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x86/traps: Decode 0xEA instructions as #UD

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FineIBT will start using 0xEA as #UD. Normally '0xEA' is a 'bad',
invalid instruction for the CPU.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Kees Cook <kees@kernel.org>
Link: https://lore.kernel.org/r/20250224124200.166774696@infradead.org
This commit is contained in:
Peter Zijlstra 2025-02-24 13:37:06 +01:00 committed by Ingo Molnar
parent 5d703825fd
commit 2e044911be
2 changed files with 18 additions and 3 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

1
arch/x86/include/asm/bug.h
View file

@ -25,6 +25,7 @@
#define BUG_UD2 0xfffe
#define BUG_UD1 0xfffd
#define BUG_UD1_UBSAN 0xfffc
#define BUG_EA 0xffea
#ifdef CONFIG_GENERIC_BUG

20
arch/x86/kernel/traps.c
View file

@ -96,6 +96,7 @@ __always_inline int is_valid_bugaddr(unsigned long addr)
* Check for UD1 or UD2, accounting for Address Size Override Prefixes.
* If it's a UD1, further decode to determine its use:
*
* FineIBT: ea (bad)
* UBSan{0}: 67 0f b9 00 ud1 (%eax),%eax
* UBSan{10}: 67 0f b9 40 10 ud1 0x10(%eax),%eax
* static_call: 0f b9 cc ud1 %esp,%ecx
@ -113,6 +114,10 @@ __always_inline int decode_bug(unsigned long addr, s32 *imm, int *len)
v = *(u8 *)(addr++);
if (v == INSN_ASOP)
v = *(u8 *)(addr++);
if (v == 0xea) {
*len = addr - start;
return BUG_EA;
}
if (v != OPCODE_ESCAPE)
return BUG_NONE;
@ -309,10 +314,16 @@ static noinstr bool handle_bug(struct pt_regs *regs)
switch (ud_type) {
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 (report_bug(regs->ip, regs) == BUG_TRAP_TYPE_WARN) {
handled = true;
break;
}
fallthrough;
case BUG_EA:
if (handle_cfi_failure(regs) == BUG_TRAP_TYPE_WARN) {
handled = true;
break;
}
break;
@ -328,6 +339,9 @@ static noinstr bool handle_bug(struct pt_regs *regs)
break;
}
if (handled)
regs->ip += ud_len;
if (regs->flags & X86_EFLAGS_IF)
raw_local_irq_disable();
instrumentation_end();