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Peter Anvin" , Sasha Levin Subject: [PATCH v13 02/16] x86/cpu: Add 'unsafe_fsgsbase' to enable CR4.FSGSBASE Date: Thu, 28 May 2020 16:13:48 -0400 Message-Id: <20200528201402.1708239-3-sashal@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20200528201402.1708239-1-sashal@kernel.org> References: <20200528201402.1708239-1-sashal@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Andy Lutomirski This is temporary. It will allow the next few patches to be tested incrementally. Setting unsafe_fsgsbase is a root hole. Don't do it. Signed-off-by: Andy Lutomirski Signed-off-by: Chang S. Bae Signed-off-by: Thomas Gleixner Reviewed-by: Andi Kleen Reviewed-by: Andy Lutomirski Cc: Ravi Shankar Cc: Andrew Morton Cc: Randy Dunlap Cc: H. Peter Anvin Link: https://lkml.kernel.org/r/1557309753-24073-4-git-send-email-chang.seok.bae@intel.com Signed-off-by: Sasha Levin --- .../admin-guide/kernel-parameters.txt | 3 +++ arch/x86/kernel/cpu/common.c | 24 +++++++++++++++++++ 2 files changed, 27 insertions(+) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 7bc83f3d9bdf..af3aaade195b 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -3033,6 +3033,9 @@ no5lvl [X86-64] Disable 5-level paging mode. Forces kernel to use 4-level paging instead. + unsafe_fsgsbase [X86] Allow FSGSBASE instructions. This will be + replaced with a nofsgsbase flag. + no_console_suspend [HW] Never suspend the console Disable suspending of consoles during suspend and diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index bed0cb83fe24..4224760c74e2 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -418,6 +418,22 @@ static void __init setup_cr_pinning(void) static_key_enable(&cr_pinning.key); } +/* + * Temporary hack: FSGSBASE is unsafe until a few kernel code paths are + * updated. This allows us to get the kernel ready incrementally. + * + * Once all the pieces are in place, these will go away and be replaced with + * a nofsgsbase chicken flag. + */ +static bool unsafe_fsgsbase; + +static __init int setup_unsafe_fsgsbase(char *arg) +{ + unsafe_fsgsbase = true; + return 1; +} +__setup("unsafe_fsgsbase", setup_unsafe_fsgsbase); + /* * Protection Keys are not available in 32-bit mode. */ @@ -1478,6 +1494,14 @@ static void identify_cpu(struct cpuinfo_x86 *c) setup_smap(c); setup_umip(c); + /* Enable FSGSBASE instructions if available. */ + if (cpu_has(c, X86_FEATURE_FSGSBASE)) { + if (unsafe_fsgsbase) + cr4_set_bits(X86_CR4_FSGSBASE); + else + clear_cpu_cap(c, X86_FEATURE_FSGSBASE); + } + /* * The vendor-specific functions might have changed features. * Now we do "generic changes." -- 2.25.1