linux-stable/arch/x86/kernel/traps.c
Linus Torvalds cc0356d6a0 - Do not #GP on userspace use of CLI/STI but pretend it was a NOP to
keep old userspace from breaking. Adjust the corresponding iopl selftest
 to that.
 
 - Improve stack overflow warnings to say which stack got overflowed and
 raise the exception stack sizes to 2 pages since overflowing the single
 page of exception stack is very easy to do nowadays with all the tracing
 machinery enabled. With that, rip out the custom mapping of AMD SEV's
 too.
 
 - A bunch of changes in preparation for FGKASLR like supporting more
 than 64K section headers in the relocs tool, correct ORC lookup table
 size to cover the whole kernel .text and other adjustments.
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Merge tag 'x86_core_for_v5.16_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 core updates from Borislav Petkov:

 - Do not #GP on userspace use of CLI/STI but pretend it was a NOP to
   keep old userspace from breaking. Adjust the corresponding iopl
   selftest to that.

 - Improve stack overflow warnings to say which stack got overflowed and
   raise the exception stack sizes to 2 pages since overflowing the
   single page of exception stack is very easy to do nowadays with all
   the tracing machinery enabled. With that, rip out the custom mapping
   of AMD SEV's too.

 - A bunch of changes in preparation for FGKASLR like supporting more
   than 64K section headers in the relocs tool, correct ORC lookup table
   size to cover the whole kernel .text and other adjustments.

* tag 'x86_core_for_v5.16_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  selftests/x86/iopl: Adjust to the faked iopl CLI/STI usage
  vmlinux.lds.h: Have ORC lookup cover entire _etext - _stext
  x86/boot/compressed: Avoid duplicate malloc() implementations
  x86/boot: Allow a "silent" kaslr random byte fetch
  x86/tools/relocs: Support >64K section headers
  x86/sev: Make the #VC exception stacks part of the default stacks storage
  x86: Increase exception stack sizes
  x86/mm/64: Improve stack overflow warnings
  x86/iopl: Fake iopl(3) CLI/STI usage
2021-11-02 07:56:47 -07:00

1241 lines
33 KiB
C

/*
* Copyright (C) 1991, 1992 Linus Torvalds
* Copyright (C) 2000, 2001, 2002 Andi Kleen, SuSE Labs
*
* Pentium III FXSR, SSE support
* Gareth Hughes <gareth@valinux.com>, May 2000
*/
/*
* Handle hardware traps and faults.
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/context_tracking.h>
#include <linux/interrupt.h>
#include <linux/kallsyms.h>
#include <linux/spinlock.h>
#include <linux/kprobes.h>
#include <linux/uaccess.h>
#include <linux/kdebug.h>
#include <linux/kgdb.h>
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/ptrace.h>
#include <linux/uprobes.h>
#include <linux/string.h>
#include <linux/delay.h>
#include <linux/errno.h>
#include <linux/kexec.h>
#include <linux/sched.h>
#include <linux/sched/task_stack.h>
#include <linux/timer.h>
#include <linux/init.h>
#include <linux/bug.h>
#include <linux/nmi.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/io.h>
#include <linux/hardirq.h>
#include <linux/atomic.h>
#include <asm/stacktrace.h>
#include <asm/processor.h>
#include <asm/debugreg.h>
#include <asm/realmode.h>
#include <asm/text-patching.h>
#include <asm/ftrace.h>
#include <asm/traps.h>
#include <asm/desc.h>
#include <asm/fpu/api.h>
#include <asm/cpu.h>
#include <asm/cpu_entry_area.h>
#include <asm/mce.h>
#include <asm/fixmap.h>
#include <asm/mach_traps.h>
#include <asm/alternative.h>
#include <asm/fpu/xstate.h>
#include <asm/vm86.h>
#include <asm/umip.h>
#include <asm/insn.h>
#include <asm/insn-eval.h>
#include <asm/vdso.h>
#ifdef CONFIG_X86_64
#include <asm/x86_init.h>
#include <asm/proto.h>
#else
#include <asm/processor-flags.h>
#include <asm/setup.h>
#include <asm/proto.h>
#endif
DECLARE_BITMAP(system_vectors, NR_VECTORS);
static inline void cond_local_irq_enable(struct pt_regs *regs)
{
if (regs->flags & X86_EFLAGS_IF)
local_irq_enable();
}
static inline void cond_local_irq_disable(struct pt_regs *regs)
{
if (regs->flags & X86_EFLAGS_IF)
local_irq_disable();
}
__always_inline int is_valid_bugaddr(unsigned long addr)
{
if (addr < TASK_SIZE_MAX)
return 0;
/*
* We got #UD, if the text isn't readable we'd have gotten
* a different exception.
*/
return *(unsigned short *)addr == INSN_UD2;
}
static nokprobe_inline int
do_trap_no_signal(struct task_struct *tsk, int trapnr, const char *str,
struct pt_regs *regs, long error_code)
{
if (v8086_mode(regs)) {
/*
* Traps 0, 1, 3, 4, and 5 should be forwarded to vm86.
* On nmi (interrupt 2), do_trap should not be called.
