Commit dd649bd0 authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Thomas Gleixner

x86/cpu: Add 'unsafe_fsgsbase' to enable CR4.FSGSBASE

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: default avatarAndy Lutomirski <luto@kernel.org>
Signed-off-by: default avatarChang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Reviewed-by: default avatarAndi Kleen <ak@linux.intel.com>
Reviewed-by: default avatarAndy Lutomirski <luto@kernel.org>
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
parent fddf8ba1
...@@ -3079,6 +3079,9 @@ ...@@ -3079,6 +3079,9 @@
no5lvl [X86-64] Disable 5-level paging mode. Forces no5lvl [X86-64] Disable 5-level paging mode. Forces
kernel to use 4-level paging instead. kernel to use 4-level paging instead.
unsafe_fsgsbase [X86] Allow FSGSBASE instructions. This will be
replaced with a nofsgsbase flag.
no_console_suspend no_console_suspend
[HW] Never suspend the console [HW] Never suspend the console
Disable suspending of consoles during suspend and Disable suspending of consoles during suspend and
......
...@@ -441,6 +441,22 @@ static void __init setup_cr_pinning(void) ...@@ -441,6 +441,22 @@ static void __init setup_cr_pinning(void)
static_key_enable(&cr_pinning.key); 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. * Protection Keys are not available in 32-bit mode.
*/ */
...@@ -1495,6 +1511,14 @@ static void identify_cpu(struct cpuinfo_x86 *c) ...@@ -1495,6 +1511,14 @@ static void identify_cpu(struct cpuinfo_x86 *c)
setup_smap(c); setup_smap(c);
setup_umip(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. * The vendor-specific functions might have changed features.
* Now we do "generic changes." * Now we do "generic changes."
......
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