linux-kernel - Re: [PATCH v4 06/10] x86/traps: Decode LOCK Jcc.d8 #UD

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Message-ID: <202502251033.B8216DDA3@keescook>
Date: Tue, 25 Feb 2025 10:33:41 -0800
From: Kees Cook <kees@...nel.org>
To: David Laight <david.laight.linux@...il.com>
Cc: Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org, alyssa.milburn@...el.com,
	scott.d.constable@...el.com, joao@...rdrivepizza.com,
	andrew.cooper3@...rix.com, jpoimboe@...nel.org,
	jose.marchesi@...cle.com, hjl.tools@...il.com,
	ndesaulniers@...gle.com, samitolvanen@...gle.com, nathan@...nel.org,
	ojeda@...nel.org, alexei.starovoitov@...il.com, mhiramat@...nel.org,
	jmill@....edu
Subject: Re: [PATCH v4 06/10] x86/traps: Decode LOCK Jcc.d8 #UD

On Mon, Feb 24, 2025 at 09:46:12PM +0000, David Laight wrote:
> On Mon, 24 Feb 2025 13:37:09 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > Because overlapping code sequences are all the rage.
> > 
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> > Reviewed-by: Kees Cook <kees@...nel.org>
> > ---
> >  arch/x86/include/asm/bug.h |    2 ++
> >  arch/x86/kernel/traps.c    |   26 +++++++++++++++++++++++---
> >  2 files changed, 25 insertions(+), 3 deletions(-)
> > 
> > --- a/arch/x86/include/asm/bug.h
> > +++ b/arch/x86/include/asm/bug.h
> > @@ -17,6 +17,7 @@
> >   * In clang we have UD1s reporting UBSAN failures on X86, 64 and 32bit.
> >   */
> >  #define INSN_ASOP		0x67
> > +#define INSN_LOCK		0xf0
> >  #define OPCODE_ESCAPE		0x0f
> >  #define SECOND_BYTE_OPCODE_UD1	0xb9
> >  #define SECOND_BYTE_OPCODE_UD2	0x0b
> > @@ -26,6 +27,7 @@
> >  #define BUG_UD1			0xfffd
> >  #define BUG_UD1_UBSAN		0xfffc
> >  #define BUG_EA			0xffea
> > +#define BUG_LOCK		0xfff0
> >  
> >  #ifdef CONFIG_GENERIC_BUG
> >  
> > --- a/arch/x86/kernel/traps.c
> > +++ b/arch/x86/kernel/traps.c
> > @@ -97,6 +97,7 @@ __always_inline int is_valid_bugaddr(uns
> >   * If it's a UD1, further decode to determine its use:
> >   *
> >   * FineIBT:      ea                      (bad)
> > + * FineIBT:      0f 75 f9                lock jne . - 6
>                     ^^ nibble swapped

Oh, good catch!

-- 
Kees Cook