*/
if (trapnr < X86_TRAP_UD) {
if (!handle_vm86_trap((struct kernel_vm86_regs *) regs,
error_code, trapnr))
return 0;
}
} else if (!user_mode(regs)) {
if (fixup_exception(regs, trapnr, error_code, 0))
return 0;
tsk->thread.error_code = error_code;
tsk->thread.trap_nr = trapnr;
die(str, regs, error_code);
} else {
if (fixup_vdso_exception(regs, trapnr, error_code, 0))
return 0;
}
/*
* We want error_code and trap_nr set for userspace faults and
* kernelspace faults which result in die(), but not
* kernelspace faults which are fixed up. die() gives the
* process no chance to handle the signal and notice the
* kernel fault information, so that won't result in polluting
* the information about previously queued, but not yet
* delivered, faults. See also exc_general_protection below.
*/
tsk->thread.error_code = error_code;
tsk->thread.trap_nr = trapnr;
return -1;
}
static void show_signal(struct task_struct *tsk, int signr,
const char *type, const char *desc,
struct pt_regs *regs, long error_code)
{
if (show_unhandled_signals && unhandled_signal(tsk, signr) &&
printk_ratelimit()) {
pr_info("%s[%d] %s%s ip:%lx sp:%lx error:%lx",
tsk->comm, task_pid_nr(tsk), type, desc,
regs->ip, regs->sp, error_code);
print_vma_addr(KERN_CONT " in ", regs->ip);
pr_cont("\n");
}
}
static void
do_trap(int trapnr, int signr, char *str, struct pt_regs *regs,
long error_code, int sicode, void __user *addr)
{
struct task_struct *tsk = current;
if (!do_trap_no_signal(tsk, trapnr, str, regs, error_code))
return;
show_signal(tsk, signr, "trap ", str, regs, error_code);
if (!sicode)
force_sig(signr);
else
force_sig_fault(signr, sicode, addr);
}
NOKPROBE_SYMBOL(do_trap);
static void do_error_trap(struct pt_regs *regs, long error_code, char *str,
unsigned long trapnr, int signr, int sicode, void __user *addr)
{
RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
if (notify_die(DIE_TRAP, str, regs, error_code, trapnr, signr) !=
NOTIFY_STOP) {
cond_local_irq_enable(regs);
do_trap(trapnr, signr, str, regs, error_code, sicode, addr);
cond_local_irq_disable(regs);
}
}
/*
* Posix requires to provide the address of the faulting instruction for
* SIGILL (#UD) and SIGFPE (#DE) in the si_addr member of siginfo_t.
*
* This address is usually regs->ip, but when an uprobe moved the code out
* of line then regs->ip points to the XOL code which would confuse
* anything which analyzes the fault address vs. the unmodified binary. If
* a trap happened in XOL code then uprobe maps regs->ip back to the
* original instruction address.
*/
static __always_inline void __user *error_get_trap_addr(struct pt_regs *regs)
{
return (void __user *)uprobe_get_trap_addr(regs);
}
DEFINE_IDTENTRY(exc_divide_error)
{
do_error_trap(regs, 0, "divide error", X86_TRAP_DE, SIGFPE,
FPE_INTDIV, error_get_trap_addr(regs));
}
DEFINE_IDTENTRY(exc_overflow)
{
do_error_trap(regs, 0, "overflow", X86_TRAP_OF, SIGSEGV, 0, NULL);
}
#ifdef CONFIG_X86_F00F_BUG
void handle_invalid_op(struct pt_regs *regs)
#else
static inline void handle_invalid_op(struct pt_regs *regs)
#endif
{
do_error_trap(regs, 0, "invalid opcode", X86_TRAP_UD, SIGILL,
ILL_ILLOPN, error_get_trap_addr(regs));
}
static noinstr bool handle_bug(struct pt_regs *regs)
{
bool handled = false;
if (!is_valid_bugaddr(regs->ip))
return handled;
/*
* All lies, just get the WARN/BUG out.
*/
instrumentation_begin();
/*
* Since we're emulating a CALL with exceptions, restore the interrupt
* state to what it was at the exception site.
*/
if (regs->flags & X86_EFLAGS_IF)
raw_local_irq_enable();
if (report_bug(regs->ip, regs) == BUG_TRAP_TYPE_WARN) {
regs->ip += LEN_UD2;
handled = true;
}
if (regs->flags & X86_EFLAGS_IF)
raw_local_irq_disable();
instrumentation_end();
return handled;
}
DEFINE_IDTENTRY_RAW(exc_invalid_op)
{
irqentry_state_t state;
/*
* We use UD2 as a short encoding for 'CALL __WARN', as such
* handle it before exception entry to avoid recursive WARN
* in case exception entry is the one triggering WARNs.
