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Wed, 9 Jul 2025 02:40:37 +0000 Message-ID: Date: Tue, 8 Jul 2025 19:40:35 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCHv9 11/16] x86/traps: Communicate a LASS violation in #GP message Content-Language: en-US To: "Kirill A. Shutemov" , Andy Lutomirski , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , , "H. Peter Anvin" , Peter Zijlstra , Ard Biesheuvel , "Paul E. McKenney" , Josh Poimboeuf , Xiongwei Song , Xin Li , "Mike Rapoport (IBM)" , Brijesh Singh , Michael Roth , Tony Luck , Alexey Kardashevskiy , Alexander Shishkin CC: Jonathan Corbet , Ingo Molnar , "Pawan Gupta" , Daniel Sneddon , Kai Huang , "Sandipan Das" , Breno Leitao , Rick Edgecombe , Alexei Starovoitov , Hou Tao , Juergen Gross , Vegard Nossum , Kees Cook , Eric Biggers , Jason Gunthorpe , "Masami Hiramatsu (Google)" , Andrew Morton , Luis Chamberlain , Yuntao Wang , "Rasmus Villemoes" , Christophe Leroy , Tejun Heo , Changbin Du , Huang Shijie , "Geert Uytterhoeven" , Namhyung Kim , Arnaldo Carvalho de Melo , , , , References: <20250707080317.3791624-1-kirill.shutemov@linux.intel.com> <20250707080317.3791624-12-kirill.shutemov@linux.intel.com> From: Sohil Mehta In-Reply-To: <20250707080317.3791624-12-kirill.shutemov@linux.intel.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BYAPR08CA0048.namprd08.prod.outlook.com (2603:10b6:a03:117::25) To BYAPR11MB3320.namprd11.prod.outlook.com (2603:10b6:a03:18::25) Precedence: bulk X-Mailing-List: linux-efi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BYAPR11MB3320:EE_|SN7PR11MB7708:EE_ X-MS-Office365-Filtering-Correlation-Id: ef749e73-af4a-4907-d77a-08ddbe91fcaf X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|376014|7416014|1800799024|7053199007|921020; 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Shutemov wrote: > From: Alexander Shishkin > > Provide a more helpful message on #GP when a kernel side LASS violation > is detected. > > A NULL pointer dereference is reported if a LASS violation occurs due to > accessing the first page frame. > > Signed-off-by: Alexander Shishkin > Signed-off-by: Kirill A. Shutemov > --- > arch/x86/kernel/traps.c | 41 +++++++++++++++++++++++++++++------------ > 1 file changed, 29 insertions(+), 12 deletions(-) > Reviewed-by: Sohil Mehta A nit below. > diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c > index 59bfbdf0a1a0..4a4194e1d119 100644 > --- a/arch/x86/kernel/traps.c > +++ b/arch/x86/kernel/traps.c > @@ -636,7 +636,16 @@ DEFINE_IDTENTRY(exc_bounds) > enum kernel_gp_hint { > GP_NO_HINT, > GP_NON_CANONICAL, > - GP_CANONICAL > + GP_CANONICAL, > + GP_LASS_VIOLATION, > + GP_NULL_POINTER, > +}; > + > +static const char * const kernel_gp_hint_help[] = { > + [GP_NON_CANONICAL] = "probably for non-canonical address", > + [GP_CANONICAL] = "maybe for address", > + [GP_LASS_VIOLATION] = "LASS prevented access to address", > + [GP_NULL_POINTER] = "kernel NULL pointer dereference", > }; > > /* > @@ -664,14 +673,23 @@ static enum kernel_gp_hint get_kernel_gp_address(struct pt_regs *regs, > return GP_NO_HINT; > > #ifdef CONFIG_X86_64 Might as well get rid of the #ifdef in C code, if possible. if (!IS_ENABLED(CONFIG_X86_64) return GP_CANONICAL; or combine it with the next check. > - /* > - * Check that: > - * - the operand is not in the kernel half > - * - the last byte of the operand is not in the user canonical half > - */ > - if (*addr < ~__VIRTUAL_MASK && > - *addr + insn.opnd_bytes - 1 > __VIRTUAL_MASK) > + /* Operand is in the kernel half */ > + if (*addr >= ~__VIRTUAL_MASK) > + return GP_CANONICAL; > + > + /* The last byte of the operand is not in the user canonical half */ > + if (*addr + insn.opnd_bytes - 1 > __VIRTUAL_MASK) > return GP_NON_CANONICAL; > + > + /* > + * If LASS is enabled, NULL pointer dereference generates > + * #GP instead of #PF. > + */ > + if (*addr < PAGE_SIZE) > + return GP_NULL_POINTER; > + > + if (cpu_feature_enabled(X86_FEATURE_LASS)) > + return GP_LASS_VIOLATION; > #endif > > return GP_CANONICAL;