iv/linux
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

x86/entry: Treat BUG/WARN as NMI-like entries

Browse Source 
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
This commit is contained in:
Andy Lutomirski 2020-06-11 20:26:38 -07:00 committed by Thomas Gleixner
parent f0178fc01f
commit 15a416e8aa
3 changed files with 52 additions and 29 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
arch/x86/include/asm/idtentry.h
View File

@ -543,7 +543,6 @@ SYM_CODE_END(spurious_entries_start)
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_GP, exc_general_protection);
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);

64
arch/x86/kernel/traps.c
View File

@ -97,24 +97,6 @@ int is_valid_bugaddr(unsigned long addr)
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 @@ static void do_error_trap(struct pt_regs *regs, long error_code, char *str,
{
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 @@ static inline void handle_invalid_op(struct pt_regs *regs)
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)

15
arch/x86/mm/extable.c
View File

@ -204,8 +204,19 @@ void __init early_fixup_exception(struct pt_regs *regs, int trapnr)
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",