*/
if (!user_mode(regs) && handle_bug(regs))
return;
state = irqentry_enter(regs);
instrumentation_begin();
handle_invalid_op(regs);
instrumentation_end();
irqentry_exit(regs, state);
}
DEFINE_IDTENTRY(exc_coproc_segment_overrun)
{
do_error_trap(regs, 0, "coprocessor segment overrun",
X86_TRAP_OLD_MF, SIGFPE, 0, NULL);
}
DEFINE_IDTENTRY_ERRORCODE(exc_invalid_tss)
{
do_error_trap(regs, error_code, "invalid TSS", X86_TRAP_TS, SIGSEGV,
0, NULL);
}
DEFINE_IDTENTRY_ERRORCODE(exc_segment_not_present)
{
do_error_trap(regs, error_code, "segment not present", X86_TRAP_NP,
SIGBUS, 0, NULL);
}
DEFINE_IDTENTRY_ERRORCODE(exc_stack_segment)
{
do_error_trap(regs, error_code, "stack segment", X86_TRAP_SS, SIGBUS,
0, NULL);
}
DEFINE_IDTENTRY_ERRORCODE(exc_alignment_check)
{
char *str = "alignment check";
if (notify_die(DIE_TRAP, str, regs, error_code, X86_TRAP_AC, SIGBUS) == NOTIFY_STOP)
return;
if (!user_mode(regs))
die("Split lock detected\n", regs, error_code);
local_irq_enable();
if (handle_user_split_lock(regs, error_code))
goto out;
do_trap(X86_TRAP_AC, SIGBUS, "alignment check", regs,
error_code, BUS_ADRALN, NULL);
out:
local_irq_disable();
}
#ifdef CONFIG_VMAP_STACK
__visible void __noreturn handle_stack_overflow(struct pt_regs *regs,
unsigned long fault_address,
struct stack_info *info)
{
const char *name = stack_type_name(info->type);
printk(KERN_EMERG "BUG: %s stack guard page was hit at %p (stack is %p..%p)\n",
name, (void *)fault_address, info->begin, info->end);
die("stack guard page", regs, 0);
/* Be absolutely certain we don't return. */
panic("%s stack guard hit", name);
}
#endif
/*
* Runs on an IST stack for x86_64 and on a special task stack for x86_32.
*
* On x86_64, this is more or less a normal kernel entry. Notwithstanding the
* SDM's warnings about double faults being unrecoverable, returning works as
* expected. Presumably what the SDM actually means is that the CPU may get
* the register state wrong on entry, so returning could be a bad idea.
*
* Various CPU engineers have promised that double faults due to an IRET fault
* while the stack is read-only are, in fact, recoverable.
*
* On x86_32, this is entered through a task gate, and regs are synthesized
* from the TSS. Returning is, in principle, okay, but changes to regs will
* be lost. If, for some reason, we need to return to a context with modified
* regs, the shim code could be adjusted to synchronize the registers.
*
* The 32bit #DF shim provides CR2 already as an argument. On 64bit it needs
* to be read before doing anything else.
*/
DEFINE_IDTENTRY_DF(exc_double_fault)
{
static const char str[] = "double fault";
struct task_struct *tsk = current;
#ifdef CONFIG_VMAP_STACK
unsigned long address = read_cr2();
struct stack_info info;
#endif
#ifdef CONFIG_X86_ESPFIX64
extern unsigned char native_irq_return_iret[];
/*
* If IRET takes a non-IST fault on the espfix64 stack, then we
* end up promoting it to a doublefault. In that case, take
* advantage of the fact that we're not using the normal (TSS.sp0)
* stack right now. We can write a fake #GP(0) frame at TSS.sp0
* and then modify our own IRET frame so that, when we return,
* we land directly at the #GP(0) vector with the stack already
* set up according to its expectations.
*
* The net result is that our #GP handler will think that we
* entered from usermode with the bad user context.
*
* No need for nmi_enter() here because we don't use RCU.
*/
if (((long)regs->sp >> P4D_SHIFT) == ESPFIX_PGD_ENTRY &&
regs->cs == __KERNEL_CS &&
regs->ip == (unsigned long)native_irq_return_iret)
{
struct pt_regs *gpregs = (struct pt_regs *)this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1;
unsigned long *p = (unsigned long *)regs->sp;
/*
* regs->sp points to the failing IRET frame on the
* ESPFIX64 stack. Copy it to the entry stack. This fills
* in gpregs->ss through gpregs->ip.
*
*/
gpregs->ip = p[0];
gpregs->cs = p[1];
gpregs->flags = p[2];
gpregs->sp = p[3];
gpregs->ss = p[4];
gpregs->orig_ax = 0; /* Missing (lost) #GP error code */
/*
* Adjust our frame so that we return straight to the #GP
* vector with the expected RSP value. This is safe because
* we won't enable interrupts or schedule before we invoke
* general_protection, so nothing will clobber the stack
* frame we just set up.
*
* We will enter general_protection with kernel GSBASE,
* which is what the stub expects, given that the faulting
* RIP will be the IRET instruction.
*/
regs->ip = (unsigned long)asm_exc_general_protection;
regs->sp = (unsigned long)&gpregs->orig_ax;
return;
}
#endif
irqentry_nmi_enter(regs);
instrumentation_begin();
notify_die(DIE_TRAP, str, regs, error_code, X86_TRAP_DF, SIGSEGV);
tsk->thread.error_code = error_code;
tsk->thread.trap_nr = X86_TRAP_DF;
#ifdef CONFIG_VMAP_STACK
/*
* If we overflow the stack into a guard page, the CPU will fail
* to deliver #PF and will send #DF instead. Similarly, if we
* take any non-IST exception while too close to the bottom of
* the stack, the processor will get a page fault while
* delivering the exception and will generate a double fault.
