[PATCH v3 04/10] x86/traps: Allow custom fixups in handle_bug()

Peter Zijlstra
2025-02-19T16:36:50Z

The normal fixup in handle_bug() is simply continuing at the next
instruction. However upcomming patches make this the wrong thing, so
allow handlers (specifically handle_cfi_failure()) to over-ride
regs->ip.

The callchain is such that the fixup needs to be done before it is
determined if the exception is fatal, as such, revert any changes in
that case.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/kernel/traps.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)

--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -287,11 +287,12 @@ static inline void handle_invalid_op(str

static noinstr bool handle_bug(struct pt_regs *regs)
{
+ unsigned long addr = regs->ip;
bool handled = false;
int ud_type, ud_len;
s32 ud_imm;

- ud_type = decode_bug(regs->ip, &ud_imm, &ud_len);
+ ud_type = decode_bug(addr, &ud_imm, &ud_len);
if (ud_type == BUG_NONE)
return handled;

@@ -315,7 +316,8 @@ static noinstr bool handle_bug(struct pt
switch (ud_type) {
case BUG_EA:
if (handle_cfi_failure(regs) == BUG_TRAP_TYPE_WARN) {
- regs->ip += ud_len;
+ if (regs->ip == addr)
+ regs->ip += ud_len;
handled = true;
}
break;
@@ -323,7 +325,8 @@ static noinstr bool handle_bug(struct pt
case BUG_UD2:
if (report_bug(regs->ip, regs) == BUG_TRAP_TYPE_WARN ||
handle_cfi_failure(regs) == BUG_TRAP_TYPE_WARN) {
- regs->ip += ud_len;
+ if (regs->ip == addr)
+ regs->ip += ud_len;
handled = true;
}
break;
@@ -340,6 +343,9 @@ static noinstr bool handle_bug(struct pt
break;
}

+ if (!handled && regs->ip != addr)
+ regs->ip = addr;
+
if (regs->flags & X86_EFLAGS_IF)
raw_local_irq_disable();
instrumentation_end();