Commit-ID: 2032f1f96ee0da600633c6c627b9c0a2e0f8b8a6 Gitweb: https://git.kernel.org/tip/2032f1f96ee0da600633c6c627b9c0a2e0f8b8a6 Author: Andy Lutomirski <l...@kernel.org> AuthorDate: Wed, 8 May 2019 03:02:31 -0700 Committer: Thomas Gleixner <t...@linutronix.de> CommitDate: Sat, 22 Jun 2019 11:38:56 +0200
x86/cpu: Enable FSGSBASE on 64bit by default and add a chicken bit Now that FSGSBASE is fully supported, remove unsafe_fsgsbase, enable FSGSBASE by default, and add nofsgsbase to disable it. Signed-off-by: Andy Lutomirski <l...@kernel.org> Signed-off-by: Chang S. Bae <chang.seok....@intel.com> Signed-off-by: Thomas Gleixner <t...@linutronix.de> Reviewed-by: Andi Kleen <a...@linux.intel.com> Cc: Ravi Shankar <ravi.v.shan...@intel.com> Cc: H. Peter Anvin <h...@zytor.com> Link: https://lkml.kernel.org/r/1557309753-24073-17-git-send-email-chang.seok....@intel.com --- Documentation/admin-guide/kernel-parameters.txt | 3 +-- arch/x86/kernel/cpu/common.c | 32 +++++++++++-------------- 2 files changed, 15 insertions(+), 20 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index b0fa5273b0fc..35bc3c3574c6 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -2857,8 +2857,7 @@ 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. + nofsgsbase [X86] Disables FSGSBASE instructions. no_console_suspend [HW] Never suspend the console diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 71defe2d1b7c..1305f16b6105 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -366,21 +366,21 @@ out: cr4_clear_bits(X86_CR4_UMIP); } -/* - * 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) +static __init int x86_nofsgsbase_setup(char *arg) { - unsafe_fsgsbase = true; + /* Require an exact match without trailing characters. */ + if (strlen(arg)) + return 0; + + /* Do not emit a message if the feature is not present. */ + if (!boot_cpu_has(X86_FEATURE_FSGSBASE)) + return 1; + + setup_clear_cpu_cap(X86_FEATURE_FSGSBASE); + pr_info("FSGSBASE disabled via kernel command line\n"); return 1; } -__setup("unsafe_fsgsbase", setup_unsafe_fsgsbase); +__setup("nofsgsbase", x86_nofsgsbase_setup); /* * Protection Keys are not available in 32-bit mode. @@ -1387,12 +1387,8 @@ static void identify_cpu(struct cpuinfo_x86 *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); - } + if (cpu_has(c, X86_FEATURE_FSGSBASE)) + cr4_set_bits(X86_CR4_FSGSBASE); /* * The vendor-specific functions might have changed features.