*
* According to the SDM (footnote in 6.15 under "Interrupt 14 -
* Page-Fault Exception (#PF):
*
* Processors update CR2 whenever a page fault is detected. If a
* second page fault occurs while an earlier page fault is being
* delivered, the faulting linear address of the second fault will
* overwrite the contents of CR2 (replacing the previous
* address). These updates to CR2 occur even if the page fault
* results in a double fault or occurs during the delivery of a
* double fault.
*
* The logic below has a small possibility of incorrectly diagnosing
* some errors as stack overflows. For example, if the IDT or GDT
* gets corrupted such that #GP delivery fails due to a bad descriptor
* causing #GP and we hit this condition while CR2 coincidentally
* points to the stack guard page, we'll think we overflowed the
* stack. Given that we're going to panic one way or another
* if this happens, this isn't necessarily worth fixing.
*
* If necessary, we could improve the test by only diagnosing
* a stack overflow if the saved RSP points within 47 bytes of
* the bottom of the stack: if RSP == tsk_stack + 48 and we
* take an exception, the stack is already aligned and there
* will be enough room SS, RSP, RFLAGS, CS, RIP, and a
* possible error code, so a stack overflow would *not* double
* fault. With any less space left, exception delivery could
* fail, and, as a practical matter, we've overflowed the
* stack even if the actual trigger for the double fault was
* something else.
*/
if (get_stack_guard_info((void *)address, &info))
handle_stack_overflow(regs, address, &info);
#endif
pr_emerg("PANIC: double fault, error_code: 0x%lx\n", error_code);
die("double fault", regs, error_code);
panic("Machine halted.");
instrumentation_end();
}
DEFINE_IDTENTRY(exc_bounds)
{
if (notify_die(DIE_TRAP, "bounds", regs, 0,
X86_TRAP_BR, SIGSEGV) == NOTIFY_STOP)
return;
cond_local_irq_enable(regs);
if (!user_mode(regs))
die("bounds", regs, 0);
do_trap(X86_TRAP_BR, SIGSEGV, "bounds", regs, 0, 0, NULL);
cond_local_irq_disable(regs);
}
enum kernel_gp_hint {
GP_NO_HINT,
GP_NON_CANONICAL,
GP_CANONICAL
};
/*
* When an uncaught #GP occurs, try to determine the memory address accessed by
* the instruction and return that address to the caller. Also, try to figure
* out whether any part of the access to that address was non-canonical.
*/
static enum kernel_gp_hint get_kernel_gp_address(struct pt_regs *regs,
unsigned long *addr)
{
u8 insn_buf[MAX_INSN_SIZE];
struct insn insn;
int ret;
if (copy_from_kernel_nofault(insn_buf, (void *)regs->ip,
MAX_INSN_SIZE))
return GP_NO_HINT;
ret = insn_decode_kernel(&insn, insn_buf);
if (ret < 0)
return GP_NO_HINT;
*addr = (unsigned long)insn_get_addr_ref(&insn, regs);
if (*addr == -1UL)
return GP_NO_HINT;
#ifdef CONFIG_X86_64
/*
* Check that:
* - the operand is not in the kernel half
* - the last byte of the operand is not in the user canonical half
*/
if (*addr < ~__VIRTUAL_MASK &&
*addr + insn.opnd_bytes - 1 > __VIRTUAL_MASK)
return GP_NON_CANONICAL;
#endif
return GP_CANONICAL;
}
#define GPFSTR "general protection fault"
static bool fixup_iopl_exception(struct pt_regs *regs)
{
struct thread_struct *t = &current->thread;
unsigned char byte;
unsigned long ip;
if (!IS_ENABLED(CONFIG_X86_IOPL_IOPERM) || t->iopl_emul != 3)
return false;
if (insn_get_effective_ip(regs, &ip))
return false;
if (get_user(byte, (const char __user *)ip))
return false;
if (byte != 0xfa && byte != 0xfb)
return false;
if (!t->iopl_warn && printk_ratelimit()) {
pr_err("%s[%d] attempts to use CLI/STI, pretending it's a NOP, ip:%lx",
current->comm, task_pid_nr(current), ip);
print_vma_addr(KERN_CONT " in ", ip);
pr_cont("\n");
t->iopl_warn = 1;
}
regs->ip += 1;
return true;
}
DEFINE_IDTENTRY_ERRORCODE(exc_general_protection)
{
char desc[sizeof(GPFSTR) + 50 + 2*sizeof(unsigned long) + 1] = GPFSTR;
enum kernel_gp_hint hint = GP_NO_HINT;
struct task_struct *tsk;
unsigned long gp_addr;
int ret;
cond_local_irq_enable(regs);
if (static_cpu_has(X86_FEATURE_UMIP)) {
if (user_mode(regs) && fixup_umip_exception(regs))
goto exit;
}
if (v8086_mode(regs)) {
local_irq_enable();
handle_vm86_fault((struct kernel_vm86_regs *) regs, error_code);
local_irq_disable();
return;
}
tsk = current;
if (user_mode(regs)) {
if (fixup_iopl_exception(regs))
goto exit;
tsk->thread.error_code = error_code;
tsk->thread.trap_nr = X86_TRAP_GP;
if (fixup_vdso_exception(regs, X86_TRAP_GP, error_code, 0))
goto exit;
show_signal(tsk, SIGSEGV, "", desc, regs, error_code);
force_sig(SIGSEGV);
goto exit;
}
if (fixup_exception(regs, X86_TRAP_GP, error_code, 0))
goto exit;
tsk->thread.error_code = error_code;
tsk->thread.trap_nr = X86_TRAP_GP;
/*
* To be potentially processing a kprobe fault and to trust the result
* from kprobe_running(), we have to be non-preemptible.
