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([10.237.72.28]) by orviesa002.jf.intel.com with ESMTP; 28 Oct 2024 09:11:23 -0700 From: Alexander Shishkin 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 , "Kirill A. Shutemov" , Alexey Kardashevskiy Cc: Jonathan Corbet , Alexander Shishkin , 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 Subject: [PATCH v5 10/16] x86/vsyscall: Disable LASS if vsyscall mode is set to EMULATE Date: Mon, 28 Oct 2024 18:07:58 +0200 Message-ID: <20241028160917.1380714-11-alexander.shishkin@linux.intel.com> X-Mailer: git-send-email 2.45.2 In-Reply-To: <20241028160917.1380714-1-alexander.shishkin@linux.intel.com> References: <20241028160917.1380714-1-alexander.shishkin@linux.intel.com> Precedence: bulk X-Mailing-List: linux-efi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 From: Sohil Mehta The EMULATE mode of vsyscall maps the vsyscall page into user address space which can be read directly by the user application. This mode has been deprecated recently and can only be enabled from a special command line parameter vsyscall=emulate. See commit bf00745e7791 ("x86/vsyscall: Remove CONFIG_LEGACY_VSYSCALL_EMULATE") Fixing the LASS violations during the EMULATE mode would need complex instruction decoding since the resulting #GP fault does not include any useful error information and the vsyscall address is not readily available in the RIP. At this point, no one is expected to be using the insecure and deprecated EMULATE mode. The rare usages that need support probably don't care much about security anyway. Disable LASS when EMULATE mode is requested during command line parsing to avoid breaking user software. LASS will be supported if vsyscall mode is set to XONLY or NONE. Signed-off-by: Sohil Mehta Signed-off-by: Alexander Shishkin --- arch/x86/entry/vsyscall/vsyscall_64.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c index 97608883b4b4..7c845c1db3b4 100644 --- a/arch/x86/entry/vsyscall/vsyscall_64.c +++ b/arch/x86/entry/vsyscall/vsyscall_64.c @@ -36,6 +36,7 @@ #include #include #include +#include #include #include @@ -63,6 +64,13 @@ static int __init vsyscall_setup(char *str) else return -EINVAL; + if (cpu_feature_enabled(X86_FEATURE_LASS) && + vsyscall_mode == EMULATE) { + cr4_clear_bits(X86_CR4_LASS); + setup_clear_cpu_cap(X86_FEATURE_LASS); + pr_warn_once("x86/cpu: Disabling LASS support due to vsyscall=emulate\n"); + } + return 0; }