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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-390cd8e72fcsm185516f8f.80.2025.02.24.13.46.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 24 Feb 2025 13:46:13 -0800 (PST) Date: Mon, 24 Feb 2025 21:46:12 +0000 From: David Laight To: Peter Zijlstra Cc: x86@kernel.org, linux-kernel@vger.kernel.org, alyssa.milburn@intel.com, scott.d.constable@intel.com, joao@overdrivepizza.com, andrew.cooper3@citrix.com, jpoimboe@kernel.org, jose.marchesi@oracle.com, hjl.tools@gmail.com, ndesaulniers@google.com, samitolvanen@google.com, nathan@kernel.org, ojeda@kernel.org, kees@kernel.org, alexei.starovoitov@gmail.com, mhiramat@kernel.org, jmill@asu.edu Subject: Re: [PATCH v4 06/10] x86/traps: Decode LOCK Jcc.d8 #UD Message-ID: <20250224214612.5569d62c@pumpkin> In-Reply-To: <20250224124200.486463917@infradead.org> References: <20250224123703.843199044@infradead.org> <20250224124200.486463917@infradead.org> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Mon, 24 Feb 2025 13:37:09 +0100 Peter Zijlstra wrote: > Because overlapping code sequences are all the rage. > > Signed-off-by: Peter Zijlstra (Intel) > Reviewed-by: Kees Cook > --- > 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 David > * 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 > @@ -106,6 +107,7 @@ __always_inline int is_valid_bugaddr(uns > __always_inline int decode_bug(unsigned long addr, s32 *imm, int *len) > { > unsigned long start = addr; > + bool lock = false; > u8 v; > > if (addr < TASK_SIZE_MAX) > @@ -114,12 +116,29 @@ __always_inline int decode_bug(unsigned > v = *(u8 *)(addr++); > if (v == INSN_ASOP) > v = *(u8 *)(addr++); > - if (v == 0xea) { > + > + if (v == INSN_LOCK) { > + lock = true; > + v = *(u8 *)(addr++); > + } > + > + switch (v) { > + case 0x70 ... 0x7f: /* Jcc.d8 */ > + addr += 1; /* d8 */ > + *len = addr - start; > + WARN_ON_ONCE(!lock); > + return BUG_LOCK; > + > + case 0xea: > *len = addr - start; > return BUG_EA; > - } > - if (v != OPCODE_ESCAPE) > + > + case OPCODE_ESCAPE: > + break; > + > + default: > return BUG_NONE; > + } > > v = *(u8 *)(addr++); > if (v == SECOND_BYTE_OPCODE_UD2) { > @@ -322,6 +341,7 @@ static noinstr bool handle_bug(struct pt > fallthrough; > > case BUG_EA: > + case BUG_LOCK: > if (handle_cfi_failure(regs) == BUG_TRAP_TYPE_WARN) { > handled = true; > break; > > >