*/
if (!preemptible() &&
kprobe_running() &&
kprobe_fault_handler(regs, X86_TRAP_GP))
goto exit;
ret = notify_die(DIE_GPF, desc, regs, error_code, X86_TRAP_GP, SIGSEGV);
if (ret == NOTIFY_STOP)
goto exit;
if (error_code)
snprintf(desc, sizeof(desc), "segment-related " GPFSTR);
else
hint = get_kernel_gp_address(regs, &gp_addr);
if (hint != GP_NO_HINT)
snprintf(desc, sizeof(desc), GPFSTR ", %s 0x%lx",
(hint == GP_NON_CANONICAL) ? "probably for non-canonical address"
: "maybe for address",
gp_addr);
/*
* KASAN is interested only in the non-canonical case, clear it
* otherwise.
*/
if (hint != GP_NON_CANONICAL)
gp_addr = 0;
die_addr(desc, regs, error_code, gp_addr);
exit:
cond_local_irq_disable(regs);
}
static bool do_int3(struct pt_regs *regs)
{
int res;
#ifdef CONFIG_KGDB_LOW_LEVEL_TRAP
if (kgdb_ll_trap(DIE_INT3, "int3", regs, 0, X86_TRAP_BP,
SIGTRAP) == NOTIFY_STOP)
return true;
#endif /* CONFIG_KGDB_LOW_LEVEL_TRAP */
#ifdef CONFIG_KPROBES
if (kprobe_int3_handler(regs))
return true;
#endif
res = notify_die(DIE_INT3, "int3", regs, 0, X86_TRAP_BP, SIGTRAP);
return res == NOTIFY_STOP;
}
static void do_int3_user(struct pt_regs *regs)
{
if (do_int3(regs))
return;
cond_local_irq_enable(regs);
do_trap(X86_TRAP_BP, SIGTRAP, "int3", regs, 0, 0, NULL);
cond_local_irq_disable(regs);
}
DEFINE_IDTENTRY_RAW(exc_int3)
{
/*
* poke_int3_handler() is completely self contained code; it does (and
* must) *NOT* call out to anything, lest it hits upon yet another
* INT3.
*/
if (poke_int3_handler(regs))
return;
/*
* irqentry_enter_from_user_mode() uses static_branch_{,un}likely()
* and therefore can trigger INT3, hence poke_int3_handler() must
* be done before. If the entry came from kernel mode, then use
* nmi_enter() because the INT3 could have been hit in any context
* including NMI.
*/
if (user_mode(regs)) {
irqentry_enter_from_user_mode(regs);
instrumentation_begin();
do_int3_user(regs);
instrumentation_end();
irqentry_exit_to_user_mode(regs);
} else {
irqentry_state_t irq_state = irqentry_nmi_enter(regs);
instrumentation_begin();
if (!do_int3(regs))
die("int3", regs, 0);
instrumentation_end();
irqentry_nmi_exit(regs, irq_state);
}
}
#ifdef CONFIG_X86_64
/*
* Help handler running on a per-cpu (IST or entry trampoline) stack
* to switch to the normal thread stack if the interrupted code was in
* user mode. The actual stack switch is done in entry_64.S
*/
asmlinkage __visible noinstr struct pt_regs *sync_regs(struct pt_regs *eregs)
{
struct pt_regs *regs = (struct pt_regs *)this_cpu_read(cpu_current_top_of_stack) - 1;
if (regs != eregs)
*regs = *eregs;
return regs;
}
#ifdef CONFIG_AMD_MEM_ENCRYPT
asmlinkage __visible noinstr struct pt_regs *vc_switch_off_ist(struct pt_regs *regs)
{
unsigned long sp, *stack;
struct stack_info info;
struct pt_regs *regs_ret;
/*
* In the SYSCALL entry path the RSP value comes from user-space - don't
* trust it and switch to the current kernel stack
*/
if (ip_within_syscall_gap(regs)) {
sp = this_cpu_read(cpu_current_top_of_stack);
goto sync;
}
/*
* From here on the RSP value is trusted. Now check whether entry
* happened from a safe stack. Not safe are the entry or unknown stacks,
* use the fall-back stack instead in this case.
