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Shutemov" To: Andy Lutomirski , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "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 , Sohil Mehta , 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 , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-efi@vger.kernel.org, linux-mm@kvack.org, "Kirill A. Shutemov" Subject: [PATCHv9 11/16] x86/traps: Communicate a LASS violation in #GP message Date: Mon, 7 Jul 2025 11:03:11 +0300 Message-ID: <20250707080317.3791624-12-kirill.shutemov@linux.intel.com> X-Mailer: git-send-email 2.47.2 In-Reply-To: <20250707080317.3791624-1-kirill.shutemov@linux.intel.com> References: <20250707080317.3791624-1-kirill.shutemov@linux.intel.com> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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(-) 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 - /* - * 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; @@ -833,11 +851,10 @@ DEFINE_IDTENTRY_ERRORCODE(exc_general_protection) else hint = get_kernel_gp_address(regs, &gp_addr); - if (hint != GP_NO_HINT) + if (hint != GP_NO_HINT) { snprintf(desc, sizeof(desc), GPFSTR ", %s 0x%lx", - (hint == GP_NON_CANONICAL) ? "probably for non-canonical address" - : "maybe for address", - gp_addr); + kernel_gp_hint_help[hint], gp_addr); + } /* * KASAN is interested only in the non-canonical case, clear it -- 2.47.2