From: Andy Lutomirski <[email protected]> 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 <[email protected]> [chang: Fix the deactivated flag] Signed-off-by: Chang S. Bae <[email protected]> Reviewed-by: Andi Kleen <[email protected]> Cc: H. Peter Anvin <[email protected]> --- Documentation/admin-guide/kernel-parameters.txt | 3 +++ arch/x86/kernel/cpu/common.c | 25 +++++++++++++++++++++++++ 2 files changed, 28 insertions(+) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 1d1d53f..87c2260 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -2567,6 +2567,9 @@ emulation library even if a 387 maths coprocessor is present. + 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 348cf48..019bdc3 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -356,6 +356,23 @@ 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. Setting + * unsafe_fsgsbase will allow the series to be bisected if necessary. + * + * Once all the pieces are in place, this 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; @@ -1238,6 +1255,14 @@ 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." -- 2.7.4