*/
sp = regs->sp;
stack = (unsigned long *)sp;
if (!get_stack_info_noinstr(stack, current, &info) || info.type == STACK_TYPE_ENTRY ||
info.type > STACK_TYPE_EXCEPTION_LAST)
sp = __this_cpu_ist_top_va(VC2);
sync:
/*
* Found a safe stack - switch to it as if the entry didn't happen via
* IST stack. The code below only copies pt_regs, the real switch happens
* in assembly code.
*/
sp = ALIGN_DOWN(sp, 8) - sizeof(*regs_ret);
regs_ret = (struct pt_regs *)sp;
*regs_ret = *regs;
return regs_ret;
}
#endif
struct bad_iret_stack {
void *error_entry_ret;
struct pt_regs regs;
};
asmlinkage __visible noinstr
struct bad_iret_stack *fixup_bad_iret(struct bad_iret_stack *s)
{
/*
* This is called from entry_64.S early in handling a fault
* caused by a bad iret to user mode. To handle the fault
* correctly, we want to move our stack frame to where it would
* be had we entered directly on the entry stack (rather than
* just below the IRET frame) and we want to pretend that the
* exception came from the IRET target.
*/
struct bad_iret_stack tmp, *new_stack =
(struct bad_iret_stack *)__this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1;
/* Copy the IRET target to the temporary storage. */
__memcpy(&tmp.regs.ip, (void *)s->regs.sp, 5*8);
/* Copy the remainder of the stack from the current stack. */
__memcpy(&tmp, s, offsetof(struct bad_iret_stack, regs.ip));
/* Update the entry stack */
__memcpy(new_stack, &tmp, sizeof(tmp));
BUG_ON(!user_mode(&new_stack->regs));
return new_stack;
}
#endif
static bool is_sysenter_singlestep(struct pt_regs *regs)
{
/*
* We don't try for precision here. If we're anywhere in the region of
* code that can be single-stepped in the SYSENTER entry path, then
* assume that this is a useless single-step trap due to SYSENTER
* being invoked with TF set. (We don't know in advance exactly
* which instructions will be hit because BTF could plausibly
* be set.)
*/
#ifdef CONFIG_X86_32
return (regs->ip - (unsigned long)__begin_SYSENTER_singlestep_region) <
(unsigned long)__end_SYSENTER_singlestep_region -
(unsigned long)__begin_SYSENTER_singlestep_region;
#elif defined(CONFIG_IA32_EMULATION)
return (regs->ip - (unsigned long)entry_SYSENTER_compat) <
(unsigned long)__end_entry_SYSENTER_compat -
(unsigned long)entry_SYSENTER_compat;
#else
return false;
#endif
}
static __always_inline unsigned long debug_read_clear_dr6(void)
{
unsigned long dr6;
/*
* The Intel SDM says:
*
* Certain debug exceptions may clear bits 0-3. The remaining
* contents of the DR6 register are never cleared by the
* processor. To avoid confusion in identifying debug
* exceptions, debug handlers should clear the register before
* returning to the interrupted task.
*
* Keep it simple: clear DR6 immediately.
*/
get_debugreg(dr6, 6);
set_debugreg(DR6_RESERVED, 6);
dr6 ^= DR6_RESERVED; /* Flip to positive polarity */
return dr6;
}
/*
* Our handling of the processor debug registers is non-trivial.
* We do not clear them on entry and exit from the kernel. Therefore
* it is possible to get a watchpoint trap here from inside the kernel.
* However, the code in ./ptrace.c has ensured that the user can
* only set watchpoints on userspace addresses. Therefore the in-kernel
* watchpoint trap can only occur in code which is reading/writing
* from user space. Such code must not hold kernel locks (since it
* can equally take a page fault), therefore it is safe to call
* force_sig_info even though that claims and releases locks.
*
* Code in ./signal.c ensures that the debug control register
* is restored before we deliver any signal, and therefore that
* user code runs with the correct debug control register even though
* we clear it here.
*
* Being careful here means that we don't have to be as careful in a
* lot of more complicated places (task switching can be a bit lazy
* about restoring all the debug state, and ptrace doesn't have to
* find every occurrence of the TF bit that could be saved away even
* by user code)
*
* May run on IST stack.
*/
static bool notify_debug(struct pt_regs *regs, unsigned long *dr6)
{
/*
* Notifiers will clear bits in @dr6 to indicate the event has been
* consumed - hw_breakpoint_handler(), single_stop_cont().
*
* Notifiers will set bits in @virtual_dr6 to indicate the desire
* for signals - ptrace_triggered(), kgdb_hw_overflow_handler().
*/
if (notify_die(DIE_DEBUG, "debug", regs, (long)dr6, 0, SIGTRAP) == NOTIFY_STOP)
return true;
return false;
}
static __always_inline void exc_debug_kernel(struct pt_regs *regs,
unsigned long dr6)
{
/*
* Disable breakpoints during exception handling; recursive exceptions
* are exceedingly 'fun'.
*
* Since this function is NOKPROBE, and that also applies to
* HW_BREAKPOINT_X, we can't hit a breakpoint before this (XXX except a
* HW_BREAKPOINT_W on our stack)
*
* Entry text is excluded for HW_BP_X and cpu_entry_area, which
* includes the entry stack is excluded for everything.
