From 0698f29e949c4da7eb0b1d45abb00a299fd9878b Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Fri, 19 Mar 2021 16:24:59 +0800 Subject: [PATCH 2616/2944] x86/cpu: Add 'unsafe_fsgsbase' to enable CR4.FSGSBASE to #30648216 commit dd649bd0b3aa012740059b1ba31ecad28a408f7f upstream. 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 Signed-off-by: Sasha Levin Signed-off-by: Thomas Gleixner Reviewed-by: Andi Kleen Reviewed-by: Andy Lutomirski Link: https://lkml.kernel.org/r/1557309753-24073-4-git-send-email-chang.seok.bae@intel.com Link: https://lkml.kernel.org/r/20200528201402.1708239-3-sashal@kernel.org Signed-off-by: Ethan Zhao Signed-off-by: Zelin Deng Reviewed-by: Artie Ding --- Documentation/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 581f215..eabf299 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -2846,6 +2846,9 @@ 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 61e882e..8aeb39a 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -367,6 +367,22 @@ static __always_inline void setup_umip(struct cpuinfo_x86 *c) } /* + * 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. */ static bool pku_disabled; @@ -1429,6 +1445,14 @@ 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." -- 1.8.3.1