79 +346,39 @@ static void force_sig_info_umip_fault(void __user *addr, struct pt_regs *regs)
*/
bool fixup_umip_exception(struct pt_regs *regs)
{
- int not_copied, nr_copied, reg_offset, dummy_data_size, umip_inst;
- unsigned long seg_base = 0, *reg_addr;
+ int nr_copied, reg_offset, dummy_data_size, umip_inst;
/* 10 bytes is the maximum size of the result of UMIP instructions */
unsigned char dummy_data[10] = { 0 };
unsigned char buf[MAX_INSN_SIZE];
+ unsigned long *reg_addr;
void __user *uaddr;
struct insn insn;
- int seg_defs;
if (!regs)
return false;
/*
- * If not in user-space long mode, a custom code segment could be in
- * use. This is true in protected mode (if the process defined a local
- * descriptor table), or virtual-8086 mode. In most of the cases
- * seg_base will be zero as in USER_CS.
- */
- if (!user_64bit_mode(regs))
- seg_base = insn_get_seg_base(regs, INAT_SEG_REG_CS);
-
- if (seg_base == -1L)
- return false;
-
- not_copied = copy_from_user(buf, (void __user *)(seg_base + regs->ip),
- sizeof(buf));
- nr_copied = sizeof(buf) - not_copied;
-
- /*
- * The copy_from_user above could have failed if user code is protected
- * by a memory protection key. Give up on emulation in such a case.
- * Should we issue a page fault?
+ * Give up on emulation if fetching the instruction failed. Should a
+ * page fault or a #GP be issued?
*/
- if (!nr_copied)
+ nr_copied = insn_fetch_from_user(regs, buf);
+ if (nr_copied <= 0)
return false;
- insn_init(&insn, buf, nr_copied, user_64bit_mode(regs));
-
- /*
- * Override the default operand and address sizes with what is specified
- * in the code segment descriptor. The instruction decoder only sets
- * the address size it to either 4 or 8 address bytes and does nothing
- * for the operand bytes. This OK for most of the cases, but we could
- * have special cases where, for instance, a 16-bit code segment
- * descriptor is used.
- * If there is an address override prefix, the instruction decoder
- * correctly updates these values, even for 16-bit defaults.
- */
- seg_defs = insn_get_code_seg_params(regs);
- if (seg_defs == -EINVAL)
- return false;
-
- insn.addr_bytes = INSN_CODE_SEG_ADDR_SZ(seg_defs);
- insn.opnd_bytes = INSN_CODE_SEG_OPND_SZ(seg_defs);
-
- insn_get_length(&insn);
- if (nr_copied < insn.length)
+ if (!insn_decode_from_regs(&insn, regs, buf, nr_copied))
return false;
umip_inst = identify_insn(&insn);
if (umip_inst < 0)
return false;
- umip_pr_warning(regs, "%s instruction cannot be used by applications.\n",
+ umip_pr_debug(regs, "%s instruction cannot be used by applications.\n",
umip_insns[umip_inst]);
- /* Do not emulate SLDT, STR or user long mode processes. */
- if (umip_inst == UMIP_INST_STR || umip_inst == UMIP_INST_SLDT || user_64bit_mode(regs))
- return false;
-
- umip_pr_warning(regs, "For now, expensive software emulation returns the result.\n");
+ umip_pr_debug(regs, "For now, expensive software emulation returns the result.\n");
- if (emulate_umip_insn(&insn, umip_inst, dummy_data, &dummy_data_size))
+ if (emulate_umip_insn(&insn, umip_inst, dummy_data, &dummy_data_size,
+ user_64bit_mode(regs)))
return false;
/*
generated by cgit (git 2.34.1) at 2025-12-24 21:12:09 +0000