*/
unsigned long dr7 = local_db_save();
irqentry_state_t irq_state = irqentry_nmi_enter(regs);
instrumentation_begin();
/*
* If something gets miswired and we end up here for a user mode
* #DB, we will malfunction.
*/
WARN_ON_ONCE(user_mode(regs));
if (test_thread_flag(TIF_BLOCKSTEP)) {
/*
* The SDM says "The processor clears the BTF flag when it
* generates a debug exception." but PTRACE_BLOCKSTEP requested
* it for userspace, but we just took a kernel #DB, so re-set
* BTF.
*/
unsigned long debugctl;
rdmsrl(MSR_IA32_DEBUGCTLMSR, debugctl);
debugctl |= DEBUGCTLMSR_BTF;
wrmsrl(MSR_IA32_DEBUGCTLMSR, debugctl);
}
/*
* Catch SYSENTER with TF set and clear DR_STEP. If this hit a
* watchpoint at the same time then that will still be handled.
*/
if ((dr6 & DR_STEP) && is_sysenter_singlestep(regs))
dr6 &= ~DR_STEP;
/*
* The kernel doesn't use INT1
*/
if (!dr6)
goto out;
if (notify_debug(regs, &dr6))
goto out;
/*
* The kernel doesn't use TF single-step outside of:
*
* - Kprobes, consumed through kprobe_debug_handler()
* - KGDB, consumed through notify_debug()
*
* So if we get here with DR_STEP set, something is wonky.
*
* A known way to trigger this is through QEMU's GDB stub,
* which leaks #DB into the guest and causes IST recursion.
*/
if (WARN_ON_ONCE(dr6 & DR_STEP))
regs->flags &= ~X86_EFLAGS_TF;
out:
instrumentation_end();
irqentry_nmi_exit(regs, irq_state);
local_db_restore(dr7);
}
static __always_inline void exc_debug_user(struct pt_regs *regs,
unsigned long dr6)
{
bool icebp;
/*
* If something gets miswired and we end up here for a kernel mode
* #DB, we will malfunction.
*/
WARN_ON_ONCE(!user_mode(regs));
/*
* NB: We can't easily clear DR7 here because
* irqentry_exit_to_usermode() can invoke ptrace, schedule, access
* user memory, etc. This means that a recursive #DB is possible. If
* this happens, that #DB will hit exc_debug_kernel() and clear DR7.
* Since we're not on the IST stack right now, everything will be
* fine.
*/
irqentry_enter_from_user_mode(regs);
instrumentation_begin();
/*
* Start the virtual/ptrace DR6 value with just the DR_STEP mask
* of the real DR6. ptrace_triggered() will set the DR_TRAPn bits.
*
* Userspace expects DR_STEP to be visible in ptrace_get_debugreg(6)
* even if it is not the result of PTRACE_SINGLESTEP.
*/
current->thread.virtual_dr6 = (dr6 & DR_STEP);
/*
* The SDM says "The processor clears the BTF flag when it
* generates a debug exception." Clear TIF_BLOCKSTEP to keep
* TIF_BLOCKSTEP in sync with the hardware BTF flag.
*/
clear_thread_flag(TIF_BLOCKSTEP);
/*
* If dr6 has no reason to give us about the origin of this trap,
* then it's very likely the result of an icebp/int01 trap.
* User wants a sigtrap for that.
*/
icebp = !dr6;
if (notify_debug(regs, &dr6))
goto out;
/* It's safe to allow irq's after DR6 has been saved */
local_irq_enable();
if (v8086_mode(regs)) {
handle_vm86_trap((struct kernel_vm86_regs *)regs, 0, X86_TRAP_DB);
goto out_irq;
}
/* #DB for bus lock can only be triggered from userspace. */
if (dr6 & DR_BUS_LOCK)
handle_bus_lock(regs);
/* Add the virtual_dr6 bits for signals. */
dr6 |= current->thread.virtual_dr6;
if (dr6 & (DR_STEP | DR_TRAP_BITS) || icebp)
send_sigtrap(regs, 0, get_si_code(dr6));
out_irq:
local_irq_disable();
out:
instrumentation_end();
irqentry_exit_to_user_mode(regs);
}
#ifdef CONFIG_X86_64
/* IST stack entry */
DEFINE_IDTENTRY_DEBUG(exc_debug)
{
exc_debug_kernel(regs, debug_read_clear_dr6());
}
/* User entry, runs on regular task stack */
DEFINE_IDTENTRY_DEBUG_USER(exc_debug)
{
exc_debug_user(regs, debug_read_clear_dr6());
}
#else
/* 32 bit does not have separate entry points. */
DEFINE_IDTENTRY_RAW(exc_debug)
{
unsigned long dr6 = debug_read_clear_dr6();
if (user_mode(regs))
exc_debug_user(regs, dr6);
else
exc_debug_kernel(regs, dr6);
}
#endif
/*
* Note that we play around with the 'TS' bit in an attempt to get
* the correct behaviour even in the presence of the asynchronous
* IRQ13 behaviour
*/
static void math_error(struct pt_regs *regs, int trapnr)
{
struct task_struct *task = current;
struct fpu *fpu = &task->thread.fpu;
int si_code;
char *str = (trapnr == X86_TRAP_MF) ? "fpu exception" :
"simd exception";
cond_local_irq_enable(regs);
if (!user_mode(regs)) {
if (fixup_exception(regs, trapnr, 0, 0))
goto exit;
task->thread.error_code = 0;
task->thread.trap_nr = trapnr;
if (notify_die(DIE_TRAP, str, regs, 0, trapnr,
SIGFPE) != NOTIFY_STOP)
die(str, regs, 0);
goto exit;
}
/*
* Synchronize the FPU register state to the memory register state
* if necessary. This allows the exception handler to inspect it.
