x86/entry: Treat BUG/WARN as NMI-like entries
BUG/WARN are cleverly optimized using UD2 to handle the BUG/WARN out of
line in an exception fixup.
But if BUG or WARN is issued in a funny RCU context, then the
idtentry_enter...() path might helpfully WARN that the RCU context is
invalid, which results in infinite recursion.
Split the BUG/WARN handling into an nmi_enter()/nmi_exit() path in
exc_invalid_op() to increase the chance to survive the experience.
[ tglx: Make the declaration match the implementation ]
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/f8fe40e0088749734b4435b554f73eee53dcf7a8.1591932307.git.luto@kernel.org
diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
index d203c54..2fc6b0c 100644
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -543,7 +543,6 @@
DECLARE_IDTENTRY(X86_TRAP_DE, exc_divide_error);
DECLARE_IDTENTRY(X86_TRAP_OF, exc_overflow);
DECLARE_IDTENTRY(X86_TRAP_BR, exc_bounds);
-DECLARE_IDTENTRY(X86_TRAP_UD, exc_invalid_op);
DECLARE_IDTENTRY(X86_TRAP_NM, exc_device_not_available);
DECLARE_IDTENTRY(X86_TRAP_OLD_MF, exc_coproc_segment_overrun);
DECLARE_IDTENTRY(X86_TRAP_SPURIOUS, exc_spurious_interrupt_bug);
@@ -561,6 +560,7 @@
DECLARE_IDTENTRY_ERRORCODE(X86_TRAP_AC, exc_alignment_check);
/* Raw exception entries which need extra work */
+DECLARE_IDTENTRY_RAW(X86_TRAP_UD, exc_invalid_op);
DECLARE_IDTENTRY_RAW(X86_TRAP_BP, exc_int3);
DECLARE_IDTENTRY_RAW_ERRORCODE(X86_TRAP_PF, exc_page_fault);
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 7febae3..af75109 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -97,24 +97,6 @@
return ud == INSN_UD0 || ud == INSN_UD2;
}
-int fixup_bug(struct pt_regs *regs, int trapnr)
-{
- if (trapnr != X86_TRAP_UD)
- return 0;
-
- switch (report_bug(regs->ip, regs)) {
- case BUG_TRAP_TYPE_NONE:
- case BUG_TRAP_TYPE_BUG:
- break;
-
- case BUG_TRAP_TYPE_WARN:
- regs->ip += LEN_UD2;
- return 1;
- }
-
- return 0;
-}
-
static nokprobe_inline int
do_trap_no_signal(struct task_struct *tsk, int trapnr, const char *str,
struct pt_regs *regs, long error_code)
@@ -190,13 +172,6 @@
{
RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
- /*
- * WARN*()s end up here; fix them up before we call the
- * notifier chain.
- */
- if (!user_mode(regs) && fixup_bug(regs, trapnr))
- return;
-
if (notify_die(DIE_TRAP, str, regs, error_code, trapnr, signr) !=
NOTIFY_STOP) {
cond_local_irq_enable(regs);
@@ -241,9 +216,46 @@
ILL_ILLOPN, error_get_trap_addr(regs));
}
-DEFINE_IDTENTRY(exc_invalid_op)
+DEFINE_IDTENTRY_RAW(exc_invalid_op)
{
+ bool rcu_exit;
+
+ /*
+ * Handle BUG/WARN like NMIs instead of like normal idtentries:
+ * if we bugged/warned in a bad RCU context, for example, the last
+ * thing we want is to BUG/WARN again in the idtentry code, ad
+ * infinitum.
+ */
+ if (!user_mode(regs) && is_valid_bugaddr(regs->ip)) {
+ enum bug_trap_type type;
+
+ nmi_enter();
+ instrumentation_begin();
+ trace_hardirqs_off_finish();
+ type = report_bug(regs->ip, regs);
+ if (regs->flags & X86_EFLAGS_IF)
+ trace_hardirqs_on_prepare();
+ instrumentation_end();
+ nmi_exit();
+
+ if (type == BUG_TRAP_TYPE_WARN) {
+ /* Skip the ud2. */
+ regs->ip += LEN_UD2;
+ return;
+ }
+
+ /*
+ * Else, if this was a BUG and report_bug returns or if this
+ * was just a normal #UD, we want to continue onward and
+ * crash.
+ */
+ }
+
+ rcu_exit = idtentry_enter_cond_rcu(regs);
+ instrumentation_begin();
handle_invalid_op(regs);
+ instrumentation_end();
+ idtentry_exit_cond_rcu(regs, rcu_exit);
}
DEFINE_IDTENTRY(exc_coproc_segment_overrun)
diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index b991aa4..1d6cb07 100644
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -204,8 +204,19 @@
if (fixup_exception(regs, trapnr, regs->orig_ax, 0))
return;
- if (fixup_bug(regs, trapnr))
- return;
+ if (trapnr == X86_TRAP_UD) {
+ if (report_bug(regs->ip, regs) == BUG_TRAP_TYPE_WARN) {
+ /* Skip the ud2. */
+ regs->ip += LEN_UD2;
+ return;
+ }
+
+ /*
+ * If this was a BUG and report_bug returns or if this
+ * was just a normal #UD, we want to continue onward and
+ * crash.
+ */
+ }
fail:
early_printk("PANIC: early exception 0x%02x IP %lx:%lx error %lx cr2 0x%lx\n",