*/
fpu_sync_fpstate(fpu);
task->thread.trap_nr = trapnr;
task->thread.error_code = 0;
si_code = fpu__exception_code(fpu, trapnr);
/* Retry when we get spurious exceptions: */
if (!si_code)
goto exit;
if (fixup_vdso_exception(regs, trapnr, 0, 0))
goto exit;
force_sig_fault(SIGFPE, si_code,
(void __user *)uprobe_get_trap_addr(regs));
exit:
cond_local_irq_disable(regs);
}
DEFINE_IDTENTRY(exc_coprocessor_error)
{
math_error(regs, X86_TRAP_MF);
}
DEFINE_IDTENTRY(exc_simd_coprocessor_error)
{
if (IS_ENABLED(CONFIG_X86_INVD_BUG)) {
/* AMD 486 bug: INVD in CPL 0 raises #XF instead of #GP */
if (!static_cpu_has(X86_FEATURE_XMM)) {
__exc_general_protection(regs, 0);
return;
}
}
math_error(regs, X86_TRAP_XF);
}
DEFINE_IDTENTRY(exc_spurious_interrupt_bug)
{
/*
* This addresses a Pentium Pro Erratum:
*
* PROBLEM: If the APIC subsystem is configured in mixed mode with
* Virtual Wire mode implemented through the local APIC, an
* interrupt vector of 0Fh (Intel reserved encoding) may be
* generated by the local APIC (Int 15). This vector may be
* generated upon receipt of a spurious interrupt (an interrupt
* which is removed before the system receives the INTA sequence)
* instead of the programmed 8259 spurious interrupt vector.
*
* IMPLICATION: The spurious interrupt vector programmed in the
* 8259 is normally handled by an operating system's spurious
* interrupt handler. However, a vector of 0Fh is unknown to some
* operating systems, which would crash if this erratum occurred.
*
* In theory this could be limited to 32bit, but the handler is not
* hurting and who knows which other CPUs suffer from this.
*/
}
static bool handle_xfd_event(struct pt_regs *regs)
{
u64 xfd_err;
int err;
if (!IS_ENABLED(CONFIG_X86_64) || !cpu_feature_enabled(X86_FEATURE_XFD))
return false;
rdmsrl(MSR_IA32_XFD_ERR, xfd_err);
if (!xfd_err)
return false;
wrmsrl(MSR_IA32_XFD_ERR, 0);
/* Die if that happens in kernel space */
if (WARN_ON(!user_mode(regs)))
return false;
local_irq_enable();
err = xfd_enable_feature(xfd_err);
switch (err) {
case -EPERM:
force_sig_fault(SIGILL, ILL_ILLOPC, error_get_trap_addr(regs));
break;
case -EFAULT:
force_sig(SIGSEGV);
break;
}
local_irq_disable();
return true;
}
DEFINE_IDTENTRY(exc_device_not_available)
{
unsigned long cr0 = read_cr0();
if (handle_xfd_event(regs))
return;
#ifdef CONFIG_MATH_EMULATION
if (!boot_cpu_has(X86_FEATURE_FPU) && (cr0 & X86_CR0_EM)) {
struct math_emu_info info = { };
cond_local_irq_enable(regs);
info.regs = regs;
math_emulate(&info);
cond_local_irq_disable(regs);
return;
}
#endif
/* This should not happen. */
if (WARN(cr0 & X86_CR0_TS, "CR0.TS was set")) {
/* Try to fix it up and carry on. */
write_cr0(cr0 & ~X86_CR0_TS);
} else {
/*
* Something terrible happened, and we're better off trying
* to kill the task than getting stuck in a never-ending
* loop of #NM faults.
*/
die("unexpected #NM exception", regs, 0);
}
}
#ifdef CONFIG_X86_32
DEFINE_IDTENTRY_SW(iret_error)
{
local_irq_enable();
if (notify_die(DIE_TRAP, "iret exception", regs, 0,
X86_TRAP_IRET, SIGILL) != NOTIFY_STOP) {
do_trap(X86_TRAP_IRET, SIGILL, "iret exception", regs, 0,
ILL_BADSTK, (void __user *)NULL);
}
local_irq_disable();
}
#endif
void __init trap_init(void)
{
/* Init cpu_entry_area before IST entries are set up */
setup_cpu_entry_areas();
/* Init GHCB memory pages when running as an SEV-ES guest */
sev_es_init_vc_handling();
/* Initialize TSS before setting up traps so ISTs work */
cpu_init_exception_handling();
/* Setup traps as cpu_init() might #GP */
idt_setup_traps();
cpu_